Download Waves and Radiation Pupil Booklet

Crieff High School
National 5 Physics
Waves and Radiation
UNIT 3: WAVES AND RADIATION
Section 1: Wave parameters and behaviours
You should be able to:
1. state that energy can be transferred as waves.
2. determine the frequency, period, wavelength, amplitude and wave speed for longitudinal and
transverse waves.
3. use the relationships between wave speed, frequency, period, wavelength, distance and time
4. be able to explain diffraction and its practical limitations
5. compare long wave and short wave diffraction.
Section 2: Electromagnetic Spectrum
You should be able to:
1. describe the relative frequency and wavelength of bands of the electromagnetic spectrum with
reference to typical sources, detectors and applications.
2. be able to describe the qualitative relationship between the frequency and energy associated
with a form of radiation.
3. state that all radiations in the electromagnetic spectrum travel at the speed of light.
Section 3: Light
You should be able to:
1. explain how light is refracted at a boundary, identifying the normal, angle of incidence and
angle of refraction.
2. describe refraction in terms of a change of wave speed.
Section 4: Nuclear Radiation
You should be able to:
1. describe the nature of alpha, beta and gamma radiation.
2. describe the relative effect of ionisation, absorption and shielding.
3. list some sources of background radiation.
4. calculate absorbed dose and equivalent dose.
5. compare the equivalent dose due to a variety of natural and artificial sources.
6. describe some applications of nuclear radiation.
7. calculate the activity of a source in becquerels.
8. determine the half-life of a source using graphical or numerical data.
9. describe qualitatively the processes of nuclear fission and fusion.
10. state that nuclear fission and fusion processes are very important because of the generation of
huge amounts of energy.
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N5 Waves and Radiation Notes
Section 1 – Wave Parameters and Behaviours
Waves
A wave is any regular __________ or disturbance which carries __________ from one place to
another eg ripples spreading out on a _______, sound waves through the __________, radio and
_____ waves travelling through the air or empty space.
A wave is one way of transferring energy from place to place.
Measuring The Speed of Sound in Air
The speed of sound in air can be measured using the equipment below:
d
mic 1
mic 2
source of sound
electronic timer
1. Measure the ____________________________ using a ____________________.
2. Measure the _______________ taken for sound to travel from microphone 1 to microphone 2
using __________________________.
3. Calculate the ____________________ of sound using:
distance = speed of sound through air x time
Calculate the speed of sound in air using these typical results:
d = 100 cm = 1.0 m
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time, t = 0.00312 s
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N5 Waves and Radiation Notes
Measuring the Speed of Water Waves
Water tray
Stop clock
5 cm
2.5 s
desk
1. Measure the _________________ of the tray using a ___________________.
2. Drop the tray gently from a height of 5 cm and measure the ___________ it takes for one wave
to be reflected ______ times using a _____________________.
3. Calculate the total distance travelled.
4. Calculate the speed of the wave using:
Transverse and Longitudinal Waves
There are 2 types of wave:

___________________ eg sound waves

___________________ eg water waves, electromagnetic spectrum
Longitudinal waves: the direction of travel of wave is in the ___________ direction as the
propagation of the wave.
Transverse waves: the direction of travel of the wave is _______________________ the
direction of propagation of the wave.
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N5 Waves and Radiation Notes
Important Wave Quantities
Line of zero
disturbance
Amplitude (A): the distance between the line of zero disturbance and a __________ or ________.
Wavelength (λ): the length in metres from _________ to _________ or _________ to ________
or from any point on a wave to the same point on the consecutive wave.
It is usually given the symbol ‘λ’ pronounced ‘lambda’.
Frequency (f): the number of waves per ______________, measured in __________ (Hz).
frequency =
number of waves
number of seconds
f = N/t
Period of a Wave (T): the time it takes for one complete wave to pass a certain point.
Period = 1 / frequency
T = 1 /f
Wave speed or wave velocity (v): how fast the crests are moving. It is measured in ______.
Wave Formula: this is the relationship between wave speed, frequency and wavelength.
Wave speed = frequency x wavelength
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v = f x λ
N5 Waves and Radiation Notes
Summary
Quantity
Amplitude
Abbreviation
A
Unit
m
Wave speed
Frequency
Wavelength
Period of Wave
In some questions you will use the wave formula to calculate wave speed but in some questions
you will still need to use speed, distance and time.
Examples
a) A wave travels 50 m in 20 s. How fast is it travelling?
b) How fast do waves travel from a source of frequency 5.0 Hz and wavelength 3 m?
c) If 20 waves pass a point in 5 s what is their frequency?
d) What is the wavelength of waves of frequency 4.0 Hz travelling at a speed of 24 m/s?
e) Waves of wavelength 1.5 m travel at a speed of 9.0 m/s. What is their frequency?
f)
What is the period of the wave in question e?
