National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Waves & Radiation Summary Notes
Section 1 – Waves

(National 4)
Waves can transfer energy from one point to another.
Longitudinal Waves
A longitudinal wave vibrates along the same line as the direction of the
wave energy.
Sound energy is a longitudinal wave.
Transverse Waves
In a transverse wave the vibrations making up the wave vibrate at 90º to
the direction of the wave’s energy.
All members of the electromagnetic (em) spectrum are transverse
waves e.g. radio, microwaves, infra-red, light, ultraviolet, x-rays, gamma
rays.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
The Speed of Sound

(National 4)
The speed of sound in air is much less than the speed of light.
o Speed of sound in air is approx. 340 m/s
o Speed of light in air is approx. 300,000,000 m/s (3 x 10 8 m/s)

An example of this is when a flash of lightning (light) is seen before the
thunder (sound) is heard, although both were produced at the same time.
Measuring the Speed of Sound
o
o
o
o
Make a loud sound (bell) near 1st microphone.
When the sound reaches 1st microphone the electronic timer starts.
When the sound reaches 2nd microphone the electronic timer stops.
Measure the distance (d) between the microphones.
Speed of sound (m/s) =
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distance (m)
time on timer (s)
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
How sound energy is transferred
(National 4)
Speed, Distance and Time (sound waves)
speed = distance
time



d
v
t
d=vxt
v=d/t
t=d/v
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Speed (v)
measured in (m/s)
Distance (d) measured in (m)
Time (t)
measured in (s)
National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Wave Terms
(National 4)
Wavelength, 
(m)
● Distance from one point on a wave to the same
point on the next wave.
Amplitude, a
(m)
● Size of maximum disturbance from centre (zero)
position. The greater the amplitude, the more
energy in the wave.
Frequency, f
(Hz)
● Number of waves passing a point each second.
Frequency = number of waves
time (seconds)
Wave speed, v
(m/s)
●Distance travelled by the wave in one second.
Speed = distance travelled (m)
time (seconds)
Period, T
(s)
●Time taken for one wave to pass a point
Period = time  number of waves.
T
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1
f
or
4
f 
1
T
National 4/5 Physics
Waves & Radiation – Section 1 - Waves
The Wave Equation
(National 4)
Speed = frequency x wavelength
V =
(m/s)
f
(Hz)
x
Wave speed
(m/s)
Wavelength
(m)
v
Wave frequency
(Hz)

(m)

f
Equivalence of v = f and v= d/t
(National 5)
Waves move a distance of one wavelength () in a time equal to one period
(T).
So when d =  then t = T
However, T =
1
f
Therefore if v 
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d

, v
1
t
f
 f
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Wave Patterns
(National 4)
The greater the frequency of a sound wave, the higher the pitch of the sound.
 The greater the amplitude of a sound wave, the more energy it
has, therefore, the louder it is.
 Electrical signal patterns in telephone wires show the same
changes as those for sound signals when loudness and
frequency are altered.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Sound Level
(National 4)
The human ear can be damaged by prolonged exposure to very loud
sounds. We can measure the sound intensity using a sound level
meter.
 Sound level is measured in decibels (dB)
 Sound levels over 80dB are considered to be noise pollution
which could cause damage to our hearing over a prolonged
period, so ear defenders should be worn.
The picture below gives typical sound levels in our everyday lives.
The least sound intensity our ears can detect is 0 dB.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Ultrasound


(National 4)
The frequency range for human hearing is 20 – 20,000 Hz.
High frequency sound beyond this range is called Ultrasound.
The pictures below show how ultrasound is used in industry, medicine and
nature.
o Ships can measure water depth using ultrasound
o Ultrasound can be used to shatter kidney stones.
o Bats move around using ultrasound
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Ultrasound Calculations
(National 5)

An ultrasound pulse is transmitted by a wave generator which
acts as both a transmitter and a receiver.

