# GCSE Science/Waves

Most forms of energy (e.g. sound, light, heat) travel by means of waves. All waves are produced by some kind of vibration. The direction of the vibration in relation to the direction of the wave determines the type of wave.

There are two types of wave:

• Transverse waves - produced by vibrations which are at right angles to the direction of the wave. The majority of waves fall into this category. Examples of this type of wave include light, heat and radio waves.
• Longitudinal waves - produced by vibrations which are in the same direction as the direction of the wave. Examples include sound waves and P-wave seismic waves.

## Wave Definitions

Amplitude, a (m)
The maximum disturbance of a wave from equilibrium. This can be described as the displacement from the rest position to the crest.
Wave length, λ (m)
The distance between a particular point on one wave and the same point on the next wave. It is the length of a full cycle of a wave (eg. from trough to trough).
Frequency, f (Hz)
The number of complete cycles (oscillations) passing a particular point in one second.
Period, T (s)
The time taken for one wave to pass a point.
Speed, v (m/s)
Distance travelled by the wave in one second. speed = frequency * wavelength

Test YourSelf 1 Light travels at 300 million m/s. What is its wavelength if the frequency is 80 megaHz? [1]

## Properties of waves

All waves have 3 main properties: reflection, refraction, and diffraction.

### Reflection

Reflection of waves is the change of direction caused when they bounce off a boundary (i.e. when they are reflected). Reflection of light allows us to see objects, as light bounces off them into our eyes.

#### The Law of Reflection

The Law of Reflection states that 'the angle of incidence (i.e. the angle at which the ray strikes the boundary) is equal to the angle of reflection (i.e. the angle at which the reflected ray leaves the boundary)'

### Refraction

Refraction of waves is their change of velocity (i.e. change in speed or direction) when they travel through a different medium. This can be illustrated with water. Waves only refract if they meet the new medium at an angle. if they are travelling along the normal, they change speed but not direction (aren't refracted)

#### The Law of Refraction

The Law of Refraction states that for a wave entering a denser medium 'the angle of incidence is greater than the angle of refraction'. This is because the wave slows down, and thus bends towards the normal.

## Groups

### Electromagnetic spectrum waves

All electromagnetic waves travel at the speed of 299,792,458 m/s (~300,000 km/s). Electromagnetic waves do not need particles to travel through - for example, sunlight can travel through vacuum. Electromagnetic spectrum waves are a typical example of transverse wave radiation.

Used for transmitting radio and TV data.
Microwaves
Vary from TV, radars, communications to cooking. Ranges from 1GHz to 300GHz. See the Uses
Infra-red
Transmit heat. See the Uses
Light
Transmit visible light
UV
Ranges from... See the Uses
X-ray
Used in hospitals and ... . Ranges from 30 to 3000 PHz (10^15 hertz)
Gamma
A form of higher energy and frequency X-ray.

### Sound/Ultrasound

Sound waves are longtitudinal waves that need particles to travel through. Range from 0Hz to 20kHz Ultrasound are waves with frequency higher than 20kHz, which are above the human hearing range. Used in fishing, hospitals and cleaning.