Download Physics Booklet for Form 3

This booklet contains notes for guidance,
intended for students who will sit for the
Form III National Assessment in Physics. It
is a free booklet meant to help Mauritian
students in Physics and it is not for sale.
Physics
National Assessment 2017
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Dushan BOODHENA
Table of Contents
CHAPTER ONE: MEASUREMENT .................................................................................................... 4
Measurement of length ...................................................................................................................... 4
Common types of errors and their prevention ................................................................................... 4
End error ......................................................................................................................................... 4
Zero error ........................................................................................................................................ 4
Parallax error................................................................................................................................... 5
How to read a Vernier scale? .............................................................................................................. 5
Measurement of volume .................................................................................................................... 7
Volumes of liquids ........................................................................................................................... 8
Measurement of time ......................................................................................................................... 9
Measurement of mass ........................................................................................................................ 9
Measurement of temperature ............................................................................................................ 9
CHAPTER TWO: MOTION ............................................................................................................ 11
Scalar and vector quantities ............................................................................................................. 11
Linear motion (Optional)................................................................................................................... 11
Distance and displacement ............................................................................................................... 11
Speed and velocity ............................................................................................................................ 12
Average speed and average velocity (Optional) ............................................................................... 13
Acceleration ...................................................................................................................................... 13
Distance-time (s-t) graphs (Optional) ............................................................................................... 14
Speed-time (v-t) graphs .................................................................................................................... 15
CHAPTER THREE: ENERGY ........................................................................................................... 19
The SI unit of energy ......................................................................................................................... 19
The various forms of energy ............................................................................................................. 19
Renewable and non-renewable sources of energy (Optional) ......................................................... 19
The need for alternative energy sources (Optional) ......................................................................... 19
Advantages and disadvantages of different energy sources (Optional) ........................................... 20
Biomass ......................................................................................................................................... 20
Hydroelectric energy ..................................................................................................................... 20
Solar energy .................................................................................................................................. 20
Tidal energy................................................................................................................................... 20
Wind energy .................................................................................................................................. 20
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Chemical energy (fossil fuels) ....................................................................................................... 20
Nuclear energy .............................................................................................................................. 20
Work done ........................................................................................................................................ 20
Kinetic energy ................................................................................................................................... 21
Potential energy ................................................................................................................................ 21
The law of conservation of energy.................................................................................................... 21
Power ................................................................................................................................................ 22
Ways and means to save energy (Optional) ..................................................................................... 23
To save electrical energy ............................................................................................................... 23
To save fuel energy ....................................................................................................................... 23
CHAPTER FOUR: OPTICS ............................................................................................................. 25
Light travels in straight lines ............................................................................................................. 25
Luminous and non-luminous bodies ................................................................................................. 25
The laws of reflection........................................................................................................................ 25
Common applications of reflection of light ...................................................................................... 26
Lateral inversion............................................................................................................................ 26
Rear-view mirror and blind spot ................................................................................................... 27
The periscope ................................................................................................................................ 27
Ray diagram for a point object reflected in a mirror ........................................................................ 28
Refraction of light ............................................................................................................................. 29
Laws of refraction ......................................................................................................................... 29
Common applications of refraction of light ...................................................................................... 30
Real depth and apparent depth .................................................................................................... 30
Lenses............................................................................................................................................ 30
CHAPTER FIVE: ELECTRICITY........................................................................................................ 33
Electrical charge and electric current ............................................................................................... 33
Conductors and Insulators ................................................................................................................ 33
Current .............................................................................................................................................. 33
Potential difference .......................................................................................................................... 34
Electrical resistance and Ohm’s law.................................................................................................. 34
Experiment to determine the resistance of a metallic conductor .................................................... 35
Resistors in series.............................................................................................................................. 36
Resistors in parallel ........................................................................................................................... 37
Direct current (D.C) circuits .............................................................................................................. 39
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Safe use of electrical energy (Optional) ............................................................................................ 40
Saving electrical energy (Optional) ................................................................................................... 40
INDEX………………………………………………………………………………………………………………………………………….42
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CHAPTER ONE: MEASUREMENT
Physics is the science of matter, motion and energy. Whichever branch of science we study, we have
to make accurate measurements to ensure standard and universally accepted values.
During the measurement of simple quantities, we:
1. ask different persons to repeat the measurement (sometimes with a different set of the
same instrument) to ensure that the values are the same or, at least, very close to each
other,
2. repeat the measurement at least four times and then calculate the average value,
3. express the physical quantity as a number, a unit and sometimes a direction, for example,
‘10 m to the North.’
Measurement of length
Experiment 1: To measure the length and width of the Physics laboratory using a measuring tape.
Experiment 2: To measure the length and width of a book using a metre-rule.
Experiment 3: To measure the inside and outside diameters of a boiling tube using Vernier callipers.
Length is the distance between two points and is measured in metres (m). Longer distances like
javelin or discus throws are measured using measuring tapes. Average distances, like the length of a
book, are measured with a metre rule, half-metre rule or ruler. Shorter distances, like the diameter
of a coin, are measured with Vernier callipers (also written as ‘calipers’).
Common types of errors and their prevention
End error
An end error arises with metre rules and half-metre rules. This occurs because the zero marks of
these instruments are situated at their very ends. When the ends of these rules wear out with time,
their zero marks are no longer available.
To overcome an end error, we start with the 1 cm mark and then subtract the 1 cm from the scale
reading in order to get the correct length of the object.
Notice that in an ordinary ruler, there is a gap or dead space before the zero mark. The problem of
end error cannot therefore arise with an ordinary ruler although we may have a zero error if we
measure from its end. Measured values will be smaller than the true value.
Zero error
Theoretically, when we close the jaws of a Vernier calliper completely, we should get a reading of
0.00 cm because we are not measuring any length. In practice, however, some Vernier callipers will
still give a small reading when they are completely closed. We say that there is a zero error on this
instrument.
To overcome any zero error arising from a Vernier calliper, we subtract the zero error from the
measured length, in order to get the true length.
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Parallax error
Metre rules and half-metre rules are thick. Because of this thickness, if we do not place one eye
perpendicular to its scale, we will read a value which is too high or too low. We say that parallax
error has occurred.
To overcome parallax error we should read with only one eye placed directly above the scale.
How to read a Vernier scale?
Step 1: Where is the zero of the Vernier pointing on the main scale? If it points between two
numbers (3.0 and 3.1 in the example below), always choose the smaller number as the main
scale reading.
Step 2: Number the Vernier scale readings as 0, 5 and 10. Which line on the Vernier scale is matching
exactly with any line on the main scale? This is the Vernier scale reading which gives the
second decimal place.
Step 3: Add the main scale reading in step 1 to the Vernier scale reading in step 2.
3.0
2
0
3.1
4
45
10
3.0 4 cm
Vernier reading=
measured length = main scale reading + Vernier scale reading
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Details of the commonly used instruments are given below:
Instrument
Usual Range
Measuring tape
0—100 m
Metre rule
Smallest
Division
1 cm
0—1 m
0.1 cm
or 1 mm
Half-metre rule
0—50 cm
0.1 cm
or 1 mm
Vernier callipers
0—12.5 cm
0.01 cm
or 0.1 mm
Uses
Special Precautions
 Place eye directly
above scale (to avoid
parallax error).
