Download Physice class notes

Light .................................................................................................................................................................. 1
Exp. To find the focal length of concave mirror.
1
Exp. To verify Snell’s law.
1
Exp. To measure the refractive index of water.
2
Exp. To measure the focal length of a converging lens.
2
Mechanics ......................................................................................................................................................... 3
Exp. To measure constant velocity
3
Exp. To measure constant acceleration
3
Exp. To verify conservation of momentum.
3
Exp. To verify a  F/m
4
Exp. To measure the acceleration due to gravity.
4
Exp. To verify the principle of moments
5
To verify Boyle’s Law
5
Exp. To measure g using a simple pendulum
6
Wave Motions ................................................................................................................................................... 6
Exp. To the measure the wavelength of monochromatic light.
7
Exp. To investigate the variation of the fundamental frequency of a stretched string with length.
8
Exp. To measure the speed of sound in air.
8
Heat and Temperature ....................................................................................................................................... 8
Exp. To calibrate a thermocouple thermometer.
9
Exp. To find the specific heat capacity of water
9
Exp. To measure the specific latent heat of vaporisation of water
9
Exp. To measure the specific latent heat of fusion of ice.
10
Electricity current and static .............................................................................................................................. 10
Exp. Investigate the factors affecting a parallel plate capacitor
11
Exp. To prove Ohm's law
12
Exp. To find the variation of resistance of a copper wire (metallic conductor) with temperature.
12
Exp. To find the variation of resistance of a thermistor (semi-conductor) with temperature
12
Exp. To measure the resistivity of a wire.
12
Exp. To verify joule's law
13
Exp.To investigate the variation of current with p.d (V) for a filament bulb
14
Exp.To investigate the variation of current with p.d (V) for a copper sulphate solution with copper electrodes
14
Exp. To investigate the variation of current against voltage for semi-conductor (diode).
15
Electromagnetism .............................................................................................................................................. 15
Atomic Physics.................................................................................................................................................. 16
Exp. To investigate the range of the 3 types of radiation in air.
18
Option 1 Particle Physics .................................................................................................................................. 19
Option II Applied Electricity............................................................................................................................. 21
Exp. To establish truth tables for AND and OR gates.
22
Exp. To Establish a truth table for a NOT gate
23
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Athdhéanamh Fisice
D.M.A ©
Light
Light is a form of energy, which travels at 3x108 ms-1. Light can be changed into other forms of energy e.g. a
solar cell changes light into electricity. Other forms of energy can be changed into light e.g. electricity into light
in a light bulb. Light travels in straight lines ( how can you show this?) and this
is the reason we get shadows.
O
Mirror at 45 angle
Light ray = path taken by light as is travels between two points. Luminous = a
body which emits its own light. Non-luminous = body which can only be seen
when it reflects light. Diffuse reflection = light reflected in all directions.
Regular reflection = light reflected in certain directions only.
Laws of reflection: The incident ray, reflected ray and normal all lie on the
same plane. The angle of incidence = the angle of reflection.
Real image: can be formed on a screen , inverted, light rays intersect.
Virtual image: cannot be formed on a screen, erect, light rays only appear to
Periscope
intersect.
Lateral inversion: right of object appears as left of image and vice versa.
Periscope: arrangement of two mirrors in a long tube parallel to each other at an
angle of 45o to the tube. Used for looking over the top of obstacles and in
submarines
Concave Mirrors: a) rays parallel to the principal focus are reflected through F,
b) rays through F are reflected parallel to the principal axis and c) rays through
C are reflected back along C. Where they intersect the image is formed. Concave mirrors are used for
searchlights, shaving mirrors, dentists to examine the mouth because an object inside the focus is magnified and
the right way up.
Radius of curvature = twice the focal length.
Mirror and lens formulae
1
f
=
1
u
+
1
v
m =
v
u
or
hI
ho
Real is positive convention used.
Convex Mirrors: Use the same rays as for concave mirrors. to locate the image. The image is always virtual,
erect and diminished (disadvantage of convex mirrors, why?) and f is negative and the image distance is negative.
Convex mirrors are used for car rear view and door mirrors, in shops, concealed entrances because they give a
large field of view and the image is the right way up.
Exp. To find the focal length of concave mirror.
Rem: concave mirror, object, metre
Object distance u
stick, screen and projector (light source)
Light
Concave
Place the object in front of the mirror as
source
mirror
a object, move the screen until a sharp
Object
image of the object is obtained. Measure
the object distance (u) and image
Image distance v
Screen
distance(v) distances and use the
formula to find the focal length (f).
Repeat for different object distances.
Laws of refraction: The refracted ray, normal and incident ray all lie on the same plane. The Sine of the angle of
incidence proportional to the sine of the angle of refraction (Snell's law).
Light going into a denser medium is bent towards the normal and vice versa.
Exp. To verify Snell’s law.
Rem: glass block, ray box, paper, protractor. Draw an outline of the block on the paper. Draw the normal . Use
the ray box for an incident ray and mark the ray on the paper, mark the emergent ray, remove the block and join
the rays as in A in the diagram. Measure the angles i and r. repeat for different values of i. Draw a graph of sin i
against sine r.
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i
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N
A
Refractive index
n= sin i
sin r
sin i
r
n = slope of the graph
Sin r
Refractive index (n) = real depth/ apparent depth.
Refractive index in terms of speed. The refractive index it can be proved is
the speed in the first medium divided by the speed in the second medium.
Refractive index
c
n = 1
12 c
2
c= speed of the
wave
Exp. To measure the refractive index of water.
Rem: beaker of water, plane mirror, pin as object and pin in the water. Adjust
the height of the pin until the image in the mirror has no parallax with the
image of the pin in the water. The distance between the cork pin to the mirror
= the apparent depth and the depth of the water = the real depth
. Total internal reflection: all the light is reflected and none is refracted, depends
Pin in cork
of the critical angle c for a substance. The critical angle is the angle of incidence
corresponding to an angle of refraction of 90 o. Total internal reflection occurs
mirror
when the angle of i > c. Sin c = 1/n. Total Internal Reflection is made use of in
bicycle reflectors, optical fibres for transmission of telephone calls and explains
mirages. The critical angle between two media say light and water explains what
Water
divers call Snell’s Window.
Prisms: cause light rays to be deviated on passing through them. They can be
arranged so that total internal reflection occurs through 90 o or 180o. Prisms are
used in binoculars and periscopes. They give better quality images and do not
deteriorate with age. Optical fibres: thin glass tubes which light is sent down, based on total internal reflection.
Used for telephone conversations and examining inside patients. Mirage: due to layers of hot to cold air, causing
refraction and eventually total internal reflection to give a virtual image of a patch of the sky.
Converging lens and diverging lens: use light rays a) and b) for mirrors to locate image position. The same
formulas apply as for mirrors. For a diverging lens the image is always virtual, erect and diminished so f and v
are negative.
Exp. To measure the focal length of a converging lens.
Rem: lens, metre stick, light source, object, screen. Adjust the position of the object until a sharp image is formed
on the screen. Measure v and u. repeat for different object distances. Use the formula to calculate f.
screen
v
light
u
object
source
lens
Power of a lens: The shorter the focal length the greater the converging or diverging power of a lens this is
called the power of a lens. The power of a lens is
1
1
=
measured in m-1. If two lens are in contact then the power
Power of lens (P) =
f
Focal length (f) of the combination is P = P1 + P2 and therefore if f is the
focal length of the combination then :
Human eye: Be able to draw and label. Iris: controls
the amount of light entering the eye. Retina: light
sensitive part. Cornea: transparent part in front of the
eye. Lens: focuses the incoming light. Ciliary
muscles: change the shape of the lens to focus the
light.
Defects of vision: a) long sight  cannot focus near
objects, image forms behind the retina, solve using
converging lens. b) short sight  cannot focus far
objects, image forms in front of the retina, solve using
diverging lens.
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1
f
+
1
Sclerotic (white of eye)
Aqueous
Retina
humour
Iris
(Colour of eye)
Cornea
Lens
Optic
nerve
Ciliary
muscle
Vitreous humour
1
f
2
Athdhéanamh Fisice
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Prism Binoculars: really a pair of telescopes side by side, with to 90 o prisms, one to erect the image and one to
turn it the right way round.
Spectrometer: used to examine light emitted from different substances. Consists of a table with angle scale,
telescope and collimator
Mechanics
Scalar quantities: no direction associated with them, e.g. mass.
Vector quantities: have a direction, e.g. velocity.
Displacement is distance in a given direction. (m)
Velocity = displacement/time (ms-1)
Acceleration = change in velocity/ time (ms-2)
Equations of motion: v=u+at, v2=u2+2as and s=u+½at2
Exp. To measure constant velocity
Rem. Linear air track, trolley, light gate, card, timer. Friction is overcome because the trolley rides on a cushion
of air. Allow trolley to go along the track at a constant velocity (give it a gentle push), the card of known length
(e.g. 0.1m) cuts the light gate beam so the timer records how it takes to travel 0.1 m. The velocity is calculated
from the formula is velocity = displacement / time. The displacement is the length of the card. Repeat the
experiment for different constant velocities.
Timer
123
Linear air track
Card
Light gate
Trolley
Exp. To measure constant acceleration
Rem. Linear air track, trolley, light gates, card, timer. Friction is overcome because the
trolley rides on a cushion of air. Slope the track to give the trolley a constant acceleration.
