Physics
Waves and Radiation
Wave Characteristics
N4/5 Summary Notes
Content Level 4
SCN 4 – 20a
I have researched new developments in science and can explain how their current
of future applications might impact on modern life.
Content National 4
Wave characteristics
Comparison of longitudinal and transverse waves.
Frequency as the number of waves per second.
Wavelength and amplitude of transverse waves.
Use of numerical or graphical data to determine the frequency of a wave.
Use of appropriate relationship between wave speed, frequency and wavelength.
Use of appropriate relationship between distance, speed and time for waves.
Sound
Analysis of sound waveforms including changing amplitude and frequency.
Different methods of measurement of speed of sound in air.
Sound level measurement including decibel scale.
Noise pollution; risks to human hearing and methods of protecting hearing.
Applications of sonar and ultrasound.
Sound reproduction technologies.
Noise cancellation.
Content National 5
Wave Parameters and behaviours
Energy can be transferred as waves.
Determination of frequency, wavelength, amplitude and wave speed for longitudinal
and transverse waves.
Use of the relationships between wave speed, frequency, wavelength, distance and
time
Diffraction and practical applications
Comparison of long wave and short-wave diffraction
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Content Statements
Learning Outcomes
Wave Characteristics, parameters and behaviours
At National 4 level, by the end of this section you should be able to:
Wave Characteristics
 1. State the difference between longitudinal and transverse waves and
give examples of both.
 2. Define frequency as the number of waves per second.
 3. Identify and/or calculate the wavelength and amplitude of transverse
waves from a diagram.
 4. Use numerical or graphical data to determine the frequency of a wave.
 5. Carry out calculations using the relationship between wave speed,
frequency and wavelength.
 6. Carry out calculations using the relationship between distance, speed
and time for waves.
Additionally, at National 5 level:
Wave parameters and behaviours
 1. State that energy can be transferred as waves.
 2. Determine frequency, wavelength, amplitude and wave speed for
longitudinal and transverse waves.
 3. Carry out calculations using the relationship between wave speed,
frequency, wavelength, distance and time.
 4. Describe what is meant by diffraction and give practical applications of
the effect.
 5. Describe the differences between long wave and short wave diffraction.
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Learning Outcomes
Waves
All waves transfer energy.
All waves involve a movement of energy