When calculating the distance travelled by the ultrasonic wave,
we must remember that the wave is reflected off an object and
travels back to the generator (receiver)
e.g An ultrasonic pulse takes 0.4s to travel to the sea bed and
back to the wave generator. If the speed of sound in water is
1500m/s, calculate the depth of water beneath the ship.
v = 1500m/s
t = 0.4s
d=?
d=vxt
d = 1500 x 0.4
d = 600m
Distance from ship to the sea bed and back up is 600m.
Therefore, distance from ship to sea bed is 300m.
Depth of water below ship is 300m.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Doppler Effect



(National 5)
The Doppler Effect is a perceived change in frequency and
wavelength of a wave.
The effect occurs when an object generating waves moves
towards and past you, as you remain stationary.
The effect also occurs when you travel towards or away from a
stationary source of waves.
If the source of a wave gets closer to you, and you are standing still, then
you hear the frequency get higher and the wavelength shorter. An example
of this is when an express train rushes towards you whilst you stand still
on the station platform.
o As the train approaches, the perceived pitch of the sound
coming from the train increases.
If the source of a wave moves away from you, and you are standing still,
then you hear the frequency get lower and the wavelength longer.
o As the train moves away, the perceived pitch of the sound
coming from the train decreases.
Remember the pitch of the sound being produced by the train never
changes – you just hear that it does!
High Pitch
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Low Pitch
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Diffraction
(National 5)

Diffraction is ‘the bending of waves around obstacles.’ All waves
diffract to some extent, but longer wavelengths diffract more than
shorter wavelengths.

Radio waves have a longer wavelength than television waves and
therefore can bend round obstacles such as hills, buildings or
trees more easily.
Therefore radio reception is better than television reception in
such areas.
(The distance between the lines represents the wavelength.)
In the diagram above, you can see that the longer wavelength is much
better at bending round the obstacle than the shorter wavelength.
LONG WAVELENGTHS DIFFRACT BETTER THAN SHORT WAVELENGTHS.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Reflection

(National 5)
The Law of Reflection states that :
‘The angle of incidence is equal to the angle of reflection’
Refraction
(National 5)
Refraction occurs when light moves from one medium to another and
changes direction due to a change in its speed.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Examples of Refraction
(National 5)

When the light ray enters a denser medium e.g. air to glass, it bends
towards the normal due to its speed decreasing.

When the light ray enters a less dense medium e.g. glass to air, it speeds
up, and as a result, bends away from the normal.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Applications of Refraction
(National 5)

Refraction of light through lenses can be used to correct sight
defects.

Short sight (Myopia) can be corrected using a concave lens.

Long sight (Hypermetropia) can be corrected using a convex lens.
Short Sight
Long Sight
Remember!

With short sight, light comes to a focus in too short a time.
Corrected with a concave lens.

With long sight, light comes to a focus in too long a time.
Corrected with a convex lens.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Power of a lens
(National 5)
 The power of a lens is a measurement of how good the
lens is at changing the direction of the light ray (i.e. a
measurement of refraction)
 The power is measured in Dioptres (D)

Power = 1 ÷ focal length (m)
1
Power (D)
Focal length (m)
P
f
 Thick lenses have a short focal length.
 Thin lenses have a long focal length.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Total Internal Reflection

(National 5)
When light travels from a denser medium to a less dense medium
e.g. glass to air, and the angle of incidence in glass gives a refracted
angle of 90º in air, then the angle in of incidence in the glass is called
the ‘critical angle’
Refracted Ray
ic
IncidentRay
Ray
Incident

If the angle of incidence is greater than the
critical angle, Total Internal Reflection occurs
at the glass to air boundary.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Applications of Total Internal Reflection
Fibre Optics
‘Cat’s Eye’ retro-reflectors
Periscopes
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(National 5)
National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Section 2 – Radiation
Electromagnetic Spectrum
(National 4)
Detectors of Radiation
Radio & TV waves: aerials, radio telescopes.
Microwaves: aerials, radio telescopes.
Infra-red: thermometers, thermograms.
Visible Light: photocells, photodiodes, the
human eye.
Ultra-violet: photographic film, photocells,
fluorescence of certain chemicals.
X-rays: photographic film, ionisation chambers,
fluorescence of certain chemicals.
Gamma-rays: GM tube, photographic film,
gamma camera.
(National 5)
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
All electromagnetic waves travel at the
speed of light 300,000,000m/s

Electromagnetic waves can travel
through a vacuum.

The frequency of the electromagnetic
waves increases from radio waves to
gamma rays.