The first light gate measures the time for the initial velocity u and is calculated by u = L/t1
where L is the length of the card. The second light gate measures the final velocity v and is
calculated by v=L/t2. The distance between the light gates (s) is measured. The acceleration
is then calculated by the formula in the box
a=
v2- u2
2s
Timer
123
Linear air track
Card
Light gate
Trolley
Momentum = mass x velocity (kgms-1)
mass = measure of the ability of a body to resist changes in velocity. (kg).
Conservation of momentum: in a closed system for any interaction, the total momentum before the interaction =
the total momentum after the interaction.
Exp. To verify conservation of momentum.
Rem: powder track, two trolleys, sulphur, magnets. Slope the track to get a constant velocity. Sprinkle sulphur on
the track. Place one trolley at rest in the middle of the track. Allow the other trolley to crash into it at a constant
velocity. The trolleys stick together. Measure the velocity of trolley 1 before the collision and the velocity of
trolley 1+ trolley 2 after the collision. Repeat with different masses on the trolleys.
m1u1= (m1+m2)v, where u= the velocity of trolley 1 before the collision, m1 is the mass of trolley 1 and m2 the
mass of trolley 2 and v the velocity after the collision.
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Timer
Verifying conservation of momentum
123
Card
Trolley 1
Light gate
Linear air track
Trolley 2
at rest
Force is that which causes acceleration. (N)
Laws of motion
 Velocity of a body is unchanged unless an external force acts on it.
 Force  rate of change of momentum. F=ma also (mv-mu) / t
 In any interaction the force on A by B is equal and opposite to the force on B by A.
Gravity: The force between two bodies a distances d apart with a mass of M. G is the
GM1 M 2
universal gravitational constant.
F=
Weight is the force of gravity on a body (N). For a point on the earth's surface w= mg where g
d2
is the acceleration due to gravity. g= GM/d2 where M is the mass of the body and d is the
distance from the centre of the body.
Exp. To verify a  F/m
Rem: Linear air track, light gates, timer, trolley, card metre stick, pan and weights. Friction is overcome because
the trolley rides on an air cushion. Total mass = mass of the trolley + mass causing the force. Part1 Keep the mass
constant. measure the acceleration by: the first light gate measures the time for the initial velocity u and is
calculated by u = L/t1 where L is the length of the card. The second light gate measures the final velocity v and is
calculated by v=L/t2. The distance between the light gates (s) is measured. The acceleration is then calculated by
the formula a = (v2 – u2 )/2s. Repeat for different forces by transferring mass from the trolley to the pan (so as to
keep the mass constant). Draw a graph of a against F.
Timer
123
Card
Light gate
a/ms-2
Linear air track
Trolley
Pan with
weights
F/N
Exp. To measure the acceleration due to gravity.
Rem: timer, metal ball and trapdoor,
electromagnet gate. Attach the gate and
trapdoor to the timer. Measure the
Electromagnet
distance s between the gate and the
trapdoor. Allow the ball to fall through
Ball
the trapdoor and record the time.
bearing
Repeat for different distances s. Graph s
against t2. The slope = ½g.
Switch
S/m
Timer
Friction is the force due to two surfaces
rubbing off each other. The rougher the
Trapdoor
t 2/s2
surfaces the greater the friction. Friction
Graph for g
Measuring acceleration due gravity (g)
can be reduced by lubricants or
polishing. Friction is useful as we could not walk or run or brakes would not work without friction. However
friction causes moving parts to wear ( in engines for example).
Moment (T) = force x perpendicular distance from the turning point of a lever. Equilibrium is when the
acceleration on a body is zero. Principle of moments (law of the lever) : when a body is in equilibrium the sum
of the moments about any axis of forces is zero. Note: clockwise taken as positive and anticlockwise as negative.
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Exp. To verify the principle of moments
Verifying the principle of moments
Rem: metre stick, weights, spring balances, retort
stands. Set up as shown in the diagram. Adjust the
Spring balance
weights until the metre stick in horizontal equilibrium
(balanced). Choose any point to calculate the
Metre stick
clockwise and anticlockwise moments about.
Remember to include the weight of the metre stick.
The sum of the clockwise moments and the sum of
anticlockwise should equal to zero. This verifies the
Mass
Principle of moments.
Lever: a rigid body free to move about a fixed point
called the fulcrum. E.g. spanner, wheelbarrow.
Couple: a system of forces that have a turning effect only.
Pressure = force per unit area. (pa) P=F/A. Measure pressure using a bourdon gauge. Pressure in a fluid depends
on depth and density (P=gh).
Density is mass per unit volume (kg/m3). =m/V
Atmospheric pressure varies with altitude, due the gas blanket around the earth., measured using a mercury or
an aneroid barometer. Atmospheric pressure can be demonstrated by removing the air from a can with steam,
then seal the can and allow it to cool creating a vacuum and the sides collapse inwards. An aneroid barometer
that measures height is called an altimeter.
Boyle’s Law states that at a constant temperature the volume of a fixed mass of gas is inversely proportional to
the pressure. P  1/V or PV = k. When doing calculations the formula P 1 V1 = P2 V2
To verify Boyle’s Law
Rem: Boyle’s law apparatus. Set up the apparatus as
shown in the diagram. Note the pressure and the
volume of the gas. Use the pump to change the volume
and the pressure of the gas. Note the new readings.
Repeat the procedure to get five or six values of the
pressure and the volume. Draw a graph of the pressure
against 1/V. A straight line graph proves that p  1/V.
Note if you multiply P x V you should get a constant.
P/pa
Gas
Pressure
gauge
Archimedes’s principle states that when a body is
To
partially or wholly immersed in a fluid the up thrust =
pump
the magnitude of the weight of the fluid displaced. Law
of floatation: weight of a floating body = weight of the fluid displaced. Hydrometer
= a device for measuring the density of liquids, based on the law of floatation. Rem.
1000000 cm3=1m3.
Boyle’s Law Apparatus
Work is done when a force moves an object. W=F.s (J) 1J=1Nm.
Energy is the ability to do work (J), many forms of energy.
Conservation of energy: in a closed system the total amount of energy remains the same. Kinetic Energy:
Ek=½mv2. Potential Energy: Ep= mgh.
For falling bodies the total energy Ek+Ep=0. Einstein's energy mass equivalence states E=mc2.
Power is the rate at which work is done (w).
Power output
P= W/t 1 watt=1J/s.
X 100
Percentage efficiency =
Efficiency Machines like electric motors etc.
Power input
are not 100% efficient that is the power input is
not equal to the power output.
Addition of vectors
 Vectors that lie in a straight line may be added algebraically, one direction must be chosen a positive .
 Vectors not in a straight line must be added using the triangle or parallelogram law.
 Triangle Law: when two vectors nose to tail form two sides of a triangle their resultant is the
third side
 Parallelogram Law: when two vectors tail to tail form adjacent side of a parallelogram their
resultant is the diagonal.
 NOTE: if right angles are not involved than the sine and cosine rules must be used.
1
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Resolution of vectors is break a vector into its x and y components at right angles to each other. x=vcos and
y=vsin
Angular velocity:  =/t i.e. the rate of change of angular displacement w.r.t time. (rad/s). Angle  = length of
arc/ radius. Connection between linear speed and angular speed is v(linear speed) = r(know how to derive).
Centripedal acceleration: a = r2 or a v2/r (know how to derive). Centripetal force: F=mr2 or m v2/r .
Satellite motion: put centripetal force = to the gravitational force. v2= GM/R.
T(period of the satellite) = 2R/v and T2 =42R2/v2 substitute in for v2.
2
r3
T
2
3
1
Kepler's Law. Relationship between period of and its radius is T  r i.e.
1
=
For a geostationationary orbit i.e. a satellite orbiting above the equator above a
2
T
r3
fixed point there is only one height above the Earth possible. The period has be
2
2
24 hrs and so using the equation T 2 =42R2/v2 the height above the Earth has
to be 36,000 km (h=R-radius of the Earth).
Elasticity and elastic limit
Many objects change shape if a force is applied to them e.g. a spring being stretched. If spring is not over
stretched the it returns to it’s original shape when let go. If is does not return to it’s original shape then it has been
stretched beyond it’s elastic limit.
Hooke’s Law states that when an object is bent, stretched or compressed by a displacement s, the restoring force
F is directly proportional to the displacement – provided the elastic limit is not exceeded. F= - ks . Any system
that obeys Hooke’s Law will execute simple harmonic motion (S.H.M.) e.g. a pendulum swinging at a small
angle, the prong of a tuning fork vibrating. The frequency of the oscillation is f = 1/T (T is the period).
Period T = 2
l
g
Simple
Pendulum
Simple Harmonic motion is motion of a particle whose acceleration towards a
particular point is proportional to its displacement from that point a = -2s,
where 2 is a constant. The negative sign is because a and s are always in
opposite directions.
Period of S.H.M. is the time interval between the moment a particle passes a
particular point in a particular direction and the moment it passes this point
again going in the same direction. T = 2/.
Exp. To measure g using a simple pendulum
Rem: pendulum bob, stand, clock and metre stick. Measure the length of the pendulum
l. Measure T by finding the time for 50 oscillations and  by 50. Repeat for different
pendulum lengths. Draw a graph of l against T 2. The slope x 42 = g.
