© boardworks ltd 2003 ks4 waves : dispersion and electromagnetic radiation

© Boardworks Ltd 2003

KS4 Waves : Dispersion and Electromagnetic

radiation


A slide contains teacher’s notes wherever this icon is displayed -

To access these notes go to ‘Notes Page View’ (PowerPoint 97) or ‘Normal View’ (PowerPoint 2000).

Normal ViewNotes Page View

Teacher’s Notes

Flash Files

A flash file has been embedded into the PowerPoint slide wherever this icon is displayed –

These files are not editable.


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.

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.

The ray box will get very hot.

Take care!!!!!


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.

Red light is refracted least.

Violet light is refracted the most.

Which colour is refracted the most?

How do you remember the order of the colours?Richard Of York Gave Battle In Vain


Dispersion Summary

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

TRUE/FALSE

TRUE/FALSE

TRUE/FALSE

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.

The properties, dangers and uses of e-m waves depends on the wavelength [].

Waves that cook food.

Waves that cause sun-tans.



Radio

Micro

Infra-Re

dLight

Ultra-V

iolet

X rays

Gam

ma

Wavelength () increases

Can you think of a phrase that would help you remember this order? Gate X Usually Lets In Most Radiation

High frequency

Short wavelength

High energy

Most penetrating

High frequency

Short wavelength

High energy

Most penetrating

Low frequency

Long wavelength

Low energy

Least penetrating

Low frequency

Long wavelength

Low energy

Least penetrating


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:

Kills harmful bacteria in food, sterilising surgical equipment, killing cancer cells.

High doses can kill cells. Lower doses can cause cells to become cancerous.

Gamma


EM Radiation:

Uses:

Dangers:

Shadow pictures of luggage and inside the human body.


X rays

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 do hospital workers limit their exposure to Gamma and X rays?


X rays

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.

onebsorbed

hotographicilm

How are X rays slides formed?


EM Radiation:

Uses:

Dangers:

Sun beds, fluorescent lamps and security marking.


UltravioletWhich type of radiation is the most dangerous?

The higher the frequency of the radiation, the more dangerous it is. So gamma is more dangerous than X rays or ultraviolet.


Effects of EM radiation on living cells

Infra red radiation is used in toasters, grills and radiant heaters.

What effect do you think it has on your skin?

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?

The darker the skin, the more ultraviolet radiation is absorbed, the less can reach into deeper soft tissues.


EM Radiation:

Uses:

Dangers:

Seeing and endoscopes

Blindness

Light


EM Radiation:

Uses:

Dangers:

Remote controls (TV/VCR), radiant heaters, grills, optical fibre communication, night vision.

Skin burns

Infrared


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


EM Radiation:

Uses:

Dangers:

Satellite communication, mobile phone networks, cooking, RADAR.

Internal tissue heating.

Microwaves


Microwaves

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____.

How do microwaves cook foods?

ookingater

avelengthesonate

otter


EM Radiation:

Uses:

Dangers:

Communication and astronomy.

Radio waves

Radio waves


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).


How can houses in the shadows of hills receive a radio signal?

All electromagnetic radiation travels in straight lines, does it not?

Remember diffraction?Radio waves diffract around the hill to the house.

Radio waves


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.

21º C30º C50º C70º 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

A. ___________

B. ___________

X rays

Microwaves

© boardworks ltd 2003 ks4 waves : dispersion and electromagnetic radiation

Documents

gamma slide

x rays x rays

penetrating slide

ultraviolet radiation

powerpoint slide

different types of radiation

rays of light

type of radiation