 Avoid using the 0
mm mark to avoid
end error.
To measure the
 Place eye directly
length and width
above scale.
of a table
 Avoid using the 0
mm mark.
To measure the
 Place eye directly
length and width
above scale.
of a book
 Avoid using the 0
mm mark.
To measure the
 Unlock the locking
diameter of a coin
screw while
or the
measuring.
inside/outside
 Subtract any zero
diameter of a
error on the
pipe
instrument.
To measure
Javelin or discus
throws

Some useful conversions of length are:
1 km = 1000 m
1 m = 100 cm
1 cm = 10 mm
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Measurement of volume
Volume is the space occupied by an object in three dimensions and it is measured in cubic metres
(m3) or cubic centimetres (cm3). For regular objects, we use appropriate formulae to calculate their
volumes.
SHAPE
FORMULA TO CALCULATE ITS VOLUME
Cube
Length, l
Volume = length x length x length
V =
l3
Cuboid
height, h
breadth, b
Volume = length x breadth x height
V = l
x
b
x h
length, l
Sphere
𝟒
radius, r
Volume = 𝟑 x π x radius x radius x radius
V
=
𝟒
𝟑
π r3
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Experiment 4: To determine the volume of a stone using the displacement method.
To measure the volume of an irregular solid such as a stone, we use the displacement method
described below:
thread
measuring cylinder
final volume
initial volume
A measuring cylinder is filled with a known volume of water. Using a thread, the stone whose
volume is to be determined is carefully immersed into the measuring cylinder. The final volume is
then noted. The volume of the irregular object is given by the formula:
volume of irregular object = (final volume—initial volume)
Precautions:
1. The measuring cylinder must be placed on a flat, horizontal surface, free from mechanical
vibrations.
2. The readings should be taken by placing one eye on the same level as the liquid meniscus.
3. A very thin thread should be used to immerse the irregular solid.
4. The solid should not dissolve in the liquid, nor should there be air bubbles on the surface of
the solid.
Before reading the volume, we must place the eye on the same level as the lowest part of the
meniscus.
Volumes of liquids
The volume of a liquid is measured directly by placing it in a measuring cylinder.
If the liquid is mercury, we must place one eye on the same level as the top of the meniscus before
taking the reading.
For all other liquids, we must place one eye on the same level as the bottom of the meniscus before
taking the reading.
Some useful conversions of volume are:
1 m3 = 1,000,000 cm3 or ml
1 cm3 = 1000 mm3
1 litre or l = 100 cl = 1000 ml or cm3
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Measurement of time
Experiment 5: To measure the time it takes for a feather to fall to the ground using a stopwatch
(both analogue and digital).
Time is a measure of the duration of an event and it is measured in seconds (s). Long intervals of
time are measured using a clock. Shorter intervals of time are measured using an analogue or digital
stopwatch. Analogue stopwatches may have a zero error on them which need to be subtracted.
Some useful conversions of time are as follows:
1 day = 24 h
1 h = 60 minutes
1 minute = 60 seconds
Measurement of mass
Experiment 6: To measure the mass of a stone.
The mass of an object tells us how much matter it contains and it is measured in kilograms (kg). It
can be measured using an electronic balance or a beam balance. An electronic balance reads and
displays the mass of an object directly but it must be placed on a flat horizontal surface free from
mechanical vibrations. A beam balance uses a set of standard masses to compare the mass of the
object.
Some useful conversions of mass are as follows:
1 kg = 1000 g
1 g = 1000 mg
Measurement of temperature
Experiment 7: To measure the room temperature with a laboratory thermometer.
Temperature is the degree of hotness and it is measured in degrees celsius (0C) with a thermometer.
The S.I unit of temperature is the kelvin (K). We add 273 to a temperature in 0C to convert it into a
temperature in K.
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worn out ends of
metre and half-metre
rules
K = 0C + 273
start with another
mark and subtract its
value
Measured in kelvins
(K)
wrong position of eye
when measuring
value of zero error
determined with
nothing measured
defect or feature in
instrument
1 m = 100 cm
place eye
perpendicular to
scale before
measuring
subtract zero error
from instrument
occurs because of
occurs because of
1 km = 1000 m
1 cm = 10 mm
occurs because of
solution
solution
Range: 0 to 100 m
solution
End error
Zero error
measured with
Parallax error
Meaured with a
laboratory
thermometer
Meaured in metres
(m)
accuracy
Measurement of
temperature
1 day = 24 h
1 h = 60 minutes
Measuring tape
unit
Smallest division
reads 1 cm
To measure distance
for javelin or discus
throws
where used?
Longer distances
Common types of
errors
Measured in seconds
(s)
Metre rule
Measurement of
length
1 minute = 60 s
measured with
Range: 0 to 1 m
unit
Average distances
Measurement of
time
Long intervals
measured with a
clock
accuracy
Measurement
where used?
To measure length
and width of a table
Shorter intervals
measured with an
analogue/digital
stopwatch
Shorter distances
measured with
Measurement of
volume
Subtract any zero
error for an analogue
stopwatch
Measured in
kilograms (kg)
Measurement of
mass
unit
1 kg = 1000 g
Measured with an
electronic balance
Volume of irregular
solid = (final volume initial volume)
calculation
Place on a flat,
horizontal surface,
free from vibrations
Place measuring
cylinder on a flat,
horizontal surface
Read at the bottom
of meniscus
Range: 0 to 12.5 cm
Smallest division
reads 0.1 mm
To measure inside/
outside diameters of
a test-tube
For liquids, use a
measuring cylinder
Place eye on same
horizontal level as
liquid
for most liquids
precaution
Vernier callipers
where used?
unit
For irregular solids
use the displacement
method
Place eye at same
horizontal level as
liquid
Standard masses
have to be used for
comparison
accuracy
Measured in cubic
metres m3
Compared on a beam
balance
1 g = 1000 mg
Smallest division
reads 1 mm
Read at the bottom
of meniscus for most
liquids
Read at the top of
meniscus for mercury
For regular objects
use formuale
1 m3 = 1,000,000 cm3
or ml
Volume of cube =
length x length x
length
1 cm3 = 1000 mm3
Volume of cuboid =
length x breadth x
height
Volume of sphere =
4/3 x π x radius x
radius x radius
1 litre or l = 100 cl =
1000 ml or cm3
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CHAPTER TWO: MOTION
Scalar and vector quantities
A scalar quantity is one which has magnitude or size only, but no direction. Examples of scalar
quantities are mass, length, time, distance, speed, etc. When scalar quantities are added, we simply
add their magnitudes.
A vector quantity is one which has both magnitude and direction. Examples of vector quantities are
displacement, velocity, acceleration, force, etc. When vector quantities are added, we have to
consider both their magnitudes and their directions.
Worked Example:
Calculate the resultant force in the following:
(a)
2N
5N
Resultant force = 5 + 2 = 7 N to the right←
(b)
5N
2N
Resultant force = 5—2 = 3 N to the right←
Linear motion
Linear motion refers to motion in a straight line. When considering linear, unidirectional motion we
may use the terms distance and displacement interchangeably. We may also interchange the terms
speed and velocity when we talk about linear, unidirectional motion.