Wave Motions
l/m
T2
2
S
wave (mechanical wave) = means or transferring energy through a medium without any net movement of the
medium.
amplitude(A) = maximum displacement of a wave from its rest position (m)
Period (T) = time for a point to undergo one oscillation (s).
Frequency (f) = number of oscillations per second (Hz).
Speed (c) = frequency (f) x wavelength ().
Wavelength () = distance between any two successive points in phase (m).
Transverse waves: waves whose movement is at right angles to the oscillation of the medium. Longitudinal
waves: waves whose movement is in the same direction of the oscillation of the medium. Reflection of waves
occurs when they bounce of an obstacle in their path.
Diffraction occurs when a wave front is distorted by an obstacle. The amount of diffraction depends on the size
of the  compared with the obstacle or opening. Interference occurs when two or more waves meet, they tend to
cancel each other out or enhance each other. Constructive interference is when to wave pulses meet and add
together. Destructive interference is when two wave pulses meet and cancel each other out. An interference
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pattern is produced when two coherent sources meet. Coherent sources are sources, which have the same
frequency and are in phase with each other. Maximum disturbances of a wave are called antinodes and minimum
disturbances of a wave are called nodes.
Stationary wave: this is a special case of interference. which happens when two wave of the same frequency and
amplitude going in opposite directions meet. Beats occur when two wave of almost the same frequency meet.
They gradually fall in and out of phase.
Waves can be reflected and refracted obeying the laws of both.
Resonance is the transfer of energy between two bodies, which have the same natural frequency. Important in the
construction of bridges and buildings etc. e.g. buildings in an earthquake, sound produced by our vocal cords.
Polarisation (transverse waves only is when the vibrations of the wave are restricted to one direction only due to
passing through a narrow slit. Light can be polarised. How would you show this.
Doppler effect is the apparent change in frequency of wave due to
the motion of the source of the wave, applies to light and sound. F is
f’ = fc
f’ = fc
the frequency of the source, u is the speed of the source, c is the
( c-u )
( c+u )
speed of the wave and f’ is the apparent frequency. u is positive if
the source is moving away the observer and u is negative if source is
moving towards the observer..
Corpuscular
theory:
Newton
suggested light was made of tiny particles, which when they struck
light waves
the retina caused the sensation of sight. Theory can explain reflection only. Predicted light would
be faster in a denser medium that is now known to be wrong.
Wave theory: Proposed by Huygens, Young showed light exhibited interference and diffraction effects, 
wave. Young's exp. monochromatic light source, two slits, and a screen, found bright and dark lines on the screen
due to constructive and destructive interference. Formulas, n=d sin and n=dx/D apply. n=the order of the
image, s = the width of a slit, x is the distance from the central fringe to the nth fringe and D is the distance of the
slits from the screen . Diffraction grating: large number of parallel lines ruled on a sheet of transparent
material, act as a series of parallel slits. Bright fringes much further apart than for Young's slits. Same formulas
apply.
Exp. To the measure the wavelength of monochromatic light.
Rem: spectrometer, sodium lamp, diffraction grating. Place the lamp in front of the collimator and the diffraction
between the collimator and the telescope. Adjust the width of the collimator slit until a sharp image is formed.
Measure the angle for the bright fringe furthest out if this it the third bright fringe starting with o then n=3.
Measure the angle for the same fringe on the opposite side. Find the angle 2 and  2. Repeat this for each value
of n and get the average .
Dispersion is the breaking up of white light into its constituent colours, a prism is used to do this. A system of
lens and a prism are needed to get a pure spectrum. Primary colours red, green and blue. Secondary colours
yellow, cyan and magenta, got from mixing of primary colours. Complementary colours are two colours that
give white light when mixed. e.g. yellow and blue.
Electromagnetic spectrum: consists of -rays, x-rays, uv, light, i.r., microwaves and radio waves. All have a
common house i.e. oscillating electric charges. All have the same speed. 3 x10 8 ms-1 I.r. has a heating effect due
to electron movement within atoms, it can effect photographic plates and can pass through fog and mist making it
possible to take photographs is such conditions. U.V. is also from electron movements in atoms but at >>
temperature. It causes certain substances to fluoresce, is blocked by ordinary glass, produced vitamin D in the
skin and cause sun-tan. Can cause skin cancer.
Sound Waves
Sound is a form of energy, due to something vibrating has a wave nature, and shows interference effects that can
be shown using two loudspeakers and a signal generator. If you walk along the line between the speakers the
loudness of the sound goes up and down. Sound waves travel around corners that is evidence of diffraction.
Transmission of sound: vibrating objects cause alternate compression and rarefaction of the air molecules which
cause the eardrum to vibrate which in turn send a signal to the brain. Sound must have a medium to travel in.
Reflection/refraction of sound: refraction of sound is apparent on a cold night, sound travels in colder air, so
the sound is continuously refracted towards the ground. Reflection of sound can be shown using a signal
generator and a microphone. You can bounce the sound waves off the wall and pick up the reflections with a
microphone connected to an oscilloscope.
Harmonics are frequencies that are multiples of a fundamental frequency. Important in relation to stationary
waves on a string , f = fundamental frequency (1st harmonic) 2f (2nd harmonic) = 1st overtone, 3f (3rd harmonic =
2nd overtone and so on.
In a pipe closed at one end when sound waves travel in it (produced by a tuning fork for example) at certain
lengths resonance occurs and a stationary waves is set up. A node is formed at the bottom of the pipe and an
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antinode is formed just above the top of the pipe. The simplest stationary wave possible is when the length of the
pipe is l = /4.
For stationary waves in a pipe closed at one end only odd numbered harmonics can be present i.e. f , 3f, 5f etc.
For stationary waves in a pipe open at both ends all harmonics are present i.e. f, 2f, 3f etc.
Exp. To investigate the variation of the fundamental frequency of a stretched string with length.
Rem: sonometer, tuning forks and weights, set the tension constant. For each frequency of tuning fork adjust the
length of the wire until the wire resonates, use a paper rider for this. Graph f against 1/l.
1 T
2
l
f/Hz
frequency of a stretched string formula
Factors that determine the fundamental frequency of a string.
1 (M )
 The fundamental frequency of a vibrating string is when there is an antinode at its
centre and a node at each end.
 The frequency depends on, the length of the string., the square root of the tension and the mass per unit
length. (see formula above)
Exp. To measure the speed of sound in air.
Rem: resonance tube, graduated cylinder and tuning forks. Fill the
cylinder with water. Strike a tuning fork of known frequency and hold
Measuring the speed of sound in air.
above the resonance tube in the water. Raise the tube until the loudest
sound is heard. Measure the distance from the water level to the top of
Tuning fork
the tube. Repeat for different frequency tuning forks.  = 4(l + 0.3d)
Resonance
where d is the diameter of the tube. Use c=f to find the speed. Note:
tube
the antinode is slightly above the tube hence the 0.3d correction to .
The speed of sound depends on the nature of the medium, a fact used
Water
in the search for oil. Ultrasonics are vibrations above audible
Graduated
vibrations, used in medicine to examine the brain or a pregnant
cylinder
women, greater than 20 kHz.
Sonar: send out a wave of a known frequency, measure the time for it
to return. Used to map the sea-bed for example.
The Intensity of a sound at a point = the rate at which energy is
crossing a unit area perpendicular to the direction of the sound (Wm-2). Sound intensity = Power/area i.e. I =
P/A. The threshold of hearing is the smallest sound intensity detectable by the average human ear at a frequency
of 1kHz, its value is =1x10-12Wm-2
The ear is most sensitive to frequencies of between 2000 and 4000hz.
The sound intensity level is measured in decibels (dB). A sound level meter is used to measure sound intensity
levels. Deafness due to exposure to loud sounds is incurable, so ear protection should be worn where the sound
level is above 85 dB. A sound level meter is used to measure sound intensity in decibels. The decibel scale is
used because it is adapted for the human ears response. Doubling the sound intensity increased the sound
intensity level of 3 dB.
Heat and Temperature
The temperature of a body is a measure of how hot it is. Temperature Scale: For the Celsius scale two fixed
points are needed (or any other scale), freezing point of water and the boiling point of water. The length of a
column of liquid, the volume of a fixed mass of gas, the resistance of a conductor are proportional to the
temperature. Any physical property of a substance, which varies with temperature, is called a thermometric
property.
Thermometers: Mercury thermometer, alcohol thermometer (v. sensitive) based on length of a column of liquid.
Platinum thermometer based on resistance as the temperature goes up R goes up, range -200 to 1200 oC.
Thermistor thermometer more accurate than platinum, as the temperature goes up r goes down (semi-conductor).
Thermocouple thermometer, two metals joined., two junctions as different temperatures causes an e.m.f. to be
produced, range -250 to 1500oC..
Lch..8 as 24
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Exp. To calibrate a thermocouple thermometer.
Rem: mercury thermometer, ungraduated alcohol thermometer, ice. Set up as shown
in the diagram. Place the two thermometers in melting
Unmarked
Mercury
ice. Record the temperature on the mercury
Alcohol
thermometer
thermometer
thermometer and measure the length of the column of
alcohol in the alcohol thermometer when columns stop L/cm
Beaker
moving. Heat the water, when the temperature has risen
about 10 oC, mark the level on the alcohol
Wire
thermometer. Repeat this for six more values. Plot a
gauze
graph of length of the alcohol column against
temperature.
