P13 - Electromagnetic Spectrum

Question 1

What are electromagnetic waves?

Answer 1

Electromagnetic waves are a group of transverse waves. They are sometimes called electromagnetic radiation. They consist of vibrating electric and magnetic fields, which is why they can travel through a vacuum - don’t rely on vibrating matter.

Question 2

What is the spectrum?

Answer 2

The spectrum means there are different parts/types or electromagnetic waves. All waves in this spectrum have the same speed/velocity.

Question 3

Smallest wavelengths to longest wavelengths on the spectrum

Answer 3

Gamma X-ray Ultraviolet Visible Light
Infra red Microwaves Radio waves

Question 4

Shortest wavelength to longest wavelength of visible colour

Answer 4

Violet Indigo Blue Green Yellow Orange Red (red is the last colour you can see before it is infra red)

Question 5

What is infrared radiation?

Answer 5

Infrared radiation is absorbed by your skin. It can damage, burn or kill skin cells because it heats up the cells.

Question 6

What can infrared radiation be used for?

Answer 6

Keeping premature babies warm
Used on farms for chicks

Question 7

Infrared Devices

Answer 7

Optical fibres used in communications systems and medical procedures usually use infrared radiation instead of visible light. This is because infrared radiation is absorbed less than visible light in glass fibres. IR has a wide range of different wavelengths.

Question 8

What are optical fibres?

Answer 8

A glass or plastic pipe through which IR wavelengths are transmitted.

Question 9

Properties of microwaves

Answer 9

Longer wavelength than infrared
More dangerous than IR
Less warm than infrared
Water molecules in food absorb microwave - more kinetic energy, more thermal energy
More hydrated food - more effective heating
Shorter wavelength than radio waves
Microwaves can penetrate the atmosphere, therefore used for satellite TV
Also carry mobile phone signals
Microwave ovens heat food faster than normal ovens because microwaves can penetrate into food and are absorbed by water. Normal ovens don’t absorb microwaves.

Question 10

Properties of radio waves

Answer 10

Range from 300,000 Hz to 3000 million Hz
Radio waves are used to carry radio, TV and mobile phone signals
You can use radio waves to connect a computer to other devices such as a printer/computer mouse
Radio waves can be hazardous - penetrate peoples bodies and heat internal parts
Phones transmit/receive radio waves
E.g. Bluetooth (a radio wave) enabled devices can communicate over 10 metres without the need for cables (waves sent out and received)

Question 11

Transmitting radio waves - Steps in diagram

Answer 11

1. Oscillator supplies carrier waves to the transmitter in an alternating current (repeatedly reversing direction when electrons move back and forward).
2. Audio signal is interpreted by the transmitter and modulates carrier waves .
3. Modulated carrier waves from the transmitter are supplied to the Ariel. This emits radio waves carrying audio signal due to alternating current.
4. Radio waves are absorbed by a receiver Ariel inducing alternating current in the receiver Ariel and causing oscilllations.
5. The frequency of the oscillations in the receiver is the same as the frequency of the radio waves.
6. Receiver circuit separates audio signal from the carrier waves. Audio signal is supplied to a loudspeaker which send out sound waves similar to the sound waves received by the microphone in the radio station.

Question 12

Absorption and emission of infrared radiation

Answer 12

Black absorbs more heat than white
White reflects light
Black is a good absorber and a good emmitter of heat

Question 13

Ultraviolet light properties

Answer 13

Used for security marking - bank notes and property, etc
Can also be used for sterilisation
Can go through clouds - causes skin cancer

Question 14

Radio stations

Answer 14

FM only has a 30 mile range
AM - 150 mile range - long wave, further distance but signal quality is worse when long wave frequency

Question 15

What are x-rays?

Answer 15

When electrons are released by electrical supply, which hits an object and produces X-rays.
Can’t go through metal (bone)
Can pass through soft tissues
More high energy/powerful than UV
Radio therapy - X-rays can treat cancer
Can’t have X-rays when pregnant
If doctors are exposed to X-rays, a safety badge tells you how much ionising radiation you have received (if you have been exposed) if so, can’t use X-rays as it could be dangerous
Can also be used for checking materials (find cracks where X-rays leak through)

Question 16

How are X-rays produced?

Answer 16

When electrons or other particles moving at high speed are stopped - X-ray tubes used to produce X-rays

Question 17

What is gamma radiation?

Answer 17

When radioactive element decay, gamma rays are emitted in electromagnetic waves. Very dangerous.