# The Electromagnetic Spectrum - AQA GCSE Physics Core

Revision notes on everything to do with the electromagnetic spectrum

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• Created by: Sophie
• Created on: 03-01-12 16:51

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The Electromagnetic Spectrum:
Electromagnetic waves are electric and magnetic disturbances that transfer energy from one place to
another.
Gamma rays
Xrays
Ultraviolet
Visible Light
Infrared
Microwaves
Wavelength:
The wavelength is the distance form one wave peak to the next wave peak
along the waves
Radio waves have the longest wavelengths of more than 1km.
Xrays and gamma rays have the shortest wavelengths of less than a millionth
of a millionth of a metre (= 0.000,000,000,001m)
Frequency:
Frequency of an electromagnetic wave is the number of complete waves
passing a point each second.
This is measured in Hertz (Hz), Kilohertz (kHz) and Megahertz (MHz)
I Hertz = 1 complete wave per second
Gamma rays have the highest frequency
Radio waves have the lowest frequency
The speed of electromagnetic wave:
All electromagnetic wave travel at the speed of light (300million m/s) through space or a vacuum.
We can work out the wave speed using frequency and wavelength:
Wave speed = Frequency X wavelength
(m/s) (Hz) (m)
Other equations:
Frequency = 1
Time period of 1 wave
Time of 1 wave = 1
Frequency
Gamma Rays:
Gamma rays are used for:
Killing harmful bacteria in food
Sterilising surgical instruments
Killing cancer cell ­ they direct a narrow beam of gamma radiation at the
cancerous cells. The beam is aimed at it from different directions on order to
kill the tumour but not the surrounding tissue
Gamma rays can also be dangerous because they can cause cancer as well as killing it. Small doses
of gamma radiation can cause cell mutation by damaging the DNA. High doses can kill living cells.
Xrays:
Xrays pass through soft tissue but are absorbed by bones and thick metal plates.
Xrays are used to take pictures of bones.
Xrays from xray tubes are directed at the patient and a light proof cassette containing
photographic film is placed the other side.

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When the xray tube is switched on, xrays pass through the patient's body. They leave a shadow
image on the film showing the bones.
When the film is developed, the parts exposed to xrays are lighter than the surrounding tissue so the
bones appear lighter.
Too much exposure xrays can cause the same damage as gamma rays. People who work with
xrays must wear a film badge. If the badge is overexposed, its wearer cannot continue working