1. Physics Notes GCE Study Buddy
WAVES
Physics Notes
GCE Study Buddy

2. Waves
Waves are repeated to-and-fro vibrations that transfer energy away from an energy source

3. Describing wave motion
Term
Description
SI units
Amplitude, A
The maximum displacement of the rope from the rest position
Metre (m)
Wavelength, λ
The shortest distance between 2 successive crests or troughs
Frequency, f
The number of complete waves produced per second
Hertz (Hz)
Period, T
The time taken to produce one complete wave
Second (s)
Wave speed, v
The distance travelled by a wave in 1 second

4. Describing wave motion
crest
trough

5. Types of Waves Transverse waves Longitudinal waves
The vibration of the particles in the medium is perpendicular to the direction in which the wave travels
Eg. water waves, rope waves, all types of electromagnetic waves including light waves, microwaves, X-rays, gamma rays
The highest point reached by a vibrating particle in a transverse wave is called crest or peak while the lowest point is called trough
Longitudinal waves
The vibration of the particles in the medium is parallel to the direction in which the wave travels
Eg. sound waves
The section in which the vibrating particles in a longitudinal wave are closest together is called compression while the section in which the vibrating particles are furthest apart is called rarefaction

6. Longitudinal and Transverse waves

7. Wavefronts
Any line or surface over which all the vibrating particles are in the same phase
Particles in the same phase have the same speed and are at equal distances from their source
In transverse waves, wavefronts are normally lines joining all the peaks at equal distance from their source
The distance between successive wavefronts equals a wavelength
The direction of travel of a wave is always perpendicular to its wavefronts as indicated by lines drawn perpendicular to the wavefronts.

8. Wavefronts

9. Wave Equation Velocity of wave, v = fλ
Example: The speed of light in vacuum is 3 x 108 m/s
Calculate the frequency of orange light, given that its wavelength in vacuum is 6 x 107 m.
3 x 108 = f x 6 x 10-7
f = (3 x 108)/(6 x 10-7) = 5 x 1014 Hz

10. Ripple Tank
The properties of waves in general and water waves in particular are most easily studied in a ripple tank

11. Reflection of waves
Waves are reflected when an obstacle is placed in their paths
All reflected waves obey the law of reflection which states
The angle of reflection equals the angle of incidence
The incident wave, the reflected wave, and the normal all lie on the same plane

12. Properties of reflected waves
The reflected wave the same wavelength, frequency, and speed as the incident wave
The velocities of the reflected and incident waves are different because they travel in different directions
The angle of reflection equal to the angle of incidence

13. Refraction of waves Waves are refracted when their speeds are changed
The speed of a wave is changed when the wave moves from a dense medium into a less dense medium or from deep water to shallower water
If the incident wave is travelling along the normal, it will continue to travel along the normal after entering water of a different depth
In all other cases, refraction produces a change in wave direction
On entering shallower water, the wave direction bends towards the normal.
On entering deeper water, the wave direction bends away from the normal

14. Refraction of water waves

15. Refraction of waves Properties Shallower to deeper water
Deeper to shallower water
Wavelength
Increases
Decreases
Frequency
Unchanged
Speed
Velocity
Direction of travel
Bends away from normal
Bends towards normal

16. Ripple Tank to show refraction of waves

17. Sound
Production of sound waves by vibrating sources: sound is produced by vibrating sources (eg tuning fork) placed in a medium (solid, liquid, gas)
Nature of sound waves
It is a form of energy that can be transferred from one point to another
It is an example of longitudinal waves consisting of compressions and rarefactions
Compressions are regions where air pressure is slightly higher than he surrounding air pressure
Rarefactions are regions where air pressure is slightly lower than the surrounding air pressure

18. Sound waves

19. Range of audible frequency
The range of frequency that a human ear can detect is from 20 Hz to 20,000 Hz

20. Transmission of sound in a medium
Sound waves require a medium for transmission
Sound waves cannot travel through a vacuum
Vacuum jar

21. Speed of sound in solid, liquid, gas
Medim
Speed in m/s
Air (gas)
300
Water (liquid)
1500
Iron (solid)
5000
Speed of sound changes with changes in temperature or humidity
Change in
Explanation
Temperature
Sound travels faster when temperature rises
Humidity
Sound travels faster when humidity increases
Pressure
A change in pressure does not affect speed of sound

22. Experiments to determine speed of sound in air
Pistol method
Observer A and B are positioned at a distance s apart and with a measuring tape, measure and record s. (must be more than 1km)
A fires a starting pistol
B starts the stopwatch on seeing the flash of the pistol and stops the stopwatch when he hears the sound
The time t, is recorded
The speed of sound v can be calculated by
Speed = distance / time
For better accuracy, the experiment should be repeated and the average speed of sound can be calculated.
The experiment can be repeated by interchanging the positions of A and B so as to minimise the effect of the wind direction.

23. Experiments to determine speed of sound in air
Echo method
Observer A and B are positioned at a distance s from the wall and with a measuring tape, measure and record s
A claps two wooden blocks.
On hearing the echo (reflected from the wall), he repeats the clap
B starts the stopwatch and also starts counting from zero till the nth clap.
The time interval tn is recorded
The average time between successive claps is t = tn/n
The speed of sound v can be calculated by
speed = distance/time

24. Reflection of sound An echo is a reflection of sound
Reverberation is the effect of a prolonged sound due to the merging of many echoes
Echoes are used in determining the depth of sea and locations of shoals of fish

25. Electromagnetic spectrum
The entire possible range of electromagnetic waves is called the electromagnetic spectrum

26. Properties of electromagnetic waves
They are generated by accelerating charged particles
They travel at 3 x 108 m/s in vacuum
They obey the laws of reflection and refraction
They show wave properties such as diffraction and interference
They obey the equation v = fλ
They are progressive transverse waves carrying energy in the form of oscillating electrical and magnetic fields vibrating at right angles to one another and to the direction of travel of the waves

27. Radiation Wavelength/m Sources Detectors Uses Ultraviolet 10-8 – 10-7
Gamma rays
10-15 – 10-11
Cosmic rays radioactive substances, nuclear changes
G M tubes with counters, bubble/cloud chambers
Checking welds, killing cancer cells in radiology, photography
X-rays
10-13 – 10-8
X-ray tubes: stopping of fast-moving electrons by a heavy metal target
Photographic film, fluorescent screen
X-ray photography, analysis of crystal structure
Ultraviolet
10-8 – 10-7
Mercury vapor lamps, sun, spark discharges
Fluorescent screens/dyes
Forgery detection, sun lamps
Visible light
10-7
Hot bodies, lasers, fluorescent screens, sun
Photographic film, photodiodes
Chemical spectral analysis, fibre optics
Infra-red
10-7 – 10-3
Warm bodies, sun, fires, furnaces
Blackened thermometers, thermocouples
TV remote control, radiant heaters
VHF and UHF (TV) waves
10-4 – 10-1
TV transmitters
Aerials and TV sets
Communications, entertainment
Radio waves
10-3 – 103
Radio transmitters
Aerials and radio sets
Radio, telescope, radar, communications