Wave behaviour

Question 1

What does the behaviour of EM waves in different materials depend on?

Answer 1

wavelength and velocity

Question 2

What are EM waves composed of?

Answer 2

an electric field and a magnetic field at right angles

Question 3

speed of EM waves in a vacuum/air

Answer 3

3 x 10[8] m/s

Question 4

What four things can happen to EM waves?

Answer 4

1) reflected off a surface
2) refracted when they move from one material to another
3) transmitted when they pass through a material

4) absorbed by different material
(for example, UV is absorbed by the skin but not by the atmosphere)

the extent that these happen depends on material and wavelength of the EM waves

Question 5

uses of radio waves and microwaves

Answer 5

they are both used for communicating, they can transmit signals for TV, radio etc.

Question 6

What properties make radio and microwaves ideal for communication?

Answer 6

they are easily transmitted through air

do not cause damage if absorbed by the human body

can be reflected to change their direction

Question 7

How are radio/microwaves transmitted?

Answer 7

• radio waves are produced by oscillations in electrical circuits
• they are absorbed by a conductor, and create an alternating current
• the current has the same frequency as the radio waves
• information is coded into the wave before transmission, so it can be decoded when the wave is recieved
• the current is sent up a transmitting aerial, and waves are released

Question 8

How do radio waves travel to another aerial?

Answer 8

• radio waves travel/reflect off the Earth
• radio waves are refracted and then reflected by the ionosphere (upper atmosphere)
• microwaves are transmitted by the ionosphere and re-transmitted by a communication satellite
• they are then recieved by a recieving aerial

Question 9

ionosphere

Answer 9

upper atmosphere

Question 10

How are transmitted radio waves interpreted?

Answer 10

• the wave can be transferred into an alternating current using the oscillations and an electrical circuit
• the alternating current can be decoded

Question 11

What are wave velocities influenced by?

Answer 11

the density of the material

Question 12

How do microwaves heat up food?

Answer 12

high frequency microwaves are easily absorbed by molecules in food

the internal energy of the molecules increases when they absorb microwaves, which causes heating

Question 13

internal energy

Answer 13

The total kinetic energy and potential energy of the particles in an object.

Question 14

infared and heating/thermal cameras

Answer 14

infared light has frequencies which are absorbed by some chemical bonds

the internal energy of the bonds increases when they absorb infared light, which causes heating

all objects emit infared light, infared cameras can detect this and allow people to be detected in the dark

Question 15

Explain why it is not possible to get a suntan if you are inside a house, but it is possible to listen to the radio [4]

Answer 15

the ultraviolet rays that cause suntans are not transmitted by the walls of houses, they are absorbed

radio waves are transmitted by the walls so can be detected by a radio receiver inside the house

Question 16

State four things that can happen to EM waves [2]

Answer 16

be reflected, be refracted, be transmitted, be absorbed

Question 17

Explain why we do not need a communication satellite to relay some waves [2]

Answer 17

they are refracted by the ionosphere and reflected back to receivers on the surface of the Earth

Question 18

Why can’t x-rays and gamma rays be used to communicate?

Answer 18

they can’t reach the surface of the Earth as they are absorbed by the upper atmosphere

they are also harmful to humans and animals