GCSE Science/Waves

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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[edit]

Amplitude, a (m) 
The maximum disturbance of a wave from equilibrium.
Wave length, λ (m) 
The distance between a particular point on one wave and the same point on the next wave.
Frequency, f (Hz) 
The number of waves 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[edit]

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

Reflection[edit]

Reflection of waves is the change of direction caused when they bounce off a boundary (i.e. when they are reflected).

The Law of Reflection[edit]

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[edit]

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.

The Law of Refraction[edit]

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[edit]

Electromagnetic spectrum waves[edit]

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.

Radio waves 
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[edit]

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.

Answers[edit]

^ wavelength = speed / frequency = 3.75m