T
o
Tripod
.
C
Standard Temperature and Pressure: 273 K and 1.01x105pa (76cm Hg)
Bunsen
burner
Heat Heat capacity = the heat energy needed to change the temperature of a
substance by 1 k (oC)measured in J K-1 .
Specific Heat Capacity = the amount of energy which will change the temperature
of 1 kg of a substance by 1 K. Supplying heat or doing work that increases the internal energy raises the
temperature. The internal energy of a body is the sum of the potential and kinetic energy of its molecules. The
specific heat capacity (c) = Q/m x 
Exp. To find the specific heat capacity of water
Rem: calorimeter, heating coil, joule meter, battery,
Water
123
insulation and thermometer. Find the mass of the
Mercury
calorimeter and the mass of the water, the water must
thermometer
Joulemeter
cover the heating coil. Note the temperature of the
To power
water. Allow current to flow for 10 minutes. Note the
supply
Beaker
final temperature of the water and the energy supplied
Insulation
on the joule meter. Find c from the equation energy
Heating
supplied Q = mwCww+McalCcalcal.
coil
The specific latent heat is the energy supplied during
a change of state, the temperature remains constant.
e.g. solid to liquid.
Latent heat = the heat energy need to change the state
Measuring the specific heat capacity of water
of a substance without a change in temperature. E.g.
solid to a liquid.
The specific latent heat (l) is the amount of energy that will change the state of 1 kg of a substance. l=Q/m.
Water evaporating form the surface of your body takes in latent to evaporate thus cooling you down.
A heat pump is a device which transfers energy from a cold body to a warmer one, reversal of the normal
heating process, used in refrigerators. It works by pumping a liquid with a high specific latent heat and a low b.p.
around a closed system, with a valve to make the pressure on one side of a compressor much greater than the
other. The liquid passing through the valve vaporises absorbing latent heat from the cold surroundings and the
vapour is compressed to release latent heat to the warm surroundings.
Exp. To measure the specific latent heat of vaporisation of water
Rem: calorimeter, thermometer, insulation and
water. Find the mass of the calorimeter and the
water, the initial temperature of the water. Heat
water in a flask to boiling and allow the steam
to pass in the calorimeter with water via a tube.
After some minutes find the final temperature
Wire
gauze
of the steam, water and calorimeter and the
mass. Energy lost by the steam = energy gained
by the calorimeter and energy gained by the
water. Find l from: msteamCsteamsteam+
msteam lsteam = mwCww+McalCcalcal
Measuring the specific latent hear of vapourisation of water
Flask
Insulation
Water
Steam
Tripod
Bunsen
Lch..9 as 24
Stream
trap
Mercury
thermometer
Beaker
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Exp. To measure the specific latent heat of fusion of ice.
Rem: calorimeter, insulation, thermometer and ice. Find the mass of the calorimeter, water and ice, the initial
temperature of the water and the calorimeter. Add the ice and when it is melted find the final temperature of the
ice, calorimeter and water. Energy gained by the ice = energy lost by the calorimeter + energy lost by the water.
Find l from :
miceCiceice+ mice lice = mwCww+McalCcalcal
There are a 3 ways of transferring energy, (a) conduction = transfer of energy through a substance without the
movement of the molecules, (b) convection transfer of energy by movement of heated molecules, (fluids only)
and (c) radiation transfer of energy between two points by electromagnetic waves. Note metals are good
conductors of heat, liquid and gases are not. Remember the importance of insulation for the conservation of
heat. The U-value of a substance is the rate at which energy is conducted through a substance for a give
temperature difference between the two sides. The solar constant is the amount of energy falling normally on a
unit area of the earth's atmosphere per second when the earth is at its mean distance from the sun.
Electricity current and static
Electrostatics
There are two type of electric charge positive and negative. Normally bodies are electrically neutral. When
electrons are lost a body becomes positively charged and when electrons are gained a body becomes negatively
charged. Explanation from the theory of atoms, protons neutrons and electrons. The laws of charge are like
charges repel and unlike charges attract.
Van De Graff Generator: Consists of pulleys with a belt to transfer charge to a metal dome via sharp metal
combs, based on point effect.
Gold leaf electroscope: Consists of an insulated metal cap attached to a rod with gold leaf in a metal case with a
glass window. Used to detect a charge, find out if a substance is a conductor or an insulator and find if a charge is
positive or negative. (Know diagram).
Two ways to charge: A) Friction, rubbing two surfaces together. B) Induction, forcing a charge from one body
onto another. (Must know how).
Conductors allow charge to flow, they have free electrons. Insulators do not allow charge to flow, all their
electrons are tightly bound. Earthing is when a charged body is connected to the ground via a conductor.
Charging by induction: Charge body A, bring it close to body B(conductor), earth B by touching it, remove A.
B is now charged oppositely to A. Explained by movement of loosely bound electrons.
Everyday effects of static electricity: crackling and clinging of clothes, build up of charge on television
screens, sparks produced by static electricity can cause explosions in oil refineries and flour mills due to vapours
and fine dust.
Coulomb's Law: the force between two point charges is proportional to the product of the charges and inversely
proportional to the square of the distance between them. (like gravity). The direction of force depends whether
the charges attract or repel each other.
Coulomb's Law
1
Q1Q2  is the permittivity of the medium i.e. a measure of the resistance of the medium the
electric force between the charges. As  goes up the force goes down. r is the relative
F = 
r2
permittivity which is = is /o, i.e. the ratio of the permittivity to the permittivity of free
space (o).
Point effect: charge concentrates at a point, it is not evenly distributed on an irregular body. If the concentration
of charge at a point is high enough then it will ionise the air molecules around it, causing a discharge. Lightning
conductors and the van de Graff generator are based on this.
An electric field is the region in which electric charges experience a force, the directions of the lines of force are
positive to negative. (like magnetism). Electric fields are used in electrostatic precipitators to remove smoke from
chimneys, photocopying, the light removes electric charge form the drum
Electric field intensity
and toner is attract to the charged areas giving an image of the original.
F
How could you demonstrate an electric field?
E= Q
E is vector quantity (NC-1)
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Electric field strength E = force per unit charge at that point, i.e. the force
per colomb. The number of lines of electric force passing through any given
area perpendicular to the force.
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A Potential difference (p.d.) exists between two points when work is done bringing a unit charge from one point
to the other. W=VQ. Unit = volt 1V=1J/1C. A p.d exists if there is a difference in the level of charge between
two points. The greater the electric field strength the greater the voltage. An electronvolt is the energy gained by
an electron being accelerated through a p.d. of 1V. 1eV=1.6x10 -19J. The earth is taken to be at zero potential,
used a reference just like the B.P. of water for thermometers. Potential can be measured using a gold leaf
electroscope, voltmeter or an oscilloscope. All points on a conductor carrying a static charge are at the same
potential.
Electromotive force (e.m.f.): In any closed loop the work done in carrying a unit charge around the loop. The
e.m.f. of a battery is a measure of the force available to push charge around a circuit, measured in volts. Sum of
the individual p.d.'s in a circuit = e.m.f.
Capacitance is the ratio of charge to potential. i.e. C=Q/V (F). one farad (F) is the capacitance due to the
addition of a charge of 1 Colombo raising the potential by 1 volt.
The capacitance of a charge conductor is increased by bringing an oppositely charged conductor or earthed
conductor near it.
Parallel plate capacitor: A device for storing charge, consists of two parallel plates oppositely charged with an
insulating material (dielectric) between them. The capacitance of a parallel plate capacitor C= A/d, A is the
common area of the plates and d is the distance between the plates.
Energy in a charged capacitor: W=½CV2 or W=½Q2/C (know how to derive)
Practical capacitors: variable capacitor: two sets of plates, one set can be rotated in/out of the other, used for
radio tuners. Fixed capacitors: named according to the dielectric used. e.g. plastic foil, to sheet of aluminium
interleaved with two sheets of plastic rolled up. Uses of capacitors: separate a.c. from d.c., operate a switch after
a period of time and tuning circuits, camera flash.
Switch 1
Charging a capacitor
Closing switch 1 charges the capacitor, and then opening switch 1
and closing switch 2 discharges the capacitor through the l.e.d.
showing capacitors store energy.
Switch 2
L.e.d.
Capacitor
Charging and discharging a capacitor
Exp. Investigate the factors affecting a parallel plate capacitor
Connect one plate to an electroscope and charge with a 2kV supply, Earth the other plate. The deflection of the
leaves is a measure of the potential between the plates. Varying the common area between the plates while
keeping the distance constant shows as A goes down V goes up so C goes down and vice versa. so A  C. Now
keep A constant and varying d shows as increases then V goes up and C goes down and vice versa, so C1/d.
The proportionality constant depends on the material between the plates ( the dielectric). so C= A/d.
Electricity
An electric current is the flow of charge or electrons. The ampere is that constant current which if maintained in
two straight parallel conductors of infinite length and negligible cross-sectional area one metre apart in a vacuum
causes each to exert a force of 2 x 10-7N/m length on the other. One coulomb = 1 amp for 1 sec. i.e. Q=It. To
measure current the ammeter must always be put in series in a circuit.