When the direction of the moving object changes, then distance and displacement are two different
things. We say that the object is undergoing non-linear motion. The speed and velocity of a moving
object will have different values in non-linear motion.
Distance and displacement
Distance is the length of the path between two points, regardless of the direction.
Displacement is the distance and direction between two points.
Both distance and displacement are measured in metres (m).
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Distance is classified as a scalar quantity because it has magnitude or size only but no direction. For
example, when we say that the driving distance between town A and town B is 5000 m, this means
that the distance by road between these two points is 5000 m. It is not necessarily the distance
measured in a straight line!
Displacement on the other hand, is classified as a vector quantity because it has both magnitude and
direction. For example, when we say that the displacement of town B from town A is 3000 m due
North, this means that if we draw a straight, imaginary line pointing North from town A, we will find
town B 3000 m away along this same line.
Speed and velocity
The speed of a body is its distance travelled per unit time.
It is a scalar quantity. When stating a speed we must state its magnitude and its unit.
𝐬𝐩𝐞𝐞𝐝, 𝐢𝐧 𝐦/𝐬 =
𝐝𝐢𝐬𝐭𝐚𝐧𝐜𝐞 𝐭𝐫𝐚𝐯𝐞𝐥𝐥𝐞𝐝, 𝐢𝐧 𝐦
𝐭𝐢𝐦𝐞 𝐭𝐚𝐤𝐞𝐧, 𝐢𝐧 𝐬
The velocity of a body is its displacement per unit time. We can also define velocity as the distance
travelled per unit time in a specified direction.
It is a vector quantity. When stating a velocity, we must state its magnitude, its unit and its direction.
𝐯=
𝐬
𝐭
where, v = velocity, in m/s,
s = displacement, in m,
t = time taken, in s
Both speed and velocity are measured in metres per second (m/s or m s-1).
If the direction of a moving object is changing, its speed may be constant but since its direction is
changing its velocity will not remain the same.
Worked example:
N
B
5000 m
3000 m
A
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The distance by road from town A to town B is 5000 m. B is situated 3000 m to the North of A. If a
car takes 1000 s to travel from town A to town B by road, calculate:
(a) its speed,
distance travelled 5000
speed =
=
= 5 m/s ←
time taken
1000
(b) its velocity
s 3000
velocity, v = =
= 3 m/s due North ←
t 1000
Note: We can also state the velocity as ‘3 m/s along AB’.
Average speed and average velocity
An object does not always move at a constant speed or constant velocity all the time. At times it
stops, at other times it moves with different speeds. For example, a car may have to stop at the
traffic lights but the driver can catch up by moving faster!
The speed or velocity of a body at a precise instant is called its instantaneous speed or instantaneous
velocity. For a car the instantaneous speed can be read on its ‘speedometer’. For the whole trip or
journey of a moving object, we prefer to use the terms ‘average speed’ or ‘average velocity.’
Average speed is the ratio of the total distance travelled to the total time taken:
𝐚𝐯𝐞𝐫𝐚𝐠𝐞 𝐬𝐩𝐞𝐞𝐝 𝐢𝐧 𝐦/𝐬 =
𝐭𝐨𝐭𝐚𝐥 𝐝𝐢𝐬𝐭𝐚𝐧𝐜𝐞 𝐭𝐫𝐚𝐯𝐞𝐥𝐥𝐞𝐝, 𝐢𝐧 𝐦
𝐭𝐨𝐭𝐚𝐥 𝐭𝐢𝐦𝐞 𝐭𝐚𝐤𝐞𝐧, 𝐢𝐧 𝐬
Average velocity is the ratio of the total displacement to the total time taken:
𝐚𝐯𝐞𝐫𝐚𝐠𝐞 𝐯𝐞𝐥𝐨𝐜𝐢𝐭𝐲 =
𝐭𝐨𝐭𝐚𝐥 𝐝𝐢𝐬𝐩𝐥𝐚𝐜𝐞𝐦𝐞𝐧𝐭
𝐭𝐨𝐭𝐚𝐥 𝐭𝐢𝐦𝐞 𝐭𝐚𝐤𝐞𝐧
For an object which is undergoing uniform acceleration:
𝐮+𝐯
< 𝐯 >=
𝟐
where <v> = average velocity, in m/s,
u = initial velocity, in m/s,
v = final velocity, in m/s
Acceleration
Acceleration is the rate of change of velocity per unit time.
Acceleration is measured in metres per second per second, simply written as m/s2 or m s-2.
𝐯−𝐮
𝐚=
𝐭
where, a=acceleration, in m/s2 or m s-2,
u=initial velocity, in m/s,
v=final velocity, in m/s,
t=time taken, in s
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Acceleration gives us an idea of how fast a moving object is changing its velocity with time. For
example, if an object is dropped on Earth, its downward velocity will increase by about 10 m/s after
each second. We say that the acceleration due to gravity (also known as the acceleration of free fall)
is about 10 m/s per s, or simply 10 m/s2, directed vertically downwards.
A positive value of acceleration means that the object is speeding up: we say that the object is
undergoing acceleration. A negative value of acceleration means that the object is slowing down: we
say that the object is undergoing retardation.
Distance-time (s-t) graphs (Optional)
A distance-time graph is a graph of distance (y-axis) against time (x-axis). It tells us the position of an
object at different times during its journey.
For linear, unidirectional motion, the gradient of a distance time graph gives the speed of the object:
𝐬𝐩𝐞𝐞𝐝 = 𝐠𝐫𝐚𝐝𝐢𝐞𝐧𝐭 𝐨𝐟 𝐝𝐢𝐬𝐭𝐚𝐧𝐜𝐞 − 𝐭𝐢𝐦𝐞 𝐠𝐫𝐚𝐩𝐡 =
𝐫𝐢𝐬𝐞
𝐫𝐮𝐧
Below is the graph of an object which is not moving. The object is said to be ‘at rest’ and the graph is
a horizontal line placed at any height above, below or even on the x-axis:
s/m
t/s
The graph shown below is obtained for an object moving with uniform or constant speed. Its
gradient is the same anywhere along the line:
s/m
t/s

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Worked Example:
Below is a distance-time graph for a person in a room.
distance in m
2
1.5
1
0.5
rise
0
1
run
2
3
4
5
6
7
8
9
time in s
Describe her journey.
She walks for 2 seconds and then stops for 2 more seconds. She then walks faster for one second
before stopping for a further 4 seconds.
Calculate her initial speed.
initial speed = gradient of graph =
rise 0.5
=
= 0.25 m/s ←
run
2
Speed-time (v-t) graphs
A speed-time graph is a graph of speed (y-axis) against time (x-axis). For an object which is
undergoing linear, unidirectional motion, the gradient of its speed-time graph gives its acceleration.
acceleration, in m/𝐬𝟐 = gradient=
rise
run
For an object which is undergoing linear, unidirectional motion, the area under its speed-time graph
gives its distance travelled.
area under v-t graph=displacement, in m
Below is the graph for an object at rest. Both its speed and its acceleration are zero:
v/ms-1
t/s
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The graph shown below is obtained for an object moving with uniform or constant speed. There is
no change in speed and so its acceleration is zero:
v/ms-1
t/s
Below is the graph for an object moving with uniform or constant acceleration. After each second, a
constant speed is being added to its previous speed:
v/ms-1
t/s
The graph shown below is for an object moving with uniform or constant deceleration or
retardation. After each second, a constant speed is being subtracted from its previous speed:
v/ms-1
t/s
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Worked Example:
A car starts from rest and accelerates uniformly for 5 s and reaches a speed of 20 m s-1. It continues
to move with this speed for 10 s till it comes to rest with uniform deceleration for a further 5 s.
