P6 Wave Behaviour and Electromagnetic Waves (page 220)

Question 1

When a wave meets a boundry between two materials, what three things can happen?

Answer 1

The wave can be:

Absorbed
Transmitted
or Reflected

Question 2

What is meant by ‘The wave is Absorbed by the second material when a wave meets a boundary’ between two materials?

Answer 2

The wave transfers energy to the material’s energy stores. Often, energy is transferred to the thermal energy strore, which leads to heating (this is how a microwave works (see page 223).

Question 3

What is meant by ‘The wave is Transmitted through the second material when a wave meets a boundary’ between two materials?

Answer 3

the wave carries on travelling through the new material. This often leads to refraction (see page 221). This can be used in communications (p.222) as well as in the lenses of glasses and cameras.

Question 4

What is meant by ‘The wave is Relected’ when a wave meets a boundary between two materials?

Answer 4

The wave is reflected - this is where the incoming ray is neither absorbed or transmitted, but instead is ‘sent back’ away from the second material. This is how echoes are created.

(what actually happens depends on the wavelength of the wave and the properties of the materials involved).

Question 5

Electromagnetic (EM) waves are transverse waves, true or false?

Answer 5

True (see p.218)

Question 6

What do transverse waves mean?

Answer 6

they transfer energy from a source to an absorber.

Question 7

A camp fire transfers energy to its surroundings by emitting infrared radiation, how?

Answer 7

the infrared waves are absorbed by objects and transfer energy to the object’s thermal energy store, causing the object to warm up.

Question 8

Radio waves transfers energy to what what energy store and how?

Answer 8

the kinetic energy stores of electrons in radio receivers, which generates an electric current (see page 222).

Question 9

How do EM waves travel at the same speed?

Answer 9

through air or a vacuum (space).

Question 10

electromagnetic waves aren’t vibrations of particles, so what are they?

Answer 10

they’re vibrations of electric and magnetic fields (p.227). This means they can travel through a vacuum.

Question 11

Electromagnetic waves can travel at different speeds in different materials, which can lead to what?

Answer 11

refraction

Question 12

What is the variation for EM waves?

Answer 12

from around 10-¹⁵ m to more than 10⁴ m

Question 13

How are EM waves grouped?

Answer 13

it is based on their wavelength and frequency

Question 14

how any types of groupes are there for wavelength and frequency?

Answer 14

seven, but the different groups merge to form a continuous specrum.

Question 15

Our eyes can only detect a small part of the wavelength and frequency specturm, through what?

Answer 15

by visible light.

Question 16

Name the seven different groups of wavelengths, and their frequency?

(a handy mnemonic for this order of EM waves is: ‘Rock Music Is Very Useful for eXperiments with Goats’

Answer 16

Radio Waves 1m - 10⁴ m
Micro Waves 10-² m
Infra Red 10-⁵ m
Visible Light 10-⁷ m
Ultra violet 10-⁸ m
X-Rays 10-¹⁰ m
Gamma Rays 10-¹⁵ m

See diagram on page 230.

Question 17

If long wavelength means low frequency, what do short wavelength mean?

Answer 17

high frequency.

Question 18

Why is there such a large range of frequencies?

Answer 18

because EM waves are generated by a variety of changes in atoms and their nuclei (p.195).

e.g. changes in the nucleus of an atom creates gamma rays (p.196).

This also explains why atoms can absorb a range of frequencies - each one causes a different change.

Question 19

Becauseof their different properties, different EM waves are used for what?

Answer 19

different purposes.

Question 20

State the type of electromagnetic wave that has the lowest frequency (1 mark)

Answer 20

Radio Waves (1 mark)

Question 21

Name the section of the electromagnetic spectrum that humans can see (1 mark)

Answer 21

Visible light spectrum (1 mark).