The sum of the currents flowing into a junction = to the sum of the currents leaving the junction.
Electrical conductors allow charge to flow easily and electrical insulators do not
allow charge to flow.
Electric current has three effects, (a) heating effect, (b) magnetic effect, (c) chemical
effect.
Voltages in series are added together i.e. V=V1 + V2 + V3 and so on. Voltages in
parallel with each other are the same i.e. V1 = V2 = V3 and so on. Voltage is measured
using a voltmeter in parallel with the part of the circuit whose p.d. is to be measured.
Cells (batteries) are devices for storing chemical energy and releasing it as electrical
energy in a circuit. Primary Cells cannot be recharged, chemical reaction cannot be
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reversed. e.g. the dry cell. Secondary Cells can be recharged, the chemical reaction is reversible, e.g. lead-acid
cell, lead dioxide anode, lead cathode and dilute sulphuric acid electrolyte. The voltage of batteries connected in
series is the sum of the individual voltages.
Power = voltage x current measure in watts (w)
Resistance is something that slows down or stops the flow of current. A resistance of 1 results when a current
of 1A flows for a potential of 1V. Resistance is measured using an ohmmeter or a an ammeter and voltmeter and
then using the formula R=V/I
Resistor in series: RT=R1+R2+R3+............
Ohm's Law states that at a constant temperature the current is proportional to the potential difference between
the ends of a conductor. i.e. V/I=R.
Exp. To prove Ohm's law
Set up a circuit as shown in the
V
Ohm's Law
diagram. Record the voltage and
V
the current. Repeat these
measurements each time varying
V
the voltage using the rheostat.
Ohm's Law
Graph V against I.. The slope is
A
Circuit
the resistance. The graph for
ohm’s law is the same graph as
I/A
for the variation of current with
voltage for a metallic conductor.
Resistors in parallel:
1
1
1
1


 
R T R1 R2 R3
Variable resistors (rheostats): resistors whose resistance can be varied.
Resistance and temperature
 For metallic conductors as the temperature
increases the resistance increases
 For semiconductors (or insulators) as the
temperature increases the resistance decreases.
Factors affecting resistance of a conductor
 The temperature
 The length of the conductor
 The cross-sectional area
 The material the conductor is made off
(resistivity).
To ohmmeter
Coil of wire
Mercury
thermometer
R/
Glycerol
Beaker
Water
Wire
gauze
Tripod
Exp. To find the variation of resistance of a copper wire (metallic
T/ oC
conductor) with temperature.
Rem: copper wire, glycerol, thermometer, ohmmeter, Bunsen and
beaker. Place a copper wire in glycerol in a test tube and place
this in a water bath. Measure the resistance R , and the
temperature T . Heat and measure R for different temperatures and graph R against T.
Exp. To find the variation of resistance of a thermistor
(semi-conductor) with temperature
Rem: thermistor, thermometer, ohmmeter, Bunsen and
beaker. Connect the thermistor to an ohmmeter, and place
in a beaker of water. Heat and measure R for different
temperatures. Graph R against T.
Exp. To measure the resistivity of a wire.
Take a metre length of nichrome wire and measure it's
resistance (R) using an ohmmeter, measure the length (l)
accurately. Remember to measure resistance of the leads
and subtract this. Measure the diameter using a
micrometer, repeat this and get an average. Calculate the
Bunsen
Resistance of metallic conductor v’s temperature
To ohmmeter
Thermistor
Mercury
thermometer
R/
Glycerol
Beaker
Water
Wire
gauze
Tripod
T/ oC
Bunsen
Lch..12 as 24
Resistance of thermistor v’s temperature
Athdhéanamh Fisice
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radius (r) and then the cross-sectional area (A=r2). Calculate the resistivity () from the equation =RA/l
Potential divider Circuit = a device for obtaining a lower p.d. from a higher p.d. Taking the voltage off
different resistors splits the supply voltage. The sum of the voltages across the resistors = the supply voltage.
Potentiometer = a device for measuring p.d. accurately.
Wheatstone bridge: accurate circuit for determining
resistance., the metre bridge is a practical version of
R1 l 1
this.
The Wheatstone bridge is a temperature
R2 l 2
controlled device, as a change in resistance due to heat affects
the balance causing a current to flow. This current can be used
to switch on or off a circuit. A wheatstone bridge is used for
fail-safe devices. E.g. to shut off the fuel if the pilot flame goes
out in a gas boiler.
Wheatstone Bridge Circuit
R1
R2
l1
l2
Joule's Law: The rate at which electrical energy is converted into internal energy in a resistor is proportional to
the square of the current flowing through it. i.e. P  I2 or P=VI or P=RI2
Exp. To verify joule's law
Set up as shown in the diagram. Allow a constant
current to flow for 5 minutes and record the
2
I
temperature. Repeat for different current values. Graph
A
I2 against the temperature .
A2
1 kW h = the amount of electrical energy converted
into other forms in one hour. Cost of electricity = no. of
kW h x price per unit.
Total power in an electrical system is P=VI, power lost
Water
o
as heat P= RI2, therefore to reduce power loss increase
/ C
V and reduce I.
Domestic Electricity: Prevent an electric shock by
Coil
earthing, protect a device using a fuse, which if
overloaded blows. Fuse chosen according to maximum
Insulation
current of the device. Know house circuit diagrams for
lights, sockets.
Chemical effect of electricity
Electrolysis = conduction in a liquid causing chemical reactions. Electrodes are the carbon or metal plates by
which current enter/leaves the liquid. Electrolyte = liquid which conducts electricity. Anode = positive
electrode, cathode = negative electrode. Ions = atoms or molecules which have lost or gained electrons and these
are the charge carriers in an electrolyte. Voltameter = whole arrangement of electrolyte and electrodes.
Active Electrodes: Take part in the chemical reaction an obey ohm's law. Inert Electrodes: Do not take part in
the chemical reaction; do not obey ohm's law, because I/A
I/A
a reaction that tends to oppose the current must be
overcome. e.g. hydrogen on the cathode in the
electrolysis of dilute HCl. This can be investigated by
V/V
V/V
electrolysis of copper electrodes (active) in copper
sulphate solution and with carbon electrodes (inert) in Active electrodes Inert electrodes
copper sulphate solution and plotting a graph of I
against V in each case.
The chemical effect of an electric current is used in electroplating, extracting metals from their ore e.g.
aluminium, purifying metals, e.g. copper and making certain types of capacitors.
Electroplating is the use of electrolysis to coat one metal with another metal. e.g. chrome plating.
Relationship between current and voltage for different conductors
1. For metallic conductors the current is proportional to the voltage, obeys ohm’s law, electrons are the
charge carriers.
2. For a filament bulb the current is not proportional to the voltage, electrons are the charge carriers.
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3.
For semi-conductors the current is not proportional to the voltage, electrons and positive holes are the
charge carriers.
4. For ionic solutions (electrolytes) if the electrodes are active (they take part in the chemical reaction)
the current is proportional to the voltage and it obeys ohm’s law. If the electrodes are inactive the
voltameter behaves as a cell and this emf must be overcome first and then the current is proportional to
the voltage. The charge carriers are positive and negative ions.
5. For gases to conduct they must be ionised. This is done in a discharge tube, two metal electrodes and a
gas at low pressure. At low voltage many ions recombine before reaching the electrodes,  low I. As
the p.d. goes up all the ions reach the electrodes, the I becomes independent of the p.d. Increasing the
p.d. more gives the ions enough energy to ionise other molecules giving an avalanche effect and I begins
to rise rapidly. At high voltage or low pressure the gas emits electromagnetic radiation, the colour
depends on the gas (glow discharge). e.g. sodium gives a yellow glow. The
I/A
charge carriers are positive and negative ions and electrons.
6. For a vacuum initially the current is proportional to the voltage until all the
electrons produced by thermionic emission from the cathode cross the tube and
further increase in voltage result in no increase in current.
Exp.To investigate the variation of current with
V/V
Current v’s Voltage for a vacuum
p.d (V) for a filament bulb
I/A
Set up as shown in the diagram. Record the
mA
current for a voltage of 1V. Repeat and record
the current for different voltages. Graph I
V
against V.
Exp.To investigate the variation of current with
p.d (V) for a copper sulphate solution with
copper electrodes
Current v’s Voltage for a filament bulb
V/V
Set up as shown in the diagram with copper
A
electrodes (active) in copper sulphate
solution. Record the current for a voltage of
1V. Repeat and record the current for
I/A
different voltages. Graph I against V.
V
Copper anode
Copper
Semi-conductors
cathode
Semi-conductors have resistivities between
conductors and insulators e.g. silicon (Si) and
Copper
Beaker
germanium (Ge). At room temperature Si has
sulphate
solution
one free electron in 1010 atoms, very small.
V/V
Since such a Si atom has lost one of four
Current v’s Voltage for Copper sulphate solution
outer electrons it is effectively positively
charged leaving a positive hole. Conduction
in Si is due to positive holes and free electrons, similar for Ge. This conduction is due the Si only so it is called
intrinsic conduction. As the temperature goes up the resistance goes down. Doping can dramatically increase
the conductivity, that is adding impurities of phosphorus (P) or boron (B) to the pure Si. If P is added it has 5
outer electrons and since only four are needed for bonding with Si one electron is left available for conduction.