(a) Sketch a speed-time graph to illustrate the motion of the car.
speed in m/s
30
20
rise
(negative)
10
0
5
10
15
run
20
time in s
(b) Calculate the deceleration of the car.
rise −20
Acceleration = gradient =
=
= −4
run
5
∴Deceleration = 4 m/s2←
(c) What is the total distance travelled by the car?
Total distance travelled=area under v-t graph (trapezium)
1
2
1
(10 +
2
= (sum of parallel sides)x(perpendicular distance between them)
=
20) x 20
= 300 m← (not m2 !!!)
(d) Calculate the average speed of the entire journey.
total distance travelled 300
Average speed =
=
= 15 m/s ←
total time taken
20
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Length of path
between two points,
regardless of
direction
Scalar quantity
Measured in metres
(m), e.g 22 m
definition
has magnitude or size
only
has both magnitude
and direction
Distance and
direction between
two points
unit
Vector quantity
measured in (m), e.g
22 m to the North
definition
unit
Distance
Displacement
Scalar quantity
Measured in m/s, e.g
65 m/s upwards
Vector quantity
Measured in m/s, e.g
65 m/s
unit
Scalar quantity
average speed 
total dis tan ce travelled
vector quantity
unit
formula
Motion
Speed
Velocity
formula
average velocity 
total time
formula
total time taken
formula
definition
speed 
total displacement
dis tance travelled definition
velocity 
displacement
time taken
time taken
Speed-time graph
Distance-time
graph
distance travelled per
unit time
Acceleration
formula
definition
formula
speed=gradient
rise

run
Graph of distance (yaxis) against time (xaxis)
displacement per unit
time
Rate of change of
velocity per unit time
v u
a
t
unit
Measured in m/s2, e.g
acceleration due to
gravity=10m/s2
vertically downwards
Vector quantity
formula
formula
displacement=area
under v-t graph
Graph of speed (yaxis) against time (xaxis)
acceleration=gradient
rise

run
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CHAPTER THREE: ENERGY
The SI unit of energy
Energy is the capacity to do work. It is measured in a unit called joule (J). In Physics, work is said to
be done when an object is made to move or when a moving object is stopped.
The various forms of energy
The commonly known forms of energy are mechanical energy, heat, light, sound, electrical energy,
chemical energy or nuclear energy. But all forms of energy can be classified into two broad types
namely potential energy or kinetic energy.
Energy can change from one form to another during a process. For example, hydroelectric
generation, which is the generation of electrical energy from flowing water, involves interchanges of
various forms of energy.
We can represent this change using a flow diagram as shown below:
Potential
energy of
water
At the top
of a dam
Kinetic
energy of
water
At bottom
of the dam
Electrical
energy
From
generator
Renewable and non-renewable sources of energy
Some energy sources like biomass, hydroelectric energy, solar energy, tidal energy, wind energy are
called renewable energy or alternative energy sources. They refer to usable energy derived from
replenishable sources.
Fossil and nuclear fuels are, on the other hand, non-renewable or finite energy sources. One day
they will be completely used up.
The need for alternative energy sources
Fossil fuels include coal, petroleum, natural gas and heavy oils. They will all be used up in less than
two centuries.
Burning fossil fuels can also cause air pollution and lead to global warming by the emission of
greenhouse gases like carbon dioxide. Global warming refers to the measurable increases in the
average temperature of the Earth’s atmosphere, oceans and landmasses. Gases like carbon dioxide,
methane or nitrogen dioxide can trap too much of the Sun’s heat and cause global warming. Carbon
dioxide and nitrogen dioxide come from the burning of fossil fuels like petroleum, coal and natural
gas (methane).
Global warming will cause a rise in the sea level. It will also be responsible for destructive climatic
conditions. This will eventually cause the extinction of many plant and animal species.
This is why there is a need for alternative energy sources for the future of humankind.
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Advantages and disadvantages of different energy sources
Biomass
The term biomass refers to plant materials and animal waste used especially as a source of fuel.
Biomass energy is derived from five distinct energy sources: garbage, wood, waste, landfill gases,
and alcohol fuels. They are renewable sources of energy but are thought to contribute to global
warming by the emission of carbon dioxide gas.
Hydroelectric energy
It refers to electricity produced from generators driven by water turbines that convert the potential
energy of falling or fast-flowing water to mechanical energy. Although the electricity produced is
cheap, it costs a lot to build such power stations.
Solar energy
Solar energy refers to radiation from the Sun capable of producing heat, causing chemical reactions,
or generating electricity. Although it is a cheap source of energy and does not cause pollution, it is
available only during the day.
Tidal energy
Tidal energy refers to any form of renewable energy in which tidal action in the oceans is converted
to electrical energy. Although it is cheap it costs a lot to build them. But it can disrupt estuarine
ecosystems during their construction and operation.
Wind energy
Wind energy is a form of energy conversion in which turbines convert the kinetic energy of wind into
mechanical or electrical energy. Although it is cheap, it is only available intermittently.
Chemical energy (fossil fuels)
Chemical energy is easy to obtain simply by burning fossil fuels but they cause pollution and lead to
global warming. Fossil fuels are also non-renewable sources of energy.
Nuclear energy
Nuclear energy, also called atomic energy refers to energy that is released in significant amounts in
processes that affect atomic nuclei, the dense cores of atoms. Large amounts of energy are
produced from small amounts of nuclear fuels but the danger of nuclear accidents is ever present.
Nuclear fuels are also non-renewable sources of energy.
Work done
Work is said to be done when a force produces movement. Work done is a measure of the energy
that we need to move an object or to stop a moving object and, like all other forms of energy, it is
also measured in joules.
𝐖=𝐅𝐬
where, W = work done , in J,
F = force, in N,
s = displacement in direction of force, in m
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Worked Example:
What is the amount of energy required to push an object horizontally over a distance of 100 m with
a force of 40 N?
Energy required = work done, W = F s = 40 x 100 = 4000 J or 4 kJ ←
Kinetic energy
The kinetic energy is the energy that a body has because it is moving.
EK =
1
m v2
2
where EK = kinetic energy, in J,
m = mass of the body, in kg,
v = final velocity of the body, in m/s
Thus, wind energy is itself a form of kinetic energy.
Worked example:
Calculate the kinetic energy possessed by a shooting star of mass 0.001 kg moving at a speed of 100
m/s.
1
1
Kinetic energy, EK = mv 2 = x 0.001 x (100 x 100) = 5 J ←
2
2
Potential energy
The potential energy is the energy that a body has because of its position or state.
𝐄𝐏 = 𝐦 𝐠 𝐡
where EP = gravitational potential energy, in J,
m = mass of the body, in kg,
g = gravitational field strength=10 N kg-1,
h = height above a reference level, in m
Thus, chemical or fuel energy is a form of potential energy as it involves the regrouping of atoms.