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N5 Waves and Radiation Notes
Wave Traces on Cathode Ray Oscilloscopes
A cathode ray oscilloscope can be used to display waves of different frequencies on the screen.
The x-axis is the __________ axis.
The y-axis shows voltage.
Electrical signals can be displayed on a ____________________________ as shown below.
Oscilloscope screen
signal pattern
The shape of the signal pattern can be altered by changing the ______________ of the sound or
by changing the _______________ of the sound.
The loudness of the sound only affects the __________ of the waves on the screen ie
________ number of
waves - __________
height
initial sound
louder sound
The frequency of the sound only affects the ____________ of waves on the screen ie
________ waves –
the __________
height as before
initial sound
higher frequency sound
initial sound
this sound is ___________ but __________ pitched
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N5 Waves and Radiation Notes
The frequency of the wave can be calculated by measuring the time it takes for one complete
wave.
eg A trace is obtained on a CRO screen as shown below.
The dials are set as shown:
-
x-axis: 0.2 s per div
y-axis: 3 V per div
Calculate:
1. The peak voltage of the wave.
2. the frequency of the wave.
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N5 Waves and Radiation Notes
Diffraction of Waves
When waves reach an edge or a gap they ____________ round behind that edge. This effect is
called _________________.
The longer the wavelength, the _____________ the diffraction.
Complete the diagrams showing refraction at the edge of the barriers:
short wavelength
long wavelength
a little diffraction
more diffraction
Width of gap larger than wavelength
Wavelength similar to width of gap
Diffraction applies to all types of wave, not just water waves, eg sound waves bending round
doorways into the next room.
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N5 Waves and Radiation Notes
Diffraction in loudspeaker design.
Speakers that produce low frequency bass notes are called “woofers”. They need to move a lot of
air, so need to be quite large. Diameters of 30 cm or more are common.
However, a typical high treble note has a frequency of 5000 Hz or so, which corresponds to a
wavelength of almost 7cm – sound travelling at 330 m/s in air. This is much less than the diameter
we need for a woofer, so if we try to use the woofer to generate a high frequency note, the sound
wave will beam straight ahead without significant diffraction, just like water waves passing through
a wide gap. So, you won’t hear those notes unless you are right in front of the speaker.
It’s clear, then that the speakers which produce high frequency notes, called “tweeters”, must have
a much smaller diameter than required for the woofer.
A simple electric circuit inside the enclosure directs low frequencies to the woofer and high
frequencies to the tweeter.
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N5 Waves and Radiation Notes
Explain why houses located in some Scottish glens are able to receive radio signals but
have difficulty receiving TV signals using an ordinary roof top aerial.
Complete the diagrams to show how radio and TV waves diffract round hills
Radio Waves
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TV Waves
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N5 Waves and Radiation Notes
QUESTIONS ON SECTION ONE
1.
Six pupils in a 3rd year physics class go out to the playing fields to do an experiment on the
speed of sound through air. They measure out a distance of 250 m. They then each measure
the time for sound to travel this distance and get the following results:
0.70 s, 0.69 s, 0.74 s, 0.78 s, 0.67 s, 0.66 s
a)
What is the average time?
b)
What is the average speed of sound?
c)
Suggest why this answer is different from the accepted value.
d)
What could the pupils do to get a more accurate result?
2.
What is a wave?
3.
Label the following diagram correctly with: trough, crest, wavelength, amplitude
4.
What units are the following quantities measured in:
a)
b)
5.
Wavelength (λ)
Frequency (f)
In a swimming pool, a girl counts 15 waves passing her every minute. What is the frequency
of these waves?
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N5 Waves and Radiation Notes
6.
Certain water waves in a pond have a frequency of 5.0 Hz and a wavelength of 10 cm. What
is their speed?
7.
Waves take 20 s to travel from one end to the other end of a 50 m pool.
a)
what is their speed?
b)
what is their wavelength if the frequency is 0.5 Hz?
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N5 Waves and Radiation Notes
Section 2 – Electromagnetic Spectrum
The Electromagnetic Spectrum is a spread of waves (radiation) with similar properties but which
differ in wavelength and frequency.
increasing ___________
increasing ___________
All of these waves travel at the _________________________.
All of this radiation originates from the ________ and can travel through a __________________.
Most of these waves are _________________ to the naked eye. Humans can only detect light n
the range 400 – 700 nm.
Calculate the frequency of red light which has wavelength 700 nm.
Calculate the wavelength of radio waves which have frequency 320 kHz.
Calculate the wavelength of X-rays which have frequency 3 x 1017 Hz.