Water waves

Sound waves

Light, radio, microwaves (electromagnetic spectrum
Transverse Wave
The particles move at right angles to the direction of energy transfer.
Water and all the waves on the electromagnetic spectrum are transverse waves.
Longitudinal Wave
The particles move parallel to the direction of energy travel
Sound waves are longitudinal waves.
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Wave PBC P 16, Q 1 - 4
4Wave Characteristics, parameters and behaviours
Wave Terms
Frequency
(f) the number of waves per second (Hertz) Hz
Wavelength
(λ) the distance from one point on a wave to the corresponding point on the
next wave (metres – m)
Amplitude
The height of a wave from middle to top (or middle to bottom) (metres – m)
Wavespeed
(v) The speed of the wave (m/s)
Period
(T) the time for one complete wave to pass a point. (seconds – s)
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5Wave Characteristics, parameters and behaviours
Waves PBC – Frequency P 2 – 3, Q 1 – 11; Wavelength P 4 – 6 Q 1 - 10
The Wave Equation
v= fλ
v = speed of wave (m/s)
f = frequency (Hz)
λ = wavelength (m)
Example 1
Find the speed of a wave with frequency
30Hz and wavelength 25cm
Example 2
A sound wave (v = 340m/s) has a
frequency of 60Hz. What is its
wavelength?
v= fλ = 30 x 0.25
= 7.5 m/s
v= fλ => λ = v/f
= 340/60
=5.7 m
Example 3
What is the frequency of a wave with
Example 4
What is the wavelength of SIBC?
speed 1500m/s and wavelength 20km ?
(96.2MHz)
v= fλ => f = v/λ
v= fλ => λ = v/f = 3 x 108/ 92.6 x 106
= 1500/20,000
= 3.24m
= 0.075Hz
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Wave Characteristics
Waves PBC P 7–11, Q 1 – 25; P 12-13, Q 1-3; P 14 – 15, Q 1 -11. Sound P 6-8, Q 1-10
Speed, Distance and Time
Speed = distance /time
speed = metres per second (m/s)
Distance = metres (m)
Time = seconds (s)
Example 1
What is the speed of a sound wave that
travels 6800m in 60 seconds?
Example 2
How long does it take a water wave to
travel 15m at 0.5 m/s?
v = d = 6800 = 113.3 m/s
t
60
t = d = 15 = 30s
v 0.5
Example 3
The sound of a horn is heard 1190m away,
3.5 seconds after it is sounded. What is
the speed of the horn sound in air?
Example 4
A boat sounds a foghorn and hears the
echo 4seconds later. How far is it from
the cliff?
Solution 1
d = vt = 4 x 340 = 1360m
v = d = 1190 = 340 m/s
t
3.5
Sound travel to cliff and back, so actual
distance = 1360/2 = 680 m
Solution 2
Time to cliff and back = 4s
Time to cliff = 4/2 = 2s
d = vt = 2 x 340 = 680m
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Waves PBC P 17 – 18 Q 1 – 9; P 19, Q 1 – 7. Sound P2, Q 1 – 6.
Wave Characteristics
Diffraction
Diffraction is the bending of waves round objects.
Long wavelengths diffract more than short wavelengths.
You can pick up long wave radio in the valley, but not short wave radio.
If the gap between
the barriers is less
than a wavelength you
get circular waves – if
it is more you get
straight wavefronts
with curved ends.
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Learning Outcomes - Sound
Learning Outcomes - Sound
At National 4 level, by the end of this section you should be able to:
Sound
 1. Recognise changes in amplitude and frequency from diagrams of sound
waveforms.
 2. Describe different methods of measuring speed of sound in air.
 3. State that sound level is measured in decibels (dB) and give typical
examples of readings on the decibel scale.
 4. Describe types of noise pollution, the risk it has to human hearing and
methods of protecting hearing.
 5. Describe applications of sonar and ultrasound.
 6. Describe what is meant by noise cancellation and give an example of its
use.
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Learning Outcomes - Sound
Analysis of Sound Waveforms
Wave diagrams (from oscilloscope)
High frequency - quiet sound
Low frequency -quiet Sound
High frequency - loud sound
Low frequency – loud sound
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Sound
Measuring the Speed of Sound
Experiment 1

Measure the distance between the person with the balloon and the
person with the stopwatch using a tape measure.

Start the timer when the balloon is seen to burst, then stop the timer
when it is heard going ‘pop’.

Speed = distance between people
Time on timer
Experiment 2

Measure the distance between the two microphones using a metre stick

Hit the piece of metal with the hammer.

The timer starts when the sound reaches microphone 1 and stops when
it reaches microphone 2.

