Waves transfer energy from one place to another through repeated vibrations. There are two main types of waves - transverse waves where the vibrations are perpendicular to the direction of travel, and longitudinal waves where the vibrations are parallel. Waves can be described using terms like amplitude, wavelength, frequency, period and speed. Waves reflect when they hit obstacles and refract when changing speed in different mediums. The electromagnetic spectrum ranges from gamma rays to radio waves, with visible light in between. All electromagnetic waves travel at the speed of light and have wave-like properties.

1. 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
Metre (m)
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 Second (s)

4. Describing wave motion
crest
trough

5. Types of Waves
• Transverse waves
o The vibration of the particles in the medium is perpendicular to the
direction in which the wave travels
o Eg. water waves, rope waves, all types of electromagnetic waves
including light waves, microwaves, X-rays, gamma rays
o 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
o The vibration of the particles in the medium is parallel to the direction in
which the wave travels
o Eg. sound waves
o 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
o The angle of reflection equals the angle of incidence
o 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
Unchanged
Speed
Increases
Decreases
Velocity
Increases
Decreases
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
o It is a form of energy that can be transferred from one point to
another
o It is an example of longitudinal waves consisting of compressions
and rarefactions
o Compressions are regions where air pressure is slightly higher than
he surrounding air pressure
o 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
o 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)
o A fires a starting pistol
o B starts the stopwatch on seeing the flash of the pistol and stops
the stopwatch when he hears the sound
o The time t, is recorded
o 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
o Observer A and B are positioned at a distance s from the wall
and with a measuring tape, measure and record s
o A claps two wooden blocks.
o On hearing the echo (reflected from the wall), he repeats the
clap
o B starts the stopwatch and also starts counting from zero till the
nth clap.
o The time interval tn is recorded
o The average time between successive claps is t = t n/n
o 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 Sources
/m
Detectors
Uses
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