P6 - Revision Cards

Light and sound travel as waves. There are two types of waves - transverse and longitudunal. Waves can be described by their amplitude, frequency and wavelength. The speed of a wave can be calculated by its frequency and wavelength.

What are waves?

Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred. Some waves must travel through a substance. The substance is known as the medium, and it can be solid, liquid or gas. Sound waves and seismic waves are like this. They must travel through a medium. It is the medium that vibrates as the waves travel through.

Other waves do not need to travel through a substance. Visible light, infrared rays, microwaves and other electromagnetic radiation are like this. They can travel through an empty space.

Transverse waves

Light and other type of electromagnetic radiation are transverse waves. Water waves and S waves (a type of seismic wave) are also transverse. In transverse waves, the vibrations are at right angles to the direction of travel.

Longitudinal waves

Sound waves and waves in a stretched spring are longitudinal waves. P waves (a type of seismic wave) are also longitudinal wave. In longitudinal waves, the vibrations are along the same direction as the direction of travel.

Amplitude

As waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position. It is not the distance between the top and bottom of a wave. It is the distance from the middle to the top.

Wavelength

The wavelength of a wave is the distance between a point on one wave and the same point on the next wave. It is often easy to measure this from the crest of point one to the crest of the next wave.

Frequency (Hz, kHz, MHz, GHz)

The frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point  each second.

How fast do waves travel?

The speed of a wave - its wave speed (metres per seconf - m/s) - is related to its frequency (hertz - Hz) and wavelength (metre, m).

wave speed = frequency x wavelength

For example, a wave with a frequency of 100Hz and a wavelength of 2m travels at 100 x 2 = 200m/s.

The speed of a wave does not usually depend on its frequency or its amplitude.