Nuclear energy is also potential energy at the subatomic level.
A spring or elastic band also has ‘elastic potential energy’ when wound or stretched.
Worked example:
A climber ascends a mountain top of height 1200 m. If the climber has a mass of 60 kg, deduce
(a) the gravitational potential energy he acquires,
Gravitational potential energy, EP = m g h = 60 x 10 x 1200 = 720 000 J or 720 kJ ←
(b) where this energy comes from.
From the chemical energy stored in his body as food.
The law of conservation of energy
Energy can neither be created nor destroyed in any process. It can be converted from one form into
another or transferred from one body to another, but the total amount remains constant.
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Worked Example:
A ball of mass 12 kg is released from a height of 10 m above the ground (position A).
A
B
10 m
C
(a) What type of energy does the ball have at B?
Both potential and kinetic energies.
(b) Calculate the velocity with which the ball hits the ground at C.
Neglecting energy losses,
EP of ball at A=EK of ball at C
1
mgh= mv 2
2
2
v =2gh
velocity with which ball hits the ground, v=√2gh=√2x10x10=14 ms-1
(c) Suggest why the velocity you have calculated in (b) is usually different from its actual value,
and state the energy changes that take place.
Most of the potential energy of the ball is converted into kinetic energy, while some energy
is lost, mainly as heat, in overcoming frictional forces.
Power
Power is the rate of doing work or energy converted.
𝐏=
𝐖 𝐄
𝐨𝐫
𝐭
𝐭
where P = power, in joules per second (J s-1) or in watts (W),
W = work done, in J,
E = energy converted, in J,
t = time taken, in s
Thus, an electric bulb having a power of 60 W means that each second the bulb converts 60 J of
electrical energy into heat and light.
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Worked example:
A car is moved through a horizontal distance of 25 m by a force of 800 N in 4 s. Calculate the power
developed in doing so.
W F s 800 x 25
Power developed, P = =
=
= 5000 W or 5 kW ←
t
t
4
Ways and means to save energy
We need to save energy so that our non-renewable resources can last longer on the planet and also
to combat the problem of climate change which is a consequence of global warming.
To save electrical energy
1. Replace electrical heaters by solar heaters.
2. During the day, replace electrical lighting by natural lighting, by opening all window and door
curtains. Use energy-efficient light bulbs and fluorescent tubes rather than using filament
bulbs.
3. Use energy-efficient refrigerators and other electrical appliances.
4. Turn off unnecessary lighting and appliances as soon as they are no longer needed.
To save fuel energy
1. Drive slowly since driving fast burns more fuel for the same distance covered.
2. Keep your car well cleaned and your tyres well inflated to reduce fuel wastage.
3. Use public transport rather than cars. (For a particular journey, one bus will burn much less
fuel for 60 passengers, compared to the amount of fuel that would be burnt if each of the 60
passengers was travelling in his private car).
4. Promote alternative forms of transport like the bicycle.
5. Go to a place on foot whenever you can.
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Replace electrical
heaters by solar
heaters
Replace electrical
lighting by natural
lighting
Use energy efficient
electrical appliances
Work is done when a
force produces
movement
light
W Fs
sound
heat
mechanical
Turn off unnecessary
lighting or appliances
electrical
chemical
Promote alternative
forms of transport
Measured in joules (J)
Can neither be
created nor
destroyed
formula
definition of work done
nuclear
Use public transport
conservation of energy
Can be broadly
classified as potential
energy or kinetic
energy
unit
Forms of energy
Plant materials and
animal wastes used
as fuel
Capacity to do
work
Renewable source of
energy
energy that a body
has because of its
position or state
Saving energy
definition
Biomass
May contribute to
global warming
EP  m g h
formula
Potential energy
Energy
Energy produced by
running water
Electricity produced is
cheap
Hydroelectric energy
energy that a body
has because it is
moving
definition
Kinetic energy
formula
EK 
Costs a lot to build
power station
1
m v2
2
Solar energy
definition
Power
Cheap and clean
source of energy
Nuclear energy
W
t
Measured in watts
(W)
Chemical energy
Energy released from
processes involving
atomic nuclei
Kinetic energy of
winds converted into
electricity
Cheap source of
energy
Costs a lot to build
the power station
P
unit
Wind energy
Cheap source of
energy
formula
Tidal energy
Not available at night
Energy of tidal action
converted into
electricity
rate of doing work or
energy converted
Sources of energy
Energy from radiation
of the Sun
Not available at all
times
Energy obtained by
burning fossil fuels
Easy to obtain
Non-renewable
source of energy
Non-renewable
source of enegy
Causes pollution and
leads to global
warming
Potential nuclear
accident hazard
Large amounts of
energy obtained from
small amounts of
nuclear fuels
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CHAPTER FOUR: OPTICS
Light travels in straight lines
Light is a form of energy which can be detected by the eyes. It is made up of electromagnetic waves
which can travel at a speed of 300,000,000 m/s in a vacuum.
Experiment 8: To show that light travels in a straight line.
light source
cardboard
tiny hole
observer
If the observer is to see the lamp, the holes in the cardboards must all be perfectly aligned. This
shows that light travels in a straight line.
Luminous and non-luminous bodies
A luminous body is one which emits light because it is usually very hot. Examples of luminous bodies
are the Sun, a flame, a lamp or a television screen.
A non-luminous body is one which does not emit visible light, although it may emit infrared or
ultraviolet rays. Non-luminous objects are only visible because they reflect light incident on them.
Examples of non-luminous bodies are the Moon, a table or a cinema screen.
The laws of reflection
A normal is an imaginary line drawn at right angle to the mirror where the incident ray strikes the
mirror.
Experiment 9: To demonstrate the first law of reflection.
The first law of reflection states that the incident ray, the reflected ray and the normal to the
surface, all lie on the same plane.
plane mirror
i
r
incident ray
reflected ray
normal
The angle of incidence is the angle between the incident ray and the normal. The angle of reflection
is the angle between the reflected ray and the normal.
Experiment 10: To demonstrate the second law of reflection.
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The second law of reflection states that the angle of incidence is equal to the angle of reflection, that
is:
𝐢=𝐫
where i= angle of incidence, in degrees,
r=angle of reflection, in degrees.
Worked Example:
A ray of light is incident on the surface of a mirror at an angle of 300, measured from its surface.
(a) What is the angle of incidence?
(b) Hence, deduce the angle of reflection.
normal
i
r
300
(a) Angle of incidence, i = 90 — 30 = 600←
(b) Angle of reflection, r = i = 600←
Common applications of reflection of light
Lateral inversion
Experiment 11: To demonstrate the characteristics of the image formed in a plane mirror.
Some characteristics of the image formed in a plane mirror are:
1. The image is of the same size as the object.
2. The image is virtual, that is, it cannot be formed onto a screen.
3. Image distance from the mirror = object distance from the mirror.
4. The image is upright.
5. The image is laterally inverted (left-to-right inversion).
Because the image formed in a plane mirror is laterally inverted you will see the words POLICE or
AMBULANCE painted on their vehicles as:
ECILOP
and
ECNALUBMA
When these vehicles are behind a driver, the latter can read these two words in his rear-view mirror
as if they were correctly written.
