# KS4 Waves : Dispersion and Electromagnetic radiation

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KS4 Waves : Dispersion and Electromagnetic radiation

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After this presentation you will be able to:
Define dispersion. Describe how different colours are refracted different amounts. List the order of radiations in the electromagnetic spectrum. Recall the uses and dangers of the radiations in the electromagnetic spectrum. Describe how radio waves are reflected and diffracted. Recall the effect of EM radiation on living tissue. Describe how X ray images are formed. Describe the effects of incident EM radiation on materials. Recall the different absorption of EM radiation by different coloured skin. Explain how microwaves can heat up foods containing water. Describe how infrared radiation can be used to form ‘heat images’.

Dispersion Experiment
1. Connect a ray box to a power source. The ray box will get very hot. Take care!!!!! 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.

Explaining dispersion
The different colours of light have different wavelengths. Different wavelengths are refracted different amounts. The white light ray is split into a spectrum of colours. This is known as DISPERSION. 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.

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

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 animation.

Electromagnetic Spectrum
Although all e-m 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 e-m waves depends on the wavelength [].

Wavelength () increases
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 Low frequency Long wavelength Low energy Least penetrating High frequency Short wavelength High energy Most penetrating

Electromagnetic Spectrum
Flash activity - drag the dark blue boxes to the appropriate grey box so that the spectrum is in the correct order by wavelength.

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

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

EM Radiation: Uses: Dangers:
X rays How do hospital workers limit their exposure to Gamma and X rays? Shadow pictures of luggage and inside the human body. 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. High doses can kill cells. Lower doses can cause cells to become cancerous.

X rays How are X rays 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

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

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, the less can reach into deeper soft tissues.

EM Radiation: Uses: Dangers:
Light Seeing and endoscopes Blindness

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

Which are the hottest/coolest parts of the image shown?
Night vision Which are the hottest/coolest parts of the image shown? 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. light is hot dark is cold

EM Radiation: Uses: Dangers:
Microwaves Satellite communication, mobile phone networks, cooking, RADAR. Internal tissue heating.

Microwaves How do microwaves cook foods?
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

EM Radiation: Uses: Dangers:
Radio waves EM Radiation: Uses: Dangers: Radio waves Communication and astronomy.

Radio waves 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? All electromagnetic radiation travels in straight lines, does it not? Radio waves diffract around the hill to the house. Remember diffraction?

Getting hotter If electromagnetic radiation is incident upon a material what effects could it have? An alternating current could be induced in the material, with the same frequency as the incident radiation. The temperature of the material could increase. 70º C 50º C 30º C 21º C

EM Questions 1) Match up the following parts of the electromagnetic spectrum with their uses : Gamma rays Allow us to see Radio waves Remote Controls Ultra Violet ‘See’ broken bones Visible Carry TV signals Microwaves RADAR X rays Sterilise equipment Infra Red Causes sun-tans

EM Questions 2) Which radiations are missing from below? ___________
Gamma A Ultraviolet Light Infrared B Radio waves ___________ X rays Microwaves

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