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Waves

All waves carry energy from one place to another. There are two types of waves:

Transverse waves have vibrations perpendicular to the direction of travel (e.g. all electromagnetic waves).

Longitudinal waves have vibrations in the same direction as that in which they are travelling (e.g. sound waves).

All waves have the following:

Amplitude – the distance from the horizontal axis to the peak (in m).

Wavelength (λ) – the distance from peak to peak, or trough to trough (in m).

Frequency – the number of complete waves per second (in Hz).

Period – the time taken for one complete wavelength (in s).

All waves can be reflected, refracted and diffracted:

Reflection – a wave bouncing off a surface.

Refraction – a wave changing direction when it passes from one material to another..

Diffraction – a wave spreading out when it passes through a gap. Diffraction only occurs if the size of the gap is about the same as the wavelength of the waves.

The following formulae can be applied to all waves:

Amplitude and Pitch – Sound Waves

The amplitude of a wave is related to loudness or intensity - bigger amplitude means a louder sounds of higher intensity.

The wavelength is related to its pitch or intensity (a shorter wavelength means a higher pitch or intensity).

Sound is produced by objects vibrating - the strings on a violin, the surface of a drum the air in a trumpet, the reeds in an oboe.

We may view the vibrations on a cathode ray oscilloscope in the normal way. Not all sounds are audible to the ear. Dog whistles produce sound at too high a pitch for the human ear, but the sound can be heard by dogs. Ultrasound/sonar are frequency sound waves, used in industry, medicine and quality control.

Images may be formed using ultrasound and sonar by transmitting the waves, and observing the way in which they are reflected back.

P and S Waves P and S waves are seismic waves. The are produced during earthquakes. P-waves are longitudinal. They travel through solids and liquids and are fast.

S-waves are transverse. They will only travel through solids and are slower than p-waves.

Properties of reflection:

The angle of incidence is always equal to the angle of reflection.

An image formed by light waves in a plane mirror is virtual, laterally inverted, and the same distance from the mirror as the object.

Properties of refraction:

If a wave enters a denser medium (e.g. a perspex block), it will be bent towards the normal. The emerging ray will come out at the same angle, but displaced.

A prism can be used to split white light into the visible spectrum.

When a wave passes into a different medium, it will either slow down or speed up.

Properties of total internal reflection:

Total internal reflection is when a light wave wave reflects off the inside of a glass block, rather than refracting out of it.

he critical angle for perspex is about 43°.

This principle is used in fibre optics (e.g. with endoscopes in medicine).

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