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Rear-view mirror and blind spot
The truck driver can see
cyclist B overtaking but
cannot see cyclist A
A
B
The rear-view mirrors of motor vehicles allow the driver to see what is happening at the back.
However, if a bicycle is overtaking the vehicle too close to it, the driver may not see the cyclist. This
is a potential danger for the latter. This is why rear-view mirrors should be properly adjusted to
enable the driver to see not only what is happening behind, but also what is happening close to the
sides of the vehicle.
The periscope
mirror 1 laterally inverts image
object
image
mirror 2 puts the image right
A periscope is an assembly of two parallel mirrors, both placed at 450, which enables us to look over
high obstacles. Periscopes can be used in submarines to see what is happening at the surface of the
sea, without having to float to the surface. There is no lateral inversion when we look through a
periscope.
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Ray diagram for a point object reflected in a mirror
M
I
O
observer
To show the formation of an image in a plane mirror:
1. Using set-squares, drop a perpendicular from the object through the mirror.
2. Using compasses locate the image I, using the fact that image distance is equal to the object
distance from the mirror.
3. Draw rays of light from the image to the observer’s eye. The lines should be dotted behind
the mirror and continuous in front of it.
4. Draw rays from the object to the mirror and show, using arrows, how it reaches the
observer’s eye.
To the observer, it appears as if the rays are coming from the image.
Worked example:
A man sits in an optical chair, looking into a plane mirror which is 2.5 m away from him, and views
the image of a chart which faces the mirror and is 0.5 m behind his eyes. How far away from his eyes
does the chart appear to be?
chart’s
image
man’s
image
mirror
chart
man
0.5
2.5
2.5
0.5
The chart appears to be 2.5 + 2.5 + 0.5 = 5.5 m from his eyes←
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Refraction of light
Experiment 12: To demonstrate refraction through a glass block.
Refraction is the bending of light as it passes from one transparent material into another. This takes
place because light has different speeds in different optical media.
normal
incident ray
angle of
incidence, i
vacuum/air
optically less dense medium
optically denser medium
glass
angle of
refraction, r
refracted ray
Laws of refraction
The first law of refraction states that the incident ray, the refracted ray and the normal to the
surface, all lie on the same plane.
The angle of incidence is the angle between the incident ray and the normal. The angle of refraction
is the angle between the refracted ray and the normal.
The second law, which is also known as Snell’s law, states that for two optical media, the ratio of the
sine of the angle of incidence to the sine of the angle of refraction is a constant. An optical medium
is a transparent medium through which light can pass.
Snell' s law,
sin i
=constant
sin r
When a ray of light is passing from air to glass or water, it will bend towards the normal. However, if
the same ray of light is passing from glass or water to air, it will bend away from the normal.
Note: The phenomenon of refraction is not observed when the angle of incidence is zero degree.
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Common applications of refraction of light
Real depth and apparent depth
pool appears less
deep to observer
air
water
apparent depth
real depth
bottom of pool
Each year, many people get drowned in swimming pools or in the sea because they have wrongly
estimated the depth of water. This is due to refraction which causes the water to appear less deep
than it actually is. If you want to estimate the depth of water in a pool multiply its apparent depth by
1.5.
Lenses
Experiment 13: to demonstrate the action of a converging and that of a diverging lens.
A lens is a piece of transparent material which is used to converge or diverge rays of light by
refraction, depending on their applications.
A converging lens is thicker in the middle and it will converge a parallel beam of light:
converging lens
Converging lenses are used in telescopes, cameras, photocopying machines and in slide projectors.
There is a converging lens in the human eye too. Converging lenses can also be prescribed as
‘glasses’ to persons suffering from hypermetropia or long-sightedness. Long-sighted persons cannot
see nearby objects clearly unless they wear glasses made of converging lenses.
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A diverging lens is thinner in the middle and it will diverge a parallel beam of light:
diverging lens
Diverging lenses are used as the eyepiece of some terrestrial telescopes but they are more often
prescribed as ‘glasses’ for the correction of myopia or short-sightedness. Short-sighted persons
cannot see far-away objects clearly unless they wear glasses made of diverging lenses.
Worked Example:
The diagram below shows a ray of light incident on a glass prism.
triangular
prism
(a) Copy and complete the diagram to show how the ray of light is refracted into the glass. Label
the incident ray, the normal, the refracted ray, the angle of incidence (i) and the angle of
refraction (r),
(b) Draw the ray of light as it emerges out of the other face of the prism. Label this ray as the
‘emergent ray’.
normal
i
refracted
ray
r
incident
ray
emergent
ray
triangular
prism
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Form of energy
detected by the eyes
Water appears
shallower than it
actually is
Travels at
300,000,000 m/s in
vacuum
One which emits light
Sun, flame, lamp,
television screen
Travels in straight
lines
One which does not
emit visible light
speed
Lenses used as
glasses, in telescopes,
in microscopes and in
prisms
definition
examples
Properties of light
definition
Visible only because
they reflect light
incident on them
Luminous bodies
Moon, table, cinema
screen
examples
Applications of
refraction
Non-luminous
bodies
Optics
Incident ray, reflected
ray and normal, all lie
on same plane
Laws of reflection
first law
Ratio of sine of angle
of incidence to sine of
angle of refraction is
a constant, i.e
sin i
 cons tant
sin r
Laws of refraction
First law
Incident ray, reflected
ray and normal, all lie
on same plane
Second law
second law
Applications of
reflection
Characteristics of
image formed in
plane mirror
angle of incidence =
angle of reflection, i.e
i=r
Image is of the same
size as object
Vehicles have words
written laterally
inverted on them so
that they appear
correctly in rear-view
mirror
Image is laterally
inverted
The periscope
Rear-view mirror and
blind spot
Image is virtual
Image distance from
mirror=object
distance from mirror
Image is upright
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CHAPTER FIVE: ELECTRICITY
Electrical charge and electric current
Experiment 14: To distinguish between electrical conductors and electrical insulators.
Matter is made up of tiny particles called atoms. In its centre or nucleus, an atom contains two types
of tinier particles, called protons and neutrons. Another type of particles, called electrons, moves
round this nucleus in circular orbits.
Protons are said to be positively charged. Electrons are negatively charged. Neutrons are said to be
electrically neutral. Electrical charges are measured in a unit called coulomb (C) and they are
responsible for phenomena like lightning or electric currents that will make many electrical
appliances run.
Conductors and Insulators
An electrical conductor is a material that allows electricity to pass through it. Conductors contain a
large number of free electrons per unit volume. Examples are metals and graphite.
An electrical insulator is a material that does not allow electricity to pass through it. Insulators do
not contain enough free electrons per unit volume. Examples are glass, silk and plastics.
Current
Experiment 15: To measure current using an ammeter.
Current is defined as the rate of flow of charge per unit time.
𝐈=
𝐐
𝐭
where, I = current, in ampere (A),
Q = charge, in C,
t = time taken, in s
An electric current flow is similar to water flow through a pipe: just as we can measure the volume
of water flowing in one second for the water, we can also measure the number of electric charges
passing a point in one second. Electric current is measured with an instrument called an ammeter,
which is always connected in series.
Worked example:
A conducting sphere which has a charge of 120 C is earthed. It takes 60 s for the sphere to discharge
completely.
