Physics-Waves

The nature of waves

• We use waves to transfer energy and to transfer information
• Transeverse waves vibrate at right angles to the direction of energy transfer. All electromagnetic waves are transverse waves
• Longitudinal waves vibrate parallel to the direction of energy transfer. A sound wave is a longitudinal wave
• Mechanical waves, which need a medium (substance) to travel through, may be transverse or longitudinal waves

Measuring waves

• For any wave, its amplitude is the height of the wave crest or the depth of the wave trough from the position at rest
• For any wave, its frequency is the nmber of wave crests passing a point in one second 
• For any wave, its wavelength is the distance from one wave crest to the next wave crest. This is the same as the distance from one wave trough to the next wave trough
• v=f x (upside down y)
• v is the wave speed in metres perf second, m/s
• f is the frequency in hertz, Hz
• (upside down y) is the wavelength in metres, m

Wave properties: reflection

• The normal at a point on a surface is a line drawn perpendicular to the surface
• Angles are always measured between the light ray and the normal
• The law of reflection states that: the angle of incidence is equal to the angle of reflection
• A real image is one that can be formed on a screen, because the rays of light that produce the image actually pass through it
• A virtual image cannot be formed on a screen, because the rays of light that produce the image only appear tp pass through it

Wave properties: refraction

• Refraction of light is the change of direction of alight ray when it crosses a boundary between two transparent substances
• If the speed is reduced, refraction is towards the normal (e.g. air to glass)
• If the speed is increased refraction is away from the normal (e.g. glass into air)

Wave properties: diffaction

• Diffraction is the spreading out of waves when they pass throguh a gap or round the edge of an obstacle
• The narrower a gap the greater the diffraction
• If radio waves do not diffract enough when they go over hills, radio and TV reception will be poor

Sound

• The frequency range of the normal human ear if from about 20 Hz to about 20 kHz
• Sound waves are longitudinal
• Sound waves need a medium in which to travel
• Reflections of sound are called echoes

Musical sounds

• The pitch of a note increases if the frequency of the sound waves increase
• The loudness of a note depends on the amplitude of the sound waves
• Vibrations created in an instrument when it is played produce sound waves