The higher the frequency, the more
energy delivered by the radiation.
National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Radiation


(National 4)
Radiation is all around us.
Radiation can come from natural sources and artificial sources.
Natural Sources
Cosmic radiation (Sun, outer space)
Radiation from the Earth’s crust
Radiation from the human body
Artificial Sources
Nuclear power stations
Nuclear medicine ( X-rays, radiography)
Testing nuclear weapons

The radiation all around us from both natural and artificial sources is
known as Background Radiation

Uses of nuclear radiation
Medical
Destroying cancerous
tumours,
(gamma radiation)
Diagnosing problems inside
the body
(gamma cameras)
Sterilising medical equipment
Industrial
Nuclear power stations
Finding faults in building materials and sources of
pollution/leaks
Smoke alarms

Radiation can damage living cells.

Various precautions will reduce the harmful biological effects of radiation:
o Increasing the distance between the radiation source and person.
o Reducing the exposure time to radiation source.
o Wearing shielding e.g. lead apron
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Radiation
(National 5)
Some elements in the periodic table are radioactive. This is due to the
nuclei of the atoms within that element disintegrating and emitting
radiation.

Alpha
Emitted from the nucleus.
2 protons (+ charge)
2 neutrons (0 charge)
Beta
Gamma





An electron ( - charge)
Emitted from the nucleus when
a neutron changes into a
proton, emitting an electron.

