Electromagnetic waves (paper 2)

What 2 things do all electromagnetic waves have in common?

1. They are all transverse waves that transfer energy from a source to an absorber

2. All EM waves travel at the speed of light through air or a vacuum (space)

What’s the continuous spectrum of EM waves?

Waves have a range of frequencies they are ordered based on their frequency and wavelength

What happens to the frequency as you go up the continuous spectrum and why?

it increases due to having more energy

What happens to the wavelength as you go up the continuous spectrum?

wavelength decreases (gets shorter)

What is the order of the continuous spectrum?

Radio waves

Microwaves

Infrared

Visible light

Ultra violet

X-rays

Gamma rays

what do Radio waves do and how are they made?

• Transfer energy

• made by oscillating charges

What happen when charges oscillate?

• They produce oscillating electric and magnetic fields (electromagnetic waves)

• frequency of waves will be equal to the frequency of the alternating current

What’s the object where electrons oscillate to create radio waves?

A transmitter

What happens when radio waves reach a receiver?

• They are absorbed

• Energy is transferred to the electrons in the material

• Causes electrons to oscillate

What are radio waves used for?

Mainly communication eg, FM (frequency modulation) radio, Tv, Bluetooth

Why are radio waves used for communication?

• They have the longest wave length

• Long wave lengths diffract (bend) around curved surfaces of the Earth, they can diffract over hills, into tunnels

• Makes it possible for radio waves to be received even if receiver isn’t in a line of sight of the transmitter

Why can radio waves be received over long distances from transmitter?

They are reflected off of the ionosphere

What is the ionosphere?

An electrically charged layer in the Earth’s upper atmosphere

What’s FM transmissions?

• frequency modulation

• Have short wavelengths

• Must be in direct sight of transmitter, signal doesn’t bend or travel through buildings

What are microwaves used for?

• satellites

• Microwave ovens

How are microwaves used in satellites?

• microwaves can pass easily through the Earth’s watery atmosphere

• Signal from transmitter is transmitted into space

• Satellite receiver dish picks it up, whilst orbiting thousands of km above Earth, it transmits signal back to Earth in a different direction

• Received by a satellite dish on the ground, there’s a time delay between transmitter and receiver due to the long distance

How do microwave ovens use microwaves?

• microwaves are absorbed by water molecules in food

• water molecules transfer energy to the rest of the molecules in the food by heating, this quickly cooks the food

What is Infrared radiation used for?

• increase temperature

• Monitor temperature

• Eg. infrared camera, electric heaters, foods can be cooked

What gives off infrared radiation?

• hot objects

• The hotter the object, the more IR radiation is given out

How are infrared cameras used?

• used to detect and monitor IR radiation

• Turns it into an electrical signal, that’s displayed on a screen as a picture, hotter the object, the brighter it appears

Cooking food using IR radiation

absorbing IR causes objects to get hotter

IR radiation in electric heaters

• contain long piece of wire, heats up as current flows through

• Wire emits lots of IR radiation (and visible light, glows)

• Emitted IR radiation is absorbed by objects and air in the room

• Energy is transferred by IR waves to thermal energy stores of the objects, causing temperature to increase

What is visible light?

• Light we can see

• It’s made up of a range of colours

What’s visible light used for?

• photography

• Illumination

What’s the visible light spectrum?

• A range of wavelengths that we perceive as different colours

• Each colour has its own narrow range of wavelengths and frequencies

• Colours can mix together to make other colours (can’t mix primary colours)

Order of the visible light spectrum

RED

ORANGE

YELLOW

\
GREEN

\
BLUE

INDIGO

VIOLET

What do colours of objects depend on?

Which ever wavelength of light are most strongly reflected

What’s fluorescence?

• a property of certain chemicals

• UV radiation is absorbed, visible light is emitted (giving you brightness)

• Can be used to identify forged bank notes

What can UV radiation be used for?

• security pens

• Suntans

How do security pens work?

• under UV light the ink will glow (fluorescent)

• Invisible without UV light

• Can help police identify property if stolen

What’s UV light produced by?

The sun

How is UV light dangerous?

• tanning salons use UV lamps to give artificial suntan

• They have hazardous properties (used to kill bacteria)

What are x-rays and gamma rays used for?

Medicine

How can x-rays be used

• too look/identify broken bones

• Tests for cancer (along with hammer rays)

Why are x-rays used to look/identify broken bones?

• they can easily pass through flesh

• Can’t pass through denser material (bones, or metal)

What gives you a x-ray?

The amount of radiation absorbed

how are gamma and x-rays used to kill cancer cells?

High doses kill all living cells, they are directed towards cancer cells, to avoid killing too many healthy cells

what are the jobs of radiographers

to use x-rays and gamma rays that treat people with cancer

What are radiographers?

people who work with x-rays and radiotherapy

What do radiographers use to protect them against rays?

• wear lead aprons

• Stand behind a lead screen

• Leave the room

How can EM radiation be harmful to people?

High frequency waves (UV, X-ray, gamma) transfer lots of energy, causing damage to tissues

How is UV radiation dangerous?

• can damage surface cells (sunburn)

• Cause skin to age prematurely

• Blindness or increase risk of skin cancer

How are x-rays and gamma rays dangerous?

• they are types of ionising radiation

• Can cause gene mutation (cancer)

• Can lead to secondary cancer

How much likely are you to suffer damage to skin cells if you were to have a CT scan?

4 times more likely

Why are infrared cameras able to show parts of the hand at different temperatures?

Different temperatures emit different intensities of infrared, which are represented as different shades/colours on the camera