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# Dispersion and Electromagnetic Radiation

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Dispersion and Electromagnetic Radiation
KS4 Physics Dispersion and Electromagnetic Radiation

Dispersion and Electromagnetic Radiation
Contents Dispersion and Electromagnetic Radiation Explaining dispersion The electromagnetic spectrum Uses and dangers of EM radiation Summary activities

Dispersion experiment
1. Connect a ray box to a power source. 2. Place a prism on a piece of plain paper. 3. Draw around the prism. 4. Shine a ray of light at the prism. 5. Draw in rays of light to show your observations. Take care! The ray box will get very hot.

Explaining dispersion
The white light ray is split into a spectrum of colours. This is known as dispersion. The different colours of light have different wavelengths. Different wavelengths are refracted different amounts. How do you remember the order of the colours? Richard Of York Gave Battle In Vain Which colour is refracted the most? Red light is refracted least. Violet light is refracted the most.

Refracted more/less by glass
Dispersion summary Red/violet Refracted more/less by glass Longer/shorter wavelength Red/violet Refracted more/less by glass Longer/shorter wavelength

Dispersion and Electromagnetic Radiation
Contents Dispersion and Electromagnetic Radiation Explaining dispersion The electromagnetic spectrum Uses and dangers of EM radiation Summary activities

The electromagnetic spectrum
Light, a type of radiation, is part of the electromagnetic spectrum. The electromagnetic spectrum is made up of different types of radiation. The different types of radiation have different properties and behaviour. All electromagnetic waves can travel through space. All electromagnetic waves travel at the same speed in a vacuum (300,000,000 m/s). TRUE/FALSE

Colour, wavelength and amplitude
We can see the relationship between colour, wavelength and amplitude using this activity.

Electromagnetic spectrum
Although all EM waves travel at the same speed, their wavelength () and frequency (ƒ) can be different. Waves that cook food. Waves that cause sun-tans. The properties, dangers and uses of EM waves depends on the wavelength ().

Electromagnetic spectrum
Radio Micro Infra-Red Light Ultra-Violet X rays Gamma Electromagnetic spectrum Wavelength () increases Gate X Usually Lets In Most Radiation Can you think of a phrase that would help you remember this order? High frequency Short wavelength High energy Most penetrating Low frequency Long wavelength Low energy Least penetrating

Electromagnetic spectrum
Drag the dark blue boxes to the appropriate grey box so that the spectrum is in the correct order by wavelength.

Dispersion and Electromagnetic Radiation
Contents Dispersion and Electromagnetic Radiation Explaining dispersion The electromagnetic spectrum Uses and dangers of EM radiation Summary activities

Uses and dangers of EM radiation
Research the uses and dangers of the various radiations: Radiation Uses Dangers Gamma X-rays Ultraviolet Light Infra red Microwaves Radio waves

Gamma radiation EM radiation: Uses: Dangers: Gamma
Killing harmful bacteria in food, sterilizing surgical equipment, killing cancer cells. Dangers: High doses can kill cells. Lower doses can cause cells to become cancerous.

X-ray radiation EM radiation: Uses: Dangers: X-rays
Shadow pictures of luggage and inside the human body. Dangers: High doses can kill cells. Lower doses can cause cells to become cancerous. Hospital workers limit exposure to gamma and X-rays by standing behind lead shields or by leaving the room when the radiations are being used.

How are X-ray slides formed?
X-rays can penetrate soft tissue but not b_____. X-rays are a_________ more by some materials than others. P____________ f____ is used to detect X-rays. one bsorbed hotographic ilm

Ultraviolet radiation
EM radiation: Ultraviolet Uses: Sun beds, fluorescent lamps and security marking. Dangers: High doses can kill cells. Lower doses can cause cells to become cancerous. The higher the frequency of the radiation, the more dangerous it is. Therefore, gamma is more dangerous than X-rays or ultraviolet.

Effects of EM radiation on living cells
Ultraviolet radiation can pass through skin to deeper tissues. What effect do you think the colour of the skin has on the amount of radiation that passes through it? Infra red radiation is used in toasters, grills and radiant heaters. What effect do you think it has on your skin? The darker the skin, the more ultraviolet radiation is absorbed, and the less can reach into deeper soft tissues.

Light EM radiation: Uses: Dangers: Light Seeing, endoscopes.
Blindness.

Infrared radiation EM radiation: Uses: Dangers: Infrared
Remote controls (TV/VCR), radiant heaters, grills, optical fibre communication, night vision. Dangers: Skin burns

Which are the hottest/coolest parts of the image shown?
Night vision All objects above absolute zero emit infrared radiation. The hotter an object is, the more heat radiation it emits. Some animals and cameras can detect infrared radiation and are able to build up a heat picture. Which are the hottest/coolest parts of the image shown? light is hot dark is cold

Microwave radiation EM radiation: Uses: Dangers: Microwaves
Satellite communication, mobile phone networks, cooking, radar. Dangers: Internal tissue heating

How do microwaves cook food?
Microwaves can be used in c because many foods contain w molecules. Microwaves of the right w are able to make the water molecules r This causes the food to get h ooking ater avelength esonate otter

Radio waves EM radiation: Uses: Radio waves
Communication and astronomy. How do radio signals from the UK reach around the globe? The longer wavelength radio waves from a transmitter reflect off the Earth’s outer atmosphere (ionosphere).

Radio waves How can houses in the shadows of hills receive a radio signal? Remember diffraction? All electromagnetic radiation travels in straight lines. Radio waves diffract around the hill to the house.

Dispersion and Electromagnetic Radiation
Contents Dispersion and Electromagnetic Radiation Explaining dispersion The Electromagnetic Spectrum Uses and dangers of EM radiation Summary activities

Glossary (1) dispersion – The splitting of light ray light into the range of colours that make up that light, e.g. when white light is split into the colours of the rainbow. electromagnetic spectrum – The complete range of electromagnetic waves that have different wavelengths (and frequencies). gamma rays – Electromagnetic waves with very short wavelengths, and which are given off by radioactive materials. infrared – Electromagnetic waves given off by hot objects, like grills and radiators, and used by TV remote controls. light – Electromagnetic waves that are detected by the eye.

Glossary (2) microwaves – Electromagnetic waves used for satellite communication, radar, mobile phone networks and cooking. prism – A triangular block of glass or plastic. radio waves – Electromagnetic waves with very long wavelengths, which are used to transmit radio and TV signals. spectrum – The range of all the colours of the rainbow that make up white light: red, orange, yellow, green, blue, indigo, violet. ultraviolet – Electromagnetic waves that are present in sunlight and cause some types of skin to darken. They also cause chemicals to glow in fluorescent lamps. X-rays – Electromagnetic waves with short wavelengths that are used for producing images of the inside of the body.

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