Waves

We use waves to transfer energy and information. The direction of travel of the wave is the direction in which the wave transfers energy.

Transverse waves:

• The vibration of the particles is perpendicular to the direction in which the wave travels

Longitudinal waves:

• The vibration of the particles is parallel to the direction in which the wave travels.
• A longitudinal wave is made up of compressions and rarefractions

• Electromagnetic waves (e.g. light and radio waves), can travel through a vaccum. There are no particles moving in an electromagnet wave, as these waves are oscillations in electric and magnetic fields. The oscillations are perpendicular to the direction of travel of the wave. So all electromagnetic waves are tranverse waves.
• Mechanical waves (e.g. waves on springs and sound waves), travel through a medium. Mechanical waves may be transverse or longitudinal.
• Sound waves are longitudinal waves.

• The amplitude of a wave is the height of the wave crest or the depth of the wave trough from the position at rest.
• The greater the amplitude of a wave the more energy it carries.
• The wavelength of a wave is the distance from one crest to the next, or from one trough to the next.
• The frequency of a wave is the number of wave crests passing a point in one second. The unit of frequency is the hertz (Hz).
• The speed of a wave is given by the equation: v = f x
• v= wave speed
• f= frequency
•  = wavelenght

• The normal at a point on a surface is drawn perpendicular to the surface
• Angles are always measured between the light ray andthe normal
• The law 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 to pass through it.

• Refraction of light is the change of direction of a light ray when it crosses a boundary between two transparent substances
• If the speed is reduced refraction is towards the normal
• If the speed is increased refraction is away from the normal
• Different colours of light have different wavelengths, and are refracted by different amounts. when a light ray is shone onto a triangular glass prism a spectrum is produced. This is called dispersion.
• Violet is refracted the most, red is refracted the least.

• Diffraction is the spreading out of waves when they pass through 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