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1. PROPERTIES OF WAVES
OBJECTIVES;
• Describe a wave in terms of speed, amplitude, frequency and
wavelength
• Identify differences transverse waves and longitudinal waves
• Calculate wave speed
• Describe reflection and refraction of waves
• Describe diffraction of waves

2. DESCRIBING WAVES
• A wave is any disturbance moving from one point to another carrying
energy through a medium without the medium as whole moving

3. WAVELENGTH AND AMPLITUDE
• The wavelength of a wave is the distance from one crest of the wave
to the next. Since the wavelength is a distance, it is measured in
metres, m. Its symbol is λ, the Greek letter lambda.
• The amplitude, A, of a wave is the maximum distance that the surface
of the water is displaced from its undisturbed level, that is, the height
of a crest (or the depth of a trough). Its symbol is A

4. FREQUENCY AND PERIOD
• The frequency, f, of a wave is the number of waves sent out each
second. Frequency is measured in hertz, Hz. One hertz (1 Hz) is one
complete wave or ripple per second.
• The period, T, of a wave is the time taken for one complete wave to
pass a point. The period is measured in seconds, s.

5. FREQUENCY AND PERIOD
• Frequency and Period are related to each other. Waves with a short
period have a high frequency.

6. WAVE SPEED
• Wave speed is the rate at which the crest of a wave travels.
• Waves can have very different speeds. Ripples in a ripple tank travel a
few centimetres per second. Sound waves travel at 330 m/s through
air. Light waves travel at about 300 000 000 m/s through air.

7. WAVES AND ENERGY
• When a wave travels from one place to another, it is not matter that
is moving. The wave is moving, and it is carrying energy. It may move
through matter or even through a vacuum, but the matter itself is not
transferred from place to place. A wave transfers energy without
transferring matter.
• Earthquakes show the huge amounts of energy which waves can
transfer. Vibrations passing through the Earth can cause buildings to
collapse. A seismometer records the vibrations caused by an
earthquake.

8. TRANSVERSE AND LONGITUDINAL WAVES
• Transverse waves: the particles carrying the wave move from side to side, at right
angles to the direction of propagation of the wave.
• Longitudinal waves: the particles carrying the wave move back and forth, along
the direction of propagation of the wave.
• Examples of transverse waves are ripples on water, light and other
electromagnetic waves, secondary seismic waves ( S – waves )
• Examples of Longitudinal waves are sound waves, primary seismic waves ( P –
waves )

13. ANSWERS

14. SPEED, FREQUENCY AND WAVELENGTH
• The speed, v, frequency, f, and wavelength, λ

17. CHANGING MATERIAL, CHANGING SPEED
• When waves travel from one material into another, they usually change speed.
• Light travels more slowly in glass than in air. Sound travels faster in steel than in
air. When this happens, the frequency of the waves remains unchanged.
• This means that their wavelength must change. This is illustrated in Figure 14.12,
which shows light waves travelling quickly through air. They reach some glass and
slow down, and their wavelength decreases. When they leave the glass, they
speed up, and their wavelength increases again.

20. ANSWERS

21. REFLECTION OF RIPPLES
• The figure below shows what happens when a flat barrier is placed in the ripple
tank. Straight ripples (plane waves) are reflected when they strike the flat surface
of the barrier. The barrier acts like a mirror, and the ripples bounce off it. This
shows an important feature of how waves behave. They pass through each other
when they overlap.
• The arrows show how the direction of the ripples changes when they are
reflected. The angle of incidence is equal to the angle of reflection, just as in the
law of reflection of light.
• The blue lines are called wavefronts . The separation of the wavefronts is equal to
the wavelength of the ripples

22. REFRACTION OF RIPPLES
• Refraction of light occurs when the speed of light changes. We can see the same
effect for ripples in a ripple tank. A glass plate is immersed in the water, to make
the water shallower in that part of the tank. There, the ripples move more slowly

23. DIFFRACTION
• It is the spreading or bending of a wave as the wave passes through a tiny gap or
meet an obstacle.
• Waves are diffracted when they pass through a gap or around the edge of an
obstacle.
• The size of the gap affects diffraction.
• The effect is greatest when the width of the gap is equal to the wavelength of the
ripples
• When the gap is much smaller than the wavelength, the waves do not pass
through at all.

24. DIFFRACTION
• Sound waves have wavelengths between about 10 mm and 10 metres. This is why
they are diffracted as they pass through doorways and windows.
• Light waves have a much shorter wavelength – less than a millionth of a metre.
This is why very small gaps are needed to see light being diffracted.
• Diffraction also happens as waves pass an edge. The greater the wavelength of
the waves, the greater the angle at which they are diffracted