(a) Calculate the current flowing.
Q 120
Current, I = =
=2A←
t
60
(b) With which instrument will you measure this current and how will you connect it?
With an ammeter connected in series.
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Potential difference
Experiment 16: To measure potential difference using a voltmeter.
We define potential difference between two points as the energy converted from electrical into
other forms when one coulomb of charge passes between the points.
V=
W
Q
where V=e.m.f, p.d or voltage, in volts (V),
W=work done, in J,
Q=charge, in C.
Electric charges have to be given energy so that they can move inside wires. It is this same electrical
energy that will be converted into other forms of energy, for example, heat and light through a bulb.
This energy, that each coulomb of charge has, is called the voltage, potential difference (p.d) or
electromotive force (e.m.f). Potential difference is measured using an instrument called a voltmeter,
which is always connected in parallel.
Water will normally flow down a pipe because the two ends of the pipe are at different heights. The
larger the difference in height between its two ends, the faster the water will flow. Similarly, the
more energy we give to charges in a wire, the faster they flow in it: the larger the potential
difference applied across the wire, the larger will be the current. This was discovered by a scientist
known as Ohm.
Worked example:
A coil of copper is connected across the terminals of a battery of e.m.f 6 V. What is the chemical
energy transferred when 30 C of charge passes round the circuit?
Using V =
W
Q
Total energy transferred, W = VQ = 6 x 30 = 180 J ←
Electrical resistance and Ohm’s law
Electrons do not flow smoothly inside a metallic wire. In fact, they often collide against the metal
atoms and the latter offer resistance to their motion inside the wire. This opposition to the flow of
electrons and hence the current flow is called electrical resistance. If the metal is heated the
situation becomes worse for the electrons: now the metal atoms vibrate faster and makes it more
difficult for the current to pass through. A temperature rise increases the resistance of a metal.
But if the temperature remains fixed, the current flowing through the metal will double if we double
the potential difference across its ends. This is known as Ohm’s law which states that the current
flowing through a metal conductor is directly proportional to the potential difference across its ends
provided the temperature remains constant.
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The resistance of a material is defined as the ratio of the potential difference applied across it to
the current flowing through it.
𝐕 = 𝐈𝐑
where V=potential difference, in V,
I=current, in A,
R= resistance, in ohms (Ω)
Experiment to determine the resistance of a metallic conductor
Experiment 17: To determine the resistance of a fixed resistor.
battery
The apparatus is set up as shown.
switch
Variable
Resistor
(rheostat)
R
ammeter
A
V
voltmeter
The rheostat is set to maximum resistance so that a low current flows in the circuit. The circuit is
briefly closed and the voltmeter reading (V) and the ammeter reading (I) are taken. The resistance of
the rheostat is decreased in steps and several sets of potential differences and their corresponding
currents are noted. The results are tabulated as shown below:
Experiment Number
Voltmeter reading
V/V
Ammeter reading
I/A
A graph of potential difference (y-axis) against current (x-axis) is plotted as shown below:
p.d/V
current/A
The gradient of the graph gives the resistance of the metallic conductor in Ω.
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Resistors in series
Experiment 18: To demonstrate connections in series.
Resistors are tiny devices, often cylindrical in shape and with coloured bands on them. They are used
to control the current flowing in a circuit or to control the potential difference across them. If your
mobile phone operates on 3.6 V and you connect a battery of 4.5 V across it, it will be damaged after
some time. This is where resistances come into play: by arranging these resistances in a specific way
we can get exactly 3.6 V from a 4.5 V supply, and your mobile phone will last a lot longer!
The diagram shown below shows three resistors connected in series to a battery.
direction of
current
A
R1
R2
R3
V1
V2
V3
We can connect the ammeter anywhere round the circuit because the current is the same.
The p.d, however, does not remain the same. In fact,
p.d across the whole circuit=sum of p.d’s in the series circuit
𝐕 = 𝐕𝟏 + 𝐕𝟐 + 𝐕𝟑
But since the same current is flowing, the combined or effective resistance of all the resistors is
given by,
𝐑 = 𝐑𝟏 + 𝐑𝟐 + 𝐑𝟑
We can therefore connect resistors in series if we need a higher combined resistance.
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Resistors in parallel
Experiment 19: To demonstrate connections in parallel.
The diagram shown below shows three resistors connected in parallel to a battery.
V
I
A
I1
I2
I
I3
R1
R2
R3
The p.d across the battery is equal to the p.d across each of the resistors:
𝐕 = 𝐕𝐑 𝟏= 𝐕𝐑𝟐 = 𝐕𝐑 𝟑
Connections in the home are made in parallel so that the voltage remains the same.
The current, however, is not the same through each resistor:
main current=sum of currents through each resistor
𝐈 = 𝐈𝟏 + 𝐈𝟐 + 𝐈𝟑
But since the p.d does not change, the combined or effective resistance of the resistors in parallel is
given by:
1
1
1
1
=
+
+
R R1
R2
R3
We can therefore connect resistors in parallel if we need a lower combined resistance.
Worked example:
A number of 8 Ω resistors are available. Draw diagrams to show how you could connect a suitable
number of resistors to give an effective resistance of
(a) 24 Ω
X
8Ω
8Ω
8Ω
Y
Effective resistance across XY, RXY=8+8+8=24 Ω←
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(b) 4 Ω
8Ω
X
Y
8Ω
1
1 1 2
= + =
R XY 8 8 8
8
Effective resistance across XY, R XY = 2 =4Ω←
(c) 18 Ω
Connections in series can give the 16 Ω while the remaining 2 Ω can be obtained by a parallel
connection.
8Ω
8Ω
X
8Ω
8Ω
Y
8Ω
8Ω
1
8
1
8
1
8
1
8
Effective resistance across XY, R XY = 8 + 8 + ( + + + )−1=18 Ω←
Note: We can connect cells in series or in parallel. Connecting cells in series makes a battery of
greater e.m.f, but connecting them in parallel allows a larger current to flow in the circuit,
although it provides the same e.m.f.
3.0 V battery made of two 1.5 V
cells in series
Two 1.5 V cells in parallel
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Direct current (D.C) circuits
A direct current or d.c is a current which flows in one direction only, as opposed to an alternating
current (a.c) which constantly changes its direction of flow. Direct currents can be obtained from
cells, batteries or d.c power sources. A simple direct current or d.c circuit is an electrical circuit that
consists of a combination of batteries and resistors.
Worked example:
The circuit shown below consists of two 1.5 V cells connected to two identical lamps, each one
labelled 3.0 V. Each lamp has a resistance of 15 Ω at normal brightness.
1.5 V
1.5 V
— Dushan® +
— Dushan® +
lamp A
copper
wires
lamp B
(a) How are the cells connected?
In series.
(b) (i) How are the lamps connected?
In parallel.
(ii) What are the advantages of connecting the lamps in this way?
Both lamps will light up at normal brightness. If one lamp burns out, the other lamp will
continue to light up.
(c) (i) Use a circuit diagram to represent the circuit shown above.
3.0 V battery
—
+
0.4 A
Lamp A
Lamp B
0.2 A
0.2 A
(ii) Calculate the current flowing through lamp A.