An electromagnetic wave.
Emitted from the nucleus.
These are ionising radiations.
Ionisation occurs when an atom loses or gains an electron.
Removing and electron creates a positive ion, and adding an
electron creates a negative ion.
Alpha radiation is the most ionising since it is positively charged,
and therefore seeks electrons. If it removes an electron a positively
charged ion is left behind.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Absorbers
(National 5)
.
o Alpha can be absorbed by a few centimeters of air or a piece of
paper.
o Beta can be absorbed by approx 5mm of Aluminium.
o Gamma can be absorbed by a few centimeters of Lead.
Activity of a radioactive source
o The activity of a radioactive source is a measurement of the number
of nuclear disintegrations each second.
o Activity is measured in Becquerel’s, (Bq)
Activity A = N, number of Disintegrations
(Bq)
t, time (s)
o The activity of a radioactive source decreases with time.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Radiation
(National 5)
Half – Life
When a radioactive source disintegrates, the activity (number of
disintegrations per second) depends only on the number of radioactive
nuclei present, so the greater the number of nuclei disintegrating each
second, the greater the activity of the source.
o The ‘half-life’ of a radioactive substance is the time taken for half of
the radioactive nuclei to disintegrate i.e. the time taken for the
activity of the radioactive source to fall to half of its original value.
o We can find the half-life of a radioactive source from an Activity/time
graph.
o The half-life of a radioactive source is a constant value for a
radioactive source.
o Half-life can be measured in seconds, minutes, hours, days or years.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Radiation
(National 5)
We can also find the half-life using numerical data:
A radioactive isotope gives an initial count rate of 1800 Bq,
after 120 minutes the activity is 225 Bq, calculate the half-life.
Activity (Bq) 1800 900 450 225
Time (mins)
0
T1/2 T1/2 T1/2
3 half-lives (T1/2) = 120 minutes, therefore T1/2 = 40 minutes.
Absorbed Dose (D)
o The effects of absorbed radiation depend not only on the amount of
radiation absorbed, but the mass of the object which absorbs it.
o The term ‘absorbed dose’ is a scientific term and is defined as the
energy per unit mass. It is measured in Grays (Gy).
Absorbed Dose = Energy absorbed ÷ mass of absorbing material
Joules
(J)
E
Grays
(Gy)
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m
D
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Mass
(kg)
National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Equivalent Dose (H)
(National 5)
o The biological risk caused by the absorption of radiation is
represented by a quantity called the ‘Equivalent Dose’. Equivalent
Dose is measured in Sieverts, (Sv)
o The Equivalent Dose takes into account not only the energy of the
radiation, but the type of radiation being absorbed.
o Each type of radiation (,,) is given a radiation weighting factor, Wr.
Radiation
Radiation Weighting factor (wr)
20
Alpha 
1
Beta 
1
Gamma 
Fast neutrons
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Equivalent Dose (H)
Equivalent Dose
(Sv)
H
Absorbed Dose
(Gy)
D
wr
Radiation
Weighting Factor
(No units)
To calculate the Equivalent Dose when a person is exposed to more
than one type of radiation, we calculate the equivalent dose for each
type of radiation using the above equation and add them all together.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Example
(National 5)
A worker is exposed to:
o 15mGy of gamma radiation
o 400Gy of alpha particles
o 600Gy of beta particles
Wr = 1
Wr = 20
Wr = 1
Calculate the total Equivalent Dose received by the worker.
Gamma : H = DWr
H = 15 x10-3 x 1
= 15 x10-3 Sv
Total H = (15 + 8 + 0.6) x 10-3 Sv
= 23.6mSv
Alpha : H = DWr
= 0.0236Sv
H = 400 x 10-6 x 20
= 8 x 10-3 Sv
Beta
: H = DWr
H = 600 x 10-6 x 1
H = 0.6 x 10-3 Sv
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Radiation
(National 5)
Fission
In a fission reaction, a large unstable nucleus splits into two smaller
nuclei with the release of several protons and energy.
o Fission can be spontaneous, where it occurs randomly in nature, or
it can be stimulated.
o In a stimulated fission reaction, which occurs in nuclear reactor core,
the large uranium nucleus is struck by a moderated neutron, forcing
it to fission (split) into as shown in Figure 1 above.
o If the mass before the fission reaction and the mass after fission are
calculated, there is always some missing mass as a result of fission.
o The missing mass is known as ‘lost mass’ and is changed into pure
energy according to Einstein’s famous equation
E = mc2
E = energy released (J)
m = ‘lost mass’ (kg)
c = speed of light ( 300,000,000m/s)
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Radiation
(National 5)
Fission
o A fission reaction occurs inside a nuclear reactor.
o The neutrons released go on to create more fission reactions.
o This is called a Chain Reaction. The chain reaction can be
stopped by absorbing the neutrons using control rods.
o The energy released in a reactor’s core is used to raise steam,
which turns a turbine which spins the generator rotor, producing
electricity.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Radiation
(National 5)
Fusion
In a fusion reaction, two light nuclei combine to form one larger nucleus
and energy is given out in the process.
o If the mass before the fusion and the mass after the fusion are
calculated, there is always some missing mass.
o The missing mass is changed into energy according to Einstein’s
famous equation
E = mc2
E = energy given out (J)
m = ‘lost mass’ (kg)
c = speed of light (300,000,000 m/s)
Deuterium and Tritium are isotopes of Hydrogen. During fusion, they
form a nucleus of Helium and a neutron.
The two smaller nuclei need to collide at very high speeds for fusion
to occur. In practice this means raising the temperature of Hydrogen
gas to a staggering 100 million degrees Celsius. This happens
naturally in our sun.
Scientists have found this reaction very difficult to replicate on Earth
due to the high temperatures needed. If we could harness the energy
from fusion the world’s energy worries would be over.
10 grams of Deuterium, which can be extracted from 500 litres of
water and 15g of Tritium produced from 30g of Lithium, would
produce enough fuel for the lifetime electricity needs of an average
person in an industrialized country.
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National 4/5 Physics
Waves & Radiation – Section 1 - Waves
Radiation
Natural
occurrence
By products
of the
reaction:
Energy ratios:
Conditions:
Energy
requirement:
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(National 5)
Nuclear Fission
Nuclear Fusion
Fission reaction does not
normally occur in nature.
Fission produces many
highly radioactive particles.
Fusion occurs in stars,
such as the sun.
Few radioactive particles
are produced by fusion
reaction.
The energy released by
fusion is three to four times
greater than the energy
released by fission.
The energy released by
fission is a million times
greater than that released in
thermal chemical reactions;
but lower than the energy
released by nuclear fusion.
Fission reaction occurs
inside nuclear piles within a
concrete and lead reaction
vessel.
Takes little energy to split
two atoms in a fission
reaction.
29
Very high temperatures are
required.
Extremely high energy is
required to bring two or
more protons close enough
that nuclear forces are
overcome and the nuclei
fuse together.