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N5 Waves and Radiation Notes
Sources of Electromagnetic Radiation and their Applications
Radiation
Source
Visible
Lasers
Infrared
Hot objects
Ultraviolet
Sunlight
Fluorescent lamps
Microwave
Microwave ovens
Radio
TV and radio masts
X-Ray
X-ray machines
CT scanners
Gamma
Radioactive isotopes of
different elements eg
cobalt-60
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Description of application or how it is detected
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N5 Waves and Radiation Notes
Energy and Frequency
High frequency radiation carries _________ energy than low frequency radiation.
eg ultraviolet radiation can cause damage to living cells and can cause skin _____________.
X-rays can penetrate soft material but are stopped by more dense material such as ___________.
X-rays and gamma rays have very high frequencies and so have enough energy to be able to
knock __________________ out of orbit around a nucleus in an atom.
This is called _______________________.
Diagram of ionisation:
When atoms in a living cell are changed in this way the cell becomes damaged. In large enough
doses _____________________ radiation can kill.
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N5 Waves and Radiation Notes
Section 3 – Light
All electromagnetic waves exhibit the following properties:
-
reflection
refraction
diffraction
interference
propagation
Refraction of Light
Light is _________________ as it passes from one medium into another eg air into glass, air into
water.
This is because there is a change in __________________ when waves are refracted. This
causes a change in the wavelength of the wave. It may also cause a change in ______________
of the wave.
When a ray of light passes into a more dense medium, eg from air into glass, the ray refracts
___________________________________.
When a ray of light passes into a less dense medium, eg from glass to air, the ray refracts
___________________________________.
Complete the following diagrams showing refraction in glass blocks:
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N5 Waves and Radiation Notes
Refraction and Apparent Depth
The apparent depth of a substance is the depth a transparent material ________________ to have
when viewed from above.
Eg a coin placed in a bowl of water appears to be ______________________ than it really is.
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N5 Waves and Radiation Notes
Critical Angle and Total Internal Reflection
When light hits a boundary at an angle greater than the _________________________, the light
does not pass through but instead is _____________________.
This is called total internal reflection since the ray stays __________ the glass.
air
glass block
This is the process used to send signals on a beam of light down an optical ____________ and in
__________________ used for internal medical examinations.
Optical Fibres
An optical fibre is a very thin ________ fibre, through which pulses of ________ can be transmitted
at very high speeds. Optical fibres are usually grouped together into thicker optical cables which
can carry a great many messages at the same time. Optical fibres are used in telecommunication
systems such as _____________.
The beam of light travels through the inside of an optical fibre by repeatedly _____________ off
the inside of the glass walls (total internal reflection).
Even when the fibre is bent round corners, the beam of light stays inside the fibre until it emerges
at the other _______.
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N5 Waves and Radiation Notes
Section 4 – Nuclear Radiation
All substances are made up of tiny particles called _________.
Atoms are made up of three kinds of even smaller particles:
- protons found in the ____________ of the atom. Protons have a ____________ charge.
- neutrons found in the ___________ of the atom. Neutrons have ________ charge.
- electrons which orbit around the nucleus. Electrons have a _____________ charge.
Labelled diagram of a helium atom:
Some substances are radioactive and emit nuclear radiation. They do this because their nucleus
is _____________ and breaks down emitting _______________ and / or energy. This is nuclear
radiation.
Types of Radiation
There are three types of nuclear radiation:
Type
Symbol
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Description
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Stopped / reduced by
N5 Waves and Radiation Notes
Ionisation
Atoms are normally electrically neutral as they have the same number of positive ____________
as negative _______________.
Ionisation is the process of causing an atom to gain or lose an ______________ which results in it
becoming a charged ________.
Ionisation occurs when an alpha particle collides with an atom and takes away an electron leaving
behind a positive ion.
Diagram of a charged ion:
Because they can be stopped in short distances, ______________________ produce much more
ionisation than beta particles or gamma rays.
Detecting Ionising Radiations
Nuclear radiation is often detected by the effects caused by ionisation eg:

a _____________________ tube detects α, β, and γ

photographic film is _____________ by ionising radiation

some substances give out flashes of ___________ called scintillations. These are
counted by a light detector and an electronic circuit.
Geiger-Mϋller tubes
window
radiation
counter
gas filled tube
A Geiger-Mϋller tube consists of a tube filled with ________ with a high ____________ passing
through it. Radiation causes the gas to _____________ and the electrons which are “knocked off”
are attracted to a ____________ plate and are counted by a ______________.
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N5 Waves and Radiation Notes
Film badges
These are worn by workers using radioactive materials. The radiation causes the photographic film
to go _____________. The different absorbing materials will allow different amounts of
____________ to pass through. The amount of fogging / blackening gives a measure of the
radiation exposure.
