# P6 - Revision Cards

waves and electrmagetic spectrum

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• Created by: lara
• Created on: 06-04-11 09:08

## What are waves

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

Other waves do not need to travel through a substance.Visible light, infrared rays, microwaves and other types of electromagnetic radiation are like this.They can travel through empty space. Electrical or magnetic fields vibrate as the waves travel through.

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## Transverse

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

Longitudinal

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

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## Amplitude, wavelength and frequency

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

The wavelength of a wave is the distance between a point on one wave and the same point on the next wave. Its often easiest to measure this from the crest of one waves to the crest of the next wave, but it doesn't matter where as long as it is the same point in each wave.

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. The unit of frequency is the hertz (Hz). For example, most people cannot hear a high-pitched sound above 20kHz, radio stations broadcast radio waves with frequencies of about 100MHz, while most wireless computer networks operate at 2.4GHz.

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## How fast do waves travel?

The speed of a wave - its wave speed (metres per second, m/s)- is related to its frequency (hertz, Hz) and wavelength (metre, m), according to this equation:

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.

Check your understanding of the equation by having a go at this activity.

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