The majority carriers for conduction are electrons so this type of Si is referred to as n-type . If B is added to the
Si the an extra positive hole is created as B only has 3 outer electrons for bonding. The majority charge carriers
for conduction are positive holes. This type of Si is referred to as p-type. Conduction mainly due to impurities is
called extrinsic conduction
Light dependent resistor (LDR): Made of CdS, as the temperature goes up due to light the resistance goes
down. Used to switch on/off street lights, light intensity meters, security lights.
Semi-conductor thermistor: Made of oxides of iron,. nickel and cobalt. Very sensitive to temperature. An
increase in temperature leads to a large decrease in resistance. Used for temperature controlled switches.
P-N junction: Junction between n-type and p-type semi-conductor. At the junction electrons drift towards the ptype material and positive holes towards the n-type material giving a neutral layer around the junction called a
depletion layer. In this layer the p-type area is now negative and the n-type area positive giving a p.d. at the
junction. For Si. the junction voltage is 0.6V.
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Junction diode Forward bias: p-type connect to the positive, current flows a positive holes are pushed towards
depletion layer as are the electrons, reducing the depletion layer. Electrons and holes combine losing energy as
heat. Reverse bias p-type connected the negative, attracts positive holes increasing the depletion layer, as are the
electron attracted away for the junction increasing the depletion layer, no current flows. Diode = device which
allows current to flow in one direction only. The variation of current against voltage is called the characteristic
curve of a diode.
Exp. To investigate the variation of current against voltage for semi-conductor (diode).
Set up a circuit as shown in the diagram. Connect the diode in forward bias and measure I (milliammeter) for
stops of 0.1V. Plot a graph of I against V. Repeat for the diode in reverse bias (microammeter) and plot on the
mA
I/mA
+6V
Forward
Bias
0.6V
V
0V
Reverse
Bias
I/uA
same graph.
Rectifier: A common use of the diode is converting a.c. to d.c., one diode give half-wave rectification, four
diodes needed for full wave rectification. A capacitor in parallel smoothes the current.
V/V
t/s
Half-wave rectification
V/V
t/s
Full wave rectification
Electromagnetism
Magnetic fields: Use
the right hand grip rule
to find the direction of
the field.
S
N
Magnetic field line: a
line drawn in a magnetic
field so that the tangent
current
Bar magnet
to it at any point shows
Solenoid
in a straight
the direction of the
wire
magnetic field at that
point.
The magnetic effect of an electric current: Every current that flows in a conductor has magnetic field around it
caused by that current. The diagram above shows the magnetic field patterns due to current in straight wire and a
solenoid. This effect was discover in 1819 by Hans Christian Oersted.
An electromagnet is a solenoid with a soft iron core that loses its magnetism when the current is switched off.
Electromagnets are use in electric motors, electromagnetic relays, and cranes to lift scrap metal.
Earth's Magnetic field: The earth acts as if it had a bar magnet at its centre. Angle of declination = angle
between the geographic N/S and the magnetic N/S.
Force on a current in a magnetic field: A current flowing in a magnetic field experiences a force, basis of
electric motors, moving coil meters and loudspeakers. The force is perpendicular to the current and perpendicular
to the magnetic field. The direction of the current is found using Fleming’s left hand rule. The force on a moving
charge F=qvB (know how to derive).
The force on a current in a magnetic field F=BIl if the current is perpendicular to the field otherwise it is F=BIl
sin,  is the angle between I and the field. The magnetic flux density B (T) is the force per unit current per unit
length of a conductor at right angles to the field. (a measure of the strength of the magnetic force). A current of
1A flowing at right angles to the field experiencing a force of 1N has a magnetic flux density of one tesla (T)
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D.C. Motor : The current flow in the coil causes a torque T = BIAN. Must reverse polarity of the coil every half
turn to keep the torque in one direction. Consists of carbon brushes, coil, magnets and commutator (split ring).
(Know how it works)
The Ampere is that constant current which if maintained in two straight parallel conductors of infinite length, of
negligible cross section and placed 1 m apart in a vacuum, would produce a force on each other of 2 x 10 -7 N per
metre length. This force can be demonstrated by passing a 4A current through two parallel strips of aluminium
foil and they will be seen to move away from each other when the current is switched on.
The Magnetic flux  = flux density B x area A. For a coil of N turns the total flux (flux linkage) = N
Laws of electromagnetic induction
 A change in the flux threading any closed loop causes an induced e.m.f. which is proportional to the rate
of change of flux threading it. (Faraday's Law) E= (final flux – initial flux) / time taken
 The direction of the induced current is always such as to oppose the change causing it. (Lenz’s law)
Generators : Electromagnetic induction is the principle on which an electric generator works. It converts
mechanical energy into electrical energy. The ESB generates electricity by producing steam to rotate large
turbines in magnetic fields to generate electricity. Alternators in cars, and dynamos are generators.
Alternating Current A.C. continually changes direction, completing one cycle in 1/50th of a second. A graph of
I against t gives a sine wave.
Root Mean Square (r.m.s.) values are the effective value of a.c. current and voltage. Ir.m.s.=Io/2 and
Vr.m.s.=Vo/2. Io and Vo are the maximum value of I and V respectively. A.C. can go through capacitors that
block d.c. As the capacitance goes up the a.c. current flow goes up. Use capacitors to block d.c. and control the
size of a.c. like resistors.
Inductance: Current in one coil induces an e.m.f. in another coil nearby = mutual inductance. A coil carrying a
changing current  a changing magnetic field  an induced e.m.f. = self-inductance. Inductors act as resistors
to a.c. as the induced e.m.f. opposes the current.
Inductors have greater resistance to A.C. than D.C. because of back emf. Inductors are used to smooth out
variations in d.c. power supply units, in tuning circuits for radios and dimmer switches used in stage lighting.
N p V p Transformers are devices for changing low a.c. voltage to high a.c. voltage and vice versa. They

have two coils a primary and a secondary. A step up transformer has a greater output voltage than
N s V s input voltage, more turns on the secondary than primary, a step down transformer is the opposite of
this. Transformers work by transferring energy from the primary to the secondary via the magnetic field of the
common iron core. For a 100% efficient transformer P in= Pout i.e. Vin x Iin= Vout x Iout. Transformers are
used to change voltages up or down in generating stations, substations, suitable for transmission and supply to
consumers. Transformers are used in computer, radios, t.v’s etc. to supply the right voltage to the equipment.
Atomic Physics
Electron: Cathode rays discovered c1895, found to be negatively charged. J.J. Thompson measured e/m for
cathode rays, same regardless of cathode material implying the electron is a fundamental particle of matter.
Millikan verified the charge unit is 1.6 x 10-19C (oil drop experiment). Cathode rays are electrons.
Thermionic emission is the emission of electrons from surface of hot metal.
Cathode rays: Travel in straight lines, carry energy, are negatively charged, deflected in magnetic and electric
fields with a charge of 1.6 x 10-19C.
For electrons moving in an electric field the loss in potential energy = the gain in kinetic energy, i.e. eV = ½mv 2
A beam of electrons moving at right angles to a magnetic field moves in a circle.
Cathode Ray Tube: grid controls brightness of the beam, the anodes narrow the beam, the x and y plates control
the position of the beam. The electrons are produced by thermionic emission. The kinetic energy of the electrons
is converted into light by the phosphor coated on the screen. They are used in televisions and computer monitors.
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X-Rays: If a beam of electrons accelerated to very high speeds strike a metal target x-rays are produced
(Roentgen). 99% of the electrons energy is converted into heat. A tungsten target is used. Properties of X-rays
are not deflected by electric or magnetic fields, so they have no charge. They exhibit diffraction and interference
effects, so they have a wave nature. They affect photographic emulsions like light, have a  of 10-10m, and
cause some substances to fluoresce. X-rays penetrate many substances, are absorbed by lead and ionise the
materials they pass through (reason for their danger). Uses of X-rays photographing bones, cancer treatment,
detecting structural faults and monitoring thickness of substances.
Photoelectric Emission: Emission of electrons from the surface of a metal due incident electromagnetic
radiation. It can be investigated using a photocell. a photocell is a device that conducts electricity when light of a
suitable frequency shines on it. The anode is kept positive w.r.t. the cathode so the electrons emitted are attract to
it and flow around the circuit. It is found below a certain frequency (threshold f) no current flows regardless of
the light intensity, also changing the frequency below the threshold does not affect the current.. Above the
threshold f the current  to the light intensity.
Explanation of photoelectric emission:
1. Einstein said that light must be considered to be a stream of packets of energy that he called photons.
2. The energy of a photon depends on the frequency only. E = hf. Where h = Planck’s constant.
3. the brighter the light source the more photons emitted per second.
4. electrons in metals are held with certain forces and the energy needed to remove the most loosely bound
electron is called the work function W of that metal.
5. If E of the photon is less than the work function then no electrons are emitted
6. If E of the photon is above the work function electrons are emitted.
7. The amount of E of the photon above the work function appears as kinetic energy of the electron.
Photoelectric Law: hf =  + ½mv2 (Einstein).  (work function) = hfo(threshold frequency). fo depends on the
metal. A graph of Ek against the f gives a straight line with an intercept at fo.
Uses of photoelectric devices: Some types of burglar alarms, automatic doors, counting items on a conveyor
belt.