Voltage of the battery= 1.5 + 1.5 = 3.0 V
Since the lamps are connected in parallel, voltage across each lamp = 3.0 V.
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Using V = I R,
V 3.0
=
= 0.2 A ←
R 15
(iii) What is the current flowing through the battery? Explain your reasoning.
A current of 0.2 A flows through lamp A and a current of 0.2 A flows through lamp B.
Both currents add up to (0.2 + 0.2) or 0.4 A and flow through the battery.
∴Current through the battery (also called ‘main current’) = 0.4 A←
Current through lamp 𝐀, I =
Note: Current always flows from the positive terminal to the negative terminal of a battery.
Safe use of electrical energy
Experiment 20: Wiring the three-pinned plug of an appliance to protect the appliance and its user.
DANGERS
HAZARDS
PREVENTIVE MEASURES
Damaged insulation
Live wire can come into
contact with the casing of an
electrical appliance, making it
live.
Overheating of cables may
melt the insulation causing a
short circuit, which may start a
fire.
Wet insulators will no longer
be good insulators, because
impure water is a good
conductor.
Earthe the metal casing and
put a suitable fuse and a
switch in the live wire.
Too many equipment
connected to one plug
Damp conditions
Use a suitable fuse to prevent
an excessively large current
from flowing through the
cable.
Appliance must be earthed.
Saving electrical energy
Much of our electricity is being generated by burning fossil fuels which are non-renewable and are
also responsible for global warming. We therefore need to save electricity if we want to live in a
healthy environment and if we want to avoid an energy crisis.
To save electrical energy:
1. Replace electrical heaters by solar heaters.
2. During the day, replace electrical lighting by natural lighting, by opening all window and door
curtains. Use energy-efficient light bulbs and fluorescent tubes rather than using filament
bulbs.
3. Use energy-efficient refrigerators and other electrical appliances.
4. Turn off unnecessary lighting and appliances as soon as they are no longer needed.
© 1995-2017 Dushan [δβ] BOODHENA
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measured in amperes
(A) with an ammeter
connected in series
rate of flow of charge
per unit time
Allow electricity to
pass through them
definition
Metals and graphite
formula
energy converted
from electrical into
other forms when
one coulomb of
charge passes
between the points
measured in volts (V)
with a voltmeter
connected in parallel
unit
examples
definition
Conductors
Do not allow
electricity to pass
through them
Glass, silk and plastics
formula
unit
Electric current
examples
Potential
difference
Insulators
current is directly
proportional to
voltage for ohmic
conductors
Ohm s law
Electricity
Earthe the metal
casing of an appliance
Electrical
resistance and
ohm's law
Safe use of
electrical energy
formula
V=IR
unit
Put a switch in the
live wire
Resistors in series
Resistors in
parallel
Same current
Put a suitable fuse in
the live wire
application
conclusion
Avoid damp
conditions in
electrical circuits
resistance measured
in ohms (Ω)
formula
formula
Same voltage
formula
conclusion
formula
Connections in the
home are made in
parallel
To decrease
resistance connect
resistors in parallel
To increase resistance
connect resistors in
series
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A
acceleration .................................................................. 13
air pollution .................................................................. 19
alternating current ........................................................ 39
alternative forms of transport ...................................... 23
ammeter ....................................................................... 33
analogue stopwatch........................................................ 9
angle of incidence ......................................................... 25
angle of reflection ......................................................... 25
apparent depth ............................................................. 30
average speed ............................................................... 13
end error ......................................................................... 4
energy ........................................................................... 19
energy-efficient light bulbs ..................................... 23, 40
F
first law of reflection ..................................................... 25
first law of refraction .................................................... 29
flow diagrams................................................................ 19
forms of energy ............................................................. 19
frictional forces ............................................................. 22
fuse ............................................................................... 40
B
G
beam balance.................................................................. 9
biomass ......................................................................... 20
blind spot ...................................................................... 27
glasses ........................................................................... 31
global warming ............................................................. 19
H
C
cameras ........................................................................ 30
cells in series ................................................................. 38
chemical energy ...................................................... 20, 21
clock ................................................................................ 9
conductors .................................................................... 33
connections in parallel. ................................................. 37
connections in series .................................................... 36
converging lens ............................................................. 30
cube ................................................................................ 7
cuboid ............................................................................. 7
current .......................................................................... 33
half-metre rule ................................................................ 6
human eye .................................................................... 30
hydroelectric energy ..................................................... 20
hypermetropia .............................................................. 30
I
instantaneous speed ..................................................... 13
Insulators ...................................................................... 33
K
kinetic energy................................................................ 21
D
dead space ...................................................................... 4
digital stopwatch ............................................................ 9
direct current ................................................................ 39
displacement .......................................................... 11, 12
displacement method ..................................................... 8
distance................................................................... 11, 12
distance-time graph ...................................................... 14
diverging lens ................................................................ 31
L
Lateral inversion ........................................................... 26
law of conservation of energy....................................... 21
length .............................................................................. 4
lenses ............................................................................ 30
light ............................................................................... 25
linear motion ................................................................ 11
long-sightedness ........................................................... 30
luminous body .............................................................. 25
E
earthing ........................................................................ 40
elastic potential energy ................................................ 21
electrical charge ............................................................ 33
electronic balance ........................................................... 9
electrons ....................................................................... 33
M
mass ................................................................................ 9
measuring tapes.......................................................... 4, 6
mercury ........................................................................... 8
metre rule ................................................................... 4, 6
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myopia .......................................................................... 31
N
negative accelerations .................................................. 14
neutrons ....................................................................... 33
non-luminous body ....................................................... 25
non-renewable energy sources .................................... 19
normal .......................................................................... 25
nuclear energy .............................................................. 20
O
scalar quantity .............................................................. 11
second law of reflection ................................................ 26
second law of refraction ............................................... 29
short-sightedness .......................................................... 31
slide projectors ............................................................. 30
solar energy .................................................................. 20
solar heaters ........................................................... 23, 40
speed ............................................................................ 12
speed of light ................................................................ 25
speed-time graph .......................................................... 15
sphere ............................................................................. 7
submarines.................................................................... 27
T
ohm’s law...................................................................... 34
P
parallax error .................................................................. 5
periscopes ..................................................................... 27
photocopying machines ................................................ 30
potential difference ...................................................... 34
potential energy ........................................................... 21
power............................................................................ 22
protons ......................................................................... 33
R
ray diagrams ................................................................. 28
real depth ..................................................................... 30
refraction ...................................................................... 29
renewable energy sources ............................................ 19
repeating measurements................................................ 4
resistance ...................................................................... 35
resistance (measurement) ............................................ 35
rheostat ........................................................................ 35
telescopes ..................................................................... 30
temperature .................................................................... 9
terrestrial telescopes .................................................... 31
thermometer .................................................................. 9
tidal energy ................................................................... 20
time ................................................................................. 9
V
vector quantity.............................................................. 11
velocity .......................................................................... 12
vernier callipers........................................................... 4, 6
vernier scale .................................................................... 5
virtual images ................................................................ 26
volume ............................................................................ 7
W
wind energy .................................................................. 20
work done ..................................................................... 20
S
Z
saving energy ................................................................ 23
saving fuel ..................................................................... 23
zero error ........................................................................ 4
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