# Physics GCSE P1B

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• Created on: 16-05-11 10:45

• On the move - Short radio waves from a satellite to GPS (TomTom)
• Fixing a fracture - X-rays  to show doctors what is needed
• Hubble Space telescope - For almost 20 years this has been orbiting the earth - pictures sent back by radio waves
• Mobile Phone - Mobile phone masts
• The Sun is a star - this makes its own light
• The Earth is a planet - light is reflected from sun
• The Moon is a satellite - light is reflected from sun

The VISIBLE light spectrum ROYGBIV - light that has all colours - known as white light

White light  is reflected by a mirror

Light  travels in straight lines

The Electro-magnetic Spectrum

Electro-magnetic waves  are electric and magnetic disturbances that transfer energy from one place to another

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One wavelength  is the distance from peak to peak

Frequency = Number of complete waves passing a point each second

The unit of frequency = Hertz

• (Hz) - 1 Hertz = 1 waves per second
• (KHz) - 1 Kilohertz = 1000 waves per second
• (MHz) - 1 Megahertz = 1 million waves per second

EQUATION -

Wavespeed (metres per second) = Frequency (Hz) * Wavelength (metres)

so

Wavelength =       Wavespeed

Frequency

and

Frequency =               Wavespeed

Wavelength

All waves travel at a speed of 300 million metres per second  through space or a through a vacuum

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Remember the order of the Electro-magnetic spectrum - Shortest to Longest

• Gamma Rays
• X-rays
• Ultra Violet
• Visible Light
• Infra-red
• Microwaves

GAMMA RAYS AND X-RAYS

• X-rays and Gamma Rays  radiation are absorbed by dense materials in bone and in metal
• X-rays and Gamma Rays radiation damages living tissue when they pass through it
• X-rays  are used in hospital to take radiographs - they pass through the soft tissue but are absorbed by the bone and thick metal plates
• Gamma Rays are used to:-
• kill harmful bacteria in food
• sterilise surgical equipment
• kill cancer cells

Remember how Gamma Rays are used to cure cancer -

• Cobalt 60 source for the Gamma rays
• Rays leave chamber through exit channel
• Rays are directed to the the cancerous Tumour from a number of directions

• Ultraviolet radiation is in the electro-magnetic spectrum between visible light and Xrays
• Ultraviolet radiation has a shorter wavelength than light
• Ultraviolet  radiation is harmful to the skin and the eyes

****** look at the diagram on page 82 in AQA text book ******

UV is harmful to the skin and the eyes because:-

• Wavelengths are shorter than light
• UV carries more energy than light waves
• too much UV causes sunburn and can cause cancer

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How Electro-magnetic waves react with substances

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Reflected waves :-

• Some or all waves may be reflected

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