Radioactivity
The atom is made up of a nucleus of protons and neutrons (nucleons) with electrons going around the nucleus.
The atomic number (Z) is the number of protons in the nucleus and it distinguishes one atom from the next. The
mass number is the number of nucleons. An isotope is atom of the same element with a different mass number.
Rutherford's experiment: Bombarded gold foil with -particles (dipositively charged He nuclei). He found
most went right through, some were deflected and some came back along their original path. He concluded that
atoms were mostly empty space, with a small dense nucleus at their centres that must be positively charged as
like charges repel.
The arrangement of electrons in an atom:
The idea of electrons are arranged in certain allowed orbits came from Neils Bohr in 1913. Evidence for this
model came from emission spectra.
Emission spectra are due to light given our by solids, liquids or gases supplied with sufficient energy e.g. by
heating them or passing an electric current through them. If this light is passed through a prism (or diffraction
grating ) then an emission spectrum is formed.
1. A continuous spectrum is produced by incandescent solid or liquid, all visible wavelengths are emitted.
They are not characteristic of the material that produces them.
2. Line spectra are produced gaseous elements with sufficient energy to give out coloured light and passing
the light through a prism (or diffraction grating) gives a line emission spectrum. Line spectra are
characteristic of the element (fingerprint of an element). The spectra are viewed through a spectroscope.
Because elements have their own line spectrum light for substances vapourised or light from distances stars and
galaxies can be analysed to find out what elements they contain.
Explanation: When an electron absorbs energy it may move to higher energy orbit. This excited electron moves
back to its original orbit emitting a photon of light energy with a definite frequency and wavelength. It appears as
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a line on the spectrum. E2 –E1 = hf. Because of definite allowed orbits only certain frequencies can be emitted.
Each frequency gives a different line and different atoms have different numbers of electrons so therefore
different excited states possible.
Radioactivity: Becquerel found photographic plate left beside a uranium salt was blackened. Concluded uranium
emits radiation, radioactive. Radioactivity is the spontaneous disintegration of unstable nuclei with emissions of
one or more types of radiation.
Radiation Detectors: Geiger-Muller tube. The tube has a gas at very low pressure with a p.d of 300-400 volts
between the centre wire (positive) and the tube (negative). Radiation enters the tube via a very thin mica window
and ionises some of the gas. The ions are accelerated in the electric field causing more ionisation that is needed
to get a measurable current. The current operates a counter or loudspeaker. To stop continuous discharge a
resistor is put series with the tube that cause a pause in the current. This pause is called 'dead-time'. Counting
devices: A ratemeter gives the number of particles entering the detector per minute or second. A scalar gives the
total number of particles detected.
Types of radiation
Radiation
Nature
Mass/u
Charge/e
Ionising ability
Penetrating
ability
-particles
-particles
-rays
He nuclei
electrons
electromagnetic
radiation
4
0.0005
0
+2
-1
0
good
medium
poor
poor
medium
good
Deflected in
electric/
magnetic fields
yes
yes
no
Exp. To investigate the range of the 3 types of radiation in air.
Rem: Source of ,  and  radiation, detector and counter. Find the background radiation
Ad
-1
count. Place the -source in front of the detector and find the count rate. Repeat for the
s
source at different distances from the detector until the count rate = background rate.
Graph Ad (count rate) against distance. Repeat this procedure for  and -sources.
Nuclear reactions: An unstable nucleus becomes stable by emission of radiation in a
226
222
4
series of steps called a decay chain, represented by equations. e.g. 86 Ra  86 Rn  2 He (
-emission) NOTE the sum of the mass numbers must be both the same on each side of the equation. e.g.
214
214
0
82 Pb 83 Bi  1 e (-emission), NOTE the increase in atomic number, no change in mass. N.B. The total mass
on each side of the equation is slightly different, the loss in mass mainly accounted for by E k of the particles
emitted + -rays. To find the mass converted to energy use E=mc2. This is the equation of mass energy
equivalence.
The activity (A) of a radioactive substance is the number of nuclei of that substance decaying per second.
Law of radioactive decay: The number of disintegration's per second is proportional to the number of nuclei.
d/cm
i.e.
dN
  N
dt
Half-life: T½= time taken for half of the nuclei in a sample to decay. T1
2

ln 2

Ad
s -1
. The
graph opposite shows how half–life is calculated from activity against time graph.
70
35
use the graph to find T½
T
t/s
1/2
Uses and hazards of radiation: Medicine -rays are used to kill cancer cells,
sterilisation, diagnosing disease using radioisotopes.
Industry Can trace the flow of materials, e.g. oil in a machine, can monitor thickness of a substance. Other uses
In agriculture to monitor fertiliser uptake by plants. Finding the age of fossils and rocks i.e. carbon dating, smoke
detectors. Hazards radiation burns, genetic mutations and cancer. -rays are the most dangerous because of their
high penetration. We are all exposed to background radiation due to cosmic rays from space, radioactive
elements in the Earth’s crust and man-made radioactive materials.
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Precautions handling radioactive materials
 Use protective clothing and spend as little time using them as possible.
 Make sure sources of radiation are well shielded.
 Handle using tongs and do not eat, drink or smoke near sources of radioactivity.
The atomic mass unit is mass of an atom compared to carbon 12, it is equal  the mass of a carbon 12 atom.
The Mole is the amount of any substance that contains as many particles as there is atoms in 12 g of carbon 12.
This is 6.02x1023. The atomic mass of any element expressed in grams contains 6.02x10 23 atoms.
Fission: Breaking up of a large nucleus into two or more smaller nuclei of similar size with the release of energy.
Protons and neutrons are held in the nucleus by strong nuclear forces 106 stronger than the electrostatic forces,
but have a very short range. U 235 undergoes fission easily with slow or thermal neutrons.
235
1
141
92
1
Fission Reaction: 92U 0 n 56 Ba 36 Kr 30 n . Large amounts of energy are released. 1kg of U is equivalent
3,000,000 kg of coal. On average 2.5 neutrons per fission reaction. Above a certain critical mass a chain reaction
occurs, i.e. al least one neutron from each fission produces another fission reaction.
Atomic bomb: Two pieces of fissile material less then the critical mass are brought together by a chemical
explosion giving an uncontrolled fission chain reaction.
Fission Reactor: Energy from fission can be used to generate electricity. The rate of fission is controlled so that
on average only one of the neutrons produced causes another fission. Enriched U 235 is used as a fuel. The core
of the reactor contains many control (moderator) rods made of steel containing B or Cd, which raised and
lowered to absorb neutrons and so control the reaction. CO2 gas or D2O used as coolants and their heat produces
steam to drive a turbine and generate electricity. Uranium 238 is not suitable for fission because it does not
undergo fission with slow neutrons, it absorbs the neutrons produced. U 238 needs neutrons of energies greater
than 1 MeV for fission.
0
U10n239
94 Pu 2 1 e
59
1
60
Artificial Isotopes: Uses in medicine, made in reactor cores using stable isotopes. e.g. 27Co 0 n 27 Co
Plutonium is the most toxic substance known to man with a half-life of 24360 yrs.
238
92
Fusion is the joining together of two small nuclei to form one larger one with the release of energy e.g.
2
2
3
1
1 H 1 H 2 He 0 n . This is the type of reaction that occurs in stars like the Sun. The main problem with fusion
so far is the very high temperatures needed for the reaction. It does have the advantages of little pollution and the
an almost unlimited supply of fuel (D2O) in the oceans.
Option 1 Particle Physics
Conservation of Mass-Energy and momentum in Nuclear Reactions
In all nuclear reactions the mass-energy before disintegration and the mass-energy afterwards is the same. The
momentum before the disintegration is the same as afterwards also. The energy released following a radioactive
disintegration is called the disintegration energy (Q).
The neutrino
In nuclear decay processes subtracting the total mass of products from the total mass of reactants gets the change
in mass. This loss in mass becomes kinetic energy of the products. In some  decay disintegrations there was a
discrepancy. This led to the proposal and later discovery of new particle called the neutrino () that accounts for
the missing mass and momentum.
The first splitting of the nucleus artificially
In 1932 John Cockroft (English) and Ernest Walton (Irish) bombarded lithium with accelerated protons splitting
an atomic nucleus in two artificially for the first time. They showed that the loss in mass was equal to the gain in
kinetic energy of the particles after bombardment thus giving the first experimental verification of Einstein’s E
=mc2 equation. Protons were produced in a hydrogen discharge tube an accelerated with a high d.c. voltage,
struck a lithium target at a 45o angle and the products (helium nuclei) were emitted at right angles to the lithium
to be detected on either side of the target.
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7
3
Li 11H  24 He  24He  energy
Athdhéanamh Fisice
D.M.A ©
Particle accelerators
Cockroft and Waltons experiment involved them building the first particle accelerator converting matter into
energy. To convert energy into matter much higher energies were needed. This led to the building of much larger
particle accelerators like the larger one at CERN in Switzerland. It has been found the higher the energy of the
colliding particles the greater the variety of new particles produced and the greater the mass of the particles.
The unified atomic mass unit (u): Masses in particle physics are usually given in u which is = 1.66 x 10 -27 Kg.
Converting Energy into Matter.
