P13 Electromagnetic Waves

Question 1

What are electromagnetic waves?

Answer 1

Transverse waves that transfer energy from the source of the waves to an absorber

They form a continuous spectrum and all electromagnetic waves travel at the same velocity through a vacuum or air

Question 2

What is the order of the electromagnetic spectrum based on?

Answer 2

The electromagnetic spectrum goes from long wave length and low frequecny to short wavelength and high frequency

Question 3

Why can we only see a limited range of electromagnetic waves?

Answer 3

Because our eyes only detect invisible light

Question 4

Examples of energy transferred by electromagnetic waves

Answer 4

Microwave ovens - energy transferred from microwave source to the food in the oven heating it

Radiant heaters - Infrared radiation transfers energy from the heater to heat the surroundings

Question 5

Equation for speed of electromagnetic waves?

Answer 5

Wave speed = frequency x wavelength

Question 6

How are radio waves produced?

Answer 6

Radio waves can be produced by oscillations in electrical circuits

Question 7

What happens when radio waves are absorbed?

Answer 7

When radio waves are absorbed, they may induce oscillations in a complete electrical circuit therefore creating an alternating current with the same frequency as the radio wave itself,

Question 8

How also can electromagnetic waves be generated?

Answer 8

Changes on atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range

E.g. gamma rays originate from changes in the nucleus of an atom

Question 9

What is radiation dose?

Name the electromagnetic waves that can have a harmful effect on human tissue?

Answer 9

A measure of the risk of harm resulting from an exposure of the body to radiation

Ultraviolet waves, x-rays and gamma rays have hazardous effects of human body tissue

Question 10

What do ultraviolet waves do to skin

Answer 10

Cause it to age prematurely and increase the risk of skin cancer

Question 11

Give electromagnetic waves that are ionising radiation

Answer 11

X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer

Question 12

Give explanation why radio waves are suitable for television and radio?

Answer 12

• Radio waves have long wavelengths
• Long wavelengths can diffract around the curved surface of the earth
• This makes it possible for radio signals to be received even ic the receiver isn’t in the line of sight of the transmitter

Question 13

Give explanation why mirco waves are suitable for sattellite communications, cooking food ?

Answer 13

For comms satellites :
-Microwaves can pass easily through earth’s watery atmosphere

For cooking food :
- Use different wave length radio waves in order to penetrate into water molecules and then become absorbed to transfer energy by heating

Question 14

Give explanation why infrared waves are suitable for electrical heaters, cooking food, infrared cameras?

Answer 14

• Infrared waves given out by all hot objects. The more radiation given out the hotter it is. So infrared cameras used to tell how hot an object is
• Electric heaters. Wire heats up and emits IR radiation because it is hot.
• This energy is transferred by IR waves to thermal energy stores of objects in the room
• Therefore heating the room up
• Same principal with food cooking it

Question 15

Give explanation why Visible light waves are suitable for use in fibre optic communications?

Answer 15

• Light waves are easily reflected

- Light waves are bounced back and forth inside the wire before they reach the end of the wire

Question 16

Give explanation why Ultraviolet radiation used in sun tanning?

Answer 16

• Exposure to UV light gives you a suntan

Question 17

Give explanation why X-rays and gamma rays used in medical imaging?

Answer 17

• X-rays lass easily through flesh but not so easily through bones
• They amount of radiation absorbed (or not) gives you the x-ray image

-Gamma rays can be used as a medical tracer

Question 18

Name the 7 types of electromagnetic waves in order from lowest frequency to highest frequency

Answer 18

Radio waves
Microwaves
Infrared Waves 
Visible light 
Ultraviolet
X-rays
Gamma rays