Speed = distance between microphones
Time on timer
{Discussion regarding which is most accurate and how to improve
accuracy.}
The speed of sound in air
The speed of light in a vacuum
3 x 108m/s
340m/s
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Sound P 2 Q 1 - 6
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Sound
Sonar
Sonar or echolocation is when sound echoes are used to find the position of
objects. It stands for SOund NAvigation Ranging.
Bats, dolphins and other animals use this method to navigate or to find prey.
Fishing vessels use sonar to monitor the depth of water and to find shoals of
fish.
A ship uses its sonar to send out a pulse of sound and detects the reflected
pulses 0.2 seconds later. If the velocity of sound in water is 1500m/s, how deep
is the sea below the ship?
Method 1
Method 2
d = vt = 1500 x 0.2
Time for echo = 0.2s
= 300m
Actual depth = 300/2
Time to reach seabed = 0.2/2 = 0.1s
d = vt = 1500 x 0.1
= 150m
= 150m
The fishermen then pick up a pulse from a shoal of fish 75m below the ship –
how long does it take the sound to reach the fish?
t = d/v = 75/1500 = 0.05s
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Sound P 3, Q 1-2
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Sound
Ultrasound
Ultrasound is high frequency sound, above the range of human hearing
(20,000 Hz).
It is used to monitor the growth of unborn babies and can also detect the blood
flow through the heart, veins and arteries.
Ultrasound does not harm tissue.
A layer of jelly is placed between the skin and the transmitter/receiver to
prevent false echoes.
Ultrasound is used to measure the
depth of a baby in its mother’s
womb. The speed of ultrasound in
human tissue is 1500m/s. The time
between transmission and the
reflected signal is 1 x 10-4s.
a) How far did the sound
travel?
b) How deep is the part of the
baby which caused the
reflection?
a) d = vt = 1500 x 1 x 10-4
= 0.15m
b) Actual depth = 0.15/2
= 0.075m
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Sound P 4 – 5, Q 1-4
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Sound
Sound Level
Sound level is measured using a sound level meter.
The units for sound level are Decibels(dB)
Examples of noise levels
20dB
Whisper/ticking of watch/quiet country lane
40dB
Average house/normal private office
60dB
Conversational speech
80dB
Noisy office/electric shaver/alarm clock
100dB
Passing truck/car horn at 5m/ lawnmower
120dB
Thunder/fireworks display
140dB
Above threshold of pain. Jet engine around 40m away
Noise
What is noise pollution?
Unwanted loud or annoying sounds e.g. traffic noise, aircraft landing at
airports, building work
What noise level can damage hearing?
80dB Exposure to noise above 90dB is limited by law.
Protecting hearing
Hearing can be protected by wearing ear defenders or ear plugs, or by
avoiding loud sounds. You should avoid prolonged exposure to loud sounds
(including from headphones)
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Sound P 8 Q 1
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Sound
Sound Reproduction Technologies
Analogue and Digital Signals
Analogue signal
Digital signal
Speech signal
The wave produced by music and speech is an analogue signal.
Analogue waves can have any value.
MP3 players are digital devices, which means they use digital signals.
Digital signals are made from signals that have two values – 0 or 1.
Analogue to Digital Conversion
Sounds are turned into a digital signal by sampling the analogue wave at
regular intervals.
Sampling the sound wave produces a digital signal that is similar to the
original in shape.
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Sound
Sound Reproduction Technologies
Doubling the sampling rate improves the accuracy of the output wave.
The higher the sample rate the closer the digital signal sounds to the
original analogue signal.
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Sound
Noise Cancellation
Noise cancellation is the removal of unwanted sound.
e.g. the sound of the dentist’s drill
the sound of the engines on a boat or on an aeroplane.
How active noise cancellation (ANC) works
Two sound waves are added together in a process called ‘destructive
interference’
is
added
to
Cancellation wave
Sound wave
The two waves cancel out – producing silence!
A small microphone picks up the background noise, sends the signal
through an electronic circuit, which produces the cancellation wave.
This is called ‘active noise cancellation’ because it responds to changes
in the background sounds.
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Sound
Noise Cancellation
Noise cancelling headphones.
Padded ear cushion
- helps block
out noise
Microphone for
Springy
cancellation electronics
headband
-
keeps ear
cushions on
ears
The combination of the padded headphones and springy headband give
‘passive noise cancellation’. This just blocks sound – whether it is there
or not.
These headphones are useful when travelling, but they are also used by
airline pilots to help them hear radio conversations more easily.
The technology can allow patients to listen to their MP3 player without
hearing the drill when at the dentist. It is also being introduced by
some car manufacturers to improve passenger comfort.
In military applications personnel have found that there is a reduction
in stress and fatigue as well as an improvement in how easy
communications are to understand.
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Sound