Antimatter
1. The positron is the same mass and properties as an electron except it has a positive charge. It is the
antiparticle of the electron
2. Pair production: When energy is converted into matter a pair of particles is always produced, the
particle and its anti-particle. High energy -rays are used to do this. Momentum and charge are
conserved. hf =2 mc2 + Ek1 + Ek2
3. Pair annihilation: If a particle and its anti-particle meet they annihilate each other and energy is
produced. E.g. e+ + e-  2hf (electron positron annihilation)
The fundamental forces of nature
1. Gravitation is a weak force unless the masses involved are very large and it is always attractive. It acts
over an infinite distance. It is the force that keeps planets, stars and galaxies together.
2. The electromagnetic force is the force that binds electrons and protons together in atoms and
molecules. It can be attractive or repulsive and acts over an infinite distance but its size decreases
rapidly with distance. It is 1040 stronger than the
QUARKS
gravitational force.
Name
Name
Name
3. The strong nuclear force is the strongest of the four
-15
Up
u
-e
forces. Its range is very short 10 m. It is responsible for
holding the nucleus of an atom together despite the
Down
d
+e
repulsive electrostatic forces due to the positively charged
Strange
s
+e
protons. Electrons do not experience the strong force.
Charmed
c
-e
4. The weak nuclear force can be felt by all particles when
bottom
b
+e
they are near each other. It acts over a range of 10 -18 m. 
Top
t
-e
decay and the decay of neutron into a proton occur via the
weak force.
Hadrons
Leptons
Feel the weak, electomagnetic
and gravitational forces
Do not feel the strong force
(elementary particles)
Feel all four forces
Mesons
mass between that
of an electon and
proton
Consist of
3 Quarks or
3 Antiquarks
Consist of a
Quark and an
Antiquark
Elementary particles
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Baryons
mass greater than or
equal to the proton
Athdhéanamh Fisice
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Anti-quarks are the named anti-up etc., the symbols have a bar over the letter e.g. anti-up is  and their charges
are opposite to their partner quark so the charge on anti-up is +e. All particles are made up of combinations of
quarks or anti-quarks that are the elementary particles. For example a proton (p) with a charge of +1 (=++-)
is made up of the quarks uud (see quark table)
Option II Applied Electricity
Electromagnetic relay = a switch in an electric circuit
that is turned on or off by an electromagnet Used in car
starting motors, heater fan, horn and rear window
heater, switching on/off large electric motors and in
circuit breaker switches which replace fuses. The low
current in one circuit with an electromagnet like the
ignition circuit in a car causes the coil to become
magnetic and attract the soft iron armature thus closing
the contact C in the diagram thus switching on the
other circuit in a large current is needed, like a car
starter motor. A heavy duty circuit directly to the
ignition switch in a car could cause dangerous
sparking.
Electromagnetic Relay circuit
Switch
Soft iron
armature
Coil
Heavy duty
circuit
M
Current in a Magnetic field
The force experienced by a current in a magnetic field is the principle on which the electric motor, moving coil
loudspeaker, moving coil galvanometer, ammeter, voltmeter and multimeter is based on.
Moving Coil Loudspeaker: coil between poles of a permanent magnet attached to a movable diaphragm. When
I flows the coil experiences a force moving the diaphragm.
Meters: Moving coil galvanometer two opposing torque's, one due I in a magnetic field (TI) and one due to the
tension on the spring (Tr). When they are equal the needle stops. Since T r   and TI  I therefore   I. Very
sensitive, can measure very small currents. Moving coil ammeter: made by placing a resistor(shunt) in parallel
with a moving coil galvanometer. To find R remember the p.d. across both R and G are the same. i.e. V shunt =
Vgal. therefore IsRs=Ig Rg. Moving coil voltmeter: made by placing a galvanometer in series with a resistor
(multiplier). To find Rm the total voltage Vt=VR + Vg Ohmmeter: made by placing a galvanometer in series with
a resistor and a cell. f.s.d. = zero resistance. The scale is not linear. The resistor is chosen so that when no
resistance to be measured is connected the current flowing gives a f.s.d. A multimeter a device that is all three
meters in one unit.
Generators are the reverse of electric motors, convert Ek into electrical energy. The A.C. generator consists of
slip rings, carbon brushes, coil, and permanent magnets. The output varies sinusoidally hence A.C.
Induction Coil: Made of a thick wired primary coil with few turns, and a thin wired secondary coil with many
turns, on top of the primary, with a soft iron core. It is a device for producing a large voltage from a low d.c.
voltage. How it works: when the current is switched on it builds up slowly inducing a small e.m.f. in the
secondary, when the current is switched off it falls very rapidly implying a rapidly changing magnetic field
inducing a very large e.m.f. in the secondary. A make/ break circuit with contact breaker points achieves the
on/off. Practical use = ignition system of a car.
Back e.m.f. Turning a coil induces an e.m.f., so when a motor is turning it produces another e.m.f. which opposes
the due the motor action, hence back e.m.f. This means that the current in a running motor is less than is starting,
to protect the coil a variable resistance is put in series with it.
Induction Motor: when a magnet moves the disc is in a changing magnetic field. so a current is induced in it the
flow of which causes magnetic fields opposing the motion of the magnet. (Lenz's law). Since the magnet cannot
move backwards the disc moves forwards. In a practical induction motor two electromagnets at right angles with
a capacitor in series with one (to make it 90o out of phase) to the disc.
Light emitting diode (l.e.d.): some semi-conductor materials when they are forward bias and the electrons an
holes combine, the electrons lose their energy as light rather than heat. Made of gallium arsenide phosphide.
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Used in calculators, clock displays, indicator lights, transmitting information along optical fibres. They are more
reliable, faster, smaller and use less current than filament bulbs.
Photodiodes: A reverse bias diode, very small current, due to few charge carriers. As temperature goes up, more
charge carriers for conduction, so the greater the light intensity the greater the current. Used in photometers,
high-speed counters, alarm systems and at the receiving end of optical fibres.
Bipolar
Transistor
c
nb
pne
Transistors
Bipolar transistor: npn, consists of emitter (e), very thin base (b) and collector (c). I b  Ic (in
fact 100- 1000 times Ib), often referred to as a current amplifier. The base is positive w.r.t. to the
emitter, forward bias, but the base is so thin that 99% of the electrons pass through to the
collector (reverse bias) to form Ic attracted by the positive terminal of the battery., very few
electrons combine with holes in the base. Ic is independent of the voltage for voltages above
0.6V (for Si). Ic depends on Ib so the transistor can also act as current switch. Ie=Ib+Ic
Transistor as a switch
6V
TH3
22k
R I splits here
Transistor as a switch: Referring to the circuit . when the thermsistor
is cold it has a large resistance, therefore a small current. so there is a
very little current in the base (a small fraction), the transistor is off as
the base current is too small. When the thermistor is warm the opposite
is the case and the light is switched on. Uses include fire alarm, switch
On/off Street light, and burglar alarm. If the collector current is not
large enough then a magnetic relay may be used. Note R provides an
alternative pathway for the current, so if its value too large the transistor
will always be on, and if it is too small the transistor is always off.
0V
Transistor as a current amplifier: Remember a small change in Ib
gives a large change in Ic . For example amplifying the signal from an aerial or a microphone. A battery in the
base circuit ensures the transistor is always on. In practice more than one transistor is needed.
Transistor as a voltage inverter (NOT gate): If the base A is
speaker
connected to the 6V line means a base current will flow,
Microphone
transistor on and a large p.d. across R then Vo is low ( i.e. 0) If
A is connected to the 0V line then no base , and current
transistor is off, Vo is high ( i.e. 1).
Transistor as a voltage amplifier: The same type a circuit is
used as for the current amplifier except with a load resistor in the
Transistor as a I amplifier
collector circuit. Vi low gives Vo high and vice versa. Small
changes in the input give large changes in the output voltage. See circuit on the next page.
10 k
6V
1.2k load
resistor
22k
Vi
Logic gates: Circuits used in calculators, computers etc. depend on
logic gates. Vo (output) depends on Vi (input), low Vo=0 and high
Vo=1.
V0
0V
Voltage amplifier
Integrated circuits: A complete circuit with transistors, diodes,
resistors and capacitors made into a single Si chip, more than a
million components possible.
AND GATE: Both diodes A and b connected to the 6V line then no
current flows through the resistor therefore Vo= 6V (high). If A or
B, or A and B are connected to the 0V line then one or both diodes
are forward bias and a current flows in the resistor Vo= 0V (low)
OR GATE: If A or B or A and B are connected to the 6V line one or
both diodes are forward bias, Vo=6V (high). If A and B are connected to the 0V line Vo= 0V (low).
Exp. To establish truth tables for AND and OR gates.
Set up circuits as shown in the diagrams. Connect the diodes in turn to the 0V lines and 6V lines. Record the
input and output voltages as high (1) or low (0)
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A
1
1
0
D.M.A ©
AND Gate Truth Table
B
1
0
1
Vo
1
0
0
OR Gate Truth Table
B
1
0
1
A
1
1
0
Vo
1
1
1
6V
A
NOT Gate
V0
0V
0
AND Gate
0
0

k
0
+6V
0
0
+6V
Vo
0V
Vo
OR Gate
k

0V
Exp. To Establish a truth table for a NOT gate
Set up a circuit as show opposite, record the input and output voltages when A is connected to the 0V and 6V
line.
Truth table for a NOT gate
A
V output
1
0
0
1
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