1 mm Al
3 mm Al
Lead
Open
window
plastic
Harmful effects of nuclear radiation
Ionising radiation can damage or change the nature of living cells. The risk of biological harm
from ionising radiations depends on:
1. the ______________________,
2. the type of ___________________.
3. the organ or ________________ exposed.
Absorbed Dose
Radiation emitted from a radioactive source may be absorbed by any material and the energy from
the particle is transmitted to that material. The _______________________ (D) depends on the
energy absorbed (E) by each ____________________ of material.
Absorbed Dose = energy absorbed
mass
The unit of Absorbed Dose is the __________ (Gy) which is equivalent to ___________________.
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N5 Waves and Radiation Notes
Equivalent Dose
A radiation weighting factor (wR) is given to each type of radiation as shown in the table.
Radiation
Weighting Factor w R
The Equivalent dose (H) is a measure of biological harm.
Equivalent Dose = absorbed dose x weighting factor
The unit of Equivalent Dose is the ________________ (Sv) which is also equivalent to
________________________.
(Units of millisievert (mSv) and microsievert (μSv) are often used.)
Humans can absorb up to 0.25 Sv without immediate ill effects; 1 Sv may produce radiation
sickness; and more than 8 Sv causes death. A typical yearly dose is 2.5 mSv.
Example – a worker in the nuclear industry receives the following absorbed doses:
0.30 mGy - γ rays
50 μGy - α particles
80 μGy - fast neutrons
a) List the 3 factors which affect the risk of biological harm from ionising radiations
z
b) Determine the equivalent dose received by the worker.
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N5 Waves and Radiation Notes
Activity of radioactive sources
Radioactive decay is a _______________ process.
Radioactive sources which give off more radiations per second are said to be more __________
than ones giving off fewer radiations per second.
The activity of a radioactive source means how many nuclei decay each second and is measured
in _____________________ (Bq).
One Becquerel is one _______________ per second.
Activity = number of decays
number of seconds
eg In a certain radioactive source, 7680 atoms decay in a time of 16 seconds. What is the activity
of that source?
The activity of any source ________________with time. This means that a dangerous source can
become safe after a long enough time. This decrease in activity can be shown in a graph.
Activity / Bq
Time
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N5 Waves and Radiation Notes
Background Radiation
Background radiation is all around us and is caused by _________________ sources and
_______________ sources.
Natural Sources
Artificial Sources
Background Radiation has a typical annual equivalent dose of ___________ per year.
Summary of Equations used in Nuclear Radiation
Quantity
Equation
Units
Absorbed Dose
Equivalent Dose
Activity
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N5 Waves and Radiation Notes
Half Life
The half-life of a source means the time taken for half the ____________in a sample to decay.
The half lives of radioactive materials ranges from fractions of a second to thousands of years.
Measurement of Half Life
1. Measure background count / second.
2. Place the Geiger tube close to the source and measure the count rate every 10 seconds for
__________________.
3. Subtract the ________________________ count rate from the measured count rate.
4. Plot a graph of corrected count rate against time.
Alternatively we can calculate half life without a graph.
eg. A source has an original activity of 12000 Bq. After 24 days the activity has dropped to only
750 Bq. What is the half life of the source?
12000
6000
T1
3000
T2
1500
T3
750
T4
_________ half lives have passed in 24 days.
One half life =
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N5 Waves and Radiation Notes
Eg 1 (from Virtual N5) A radioactive sample of bismuth has a half life of 60 minutes. The corrected
count rate from this sample at 9 am in the morning is 4000 counts / second.
a) State why the term “corrected” is used before count rate.
b) Determine the corrected count rate at 12 noon on the same day.
Eg 2 Determine the half life of the sample shown in the graph.
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N5 Waves and Radiation Notes
Fission and Fusion
Nuclear _____________ occurs when heavy nuclei, such as those in uranium or plutonium,
______________ apart. This process releases a huge amount of _________________. This
energy can be used in nuclear power plants to help generate _________________.
In some elements fission will occur spontaneously but in others they must be bombarded with
______________ before fission occurs. During this process more ______________ are released
which can cause more nuclei to split. This is called a _____________________ and keeps the
nuclear reaction going.
A nuclear power station uses ___________________ to absorb some of the neutrons. The control
rods control the __________ of the reaction.
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N5 Waves and Radiation Notes
Nuclear Fusion
In a fusion reaction, 2 light nuclei join together to make a _______________ nucleus. Vast
amounts of _______________ are released during a nuclear fusion reaction. However, this is a
clean process and no _____________________ or ______________________ waste are
produced.
Most fusion reactions take place in the ________. This is because it requires extremely high
___________________ to provide the energy to push the nuclei together. It is very difficult to
replicate this on earth as it is very hard to build containers that do not __________.
Diagram of a nuclear fusion reaction:
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N5 Waves and Radiation Notes