Waves and boundaries

Question 1

boundary or interface

Answer 1

where two materials meet

Question 2

What happens when a sound, water, or light wave reaches the boundary between two materials?

Answer 2

it can be:

• reflected
• refracted
• transmitted
• absorbed

Question 3

wavelength and the effect on substances and radiation

Answer 3

Different substance do different things which vary with wavelength.

different wavelengths of radiation are absorbed by molecules in the atmosphere by different amounts

Question 4

reflection and sound waves

Answer 4

sound is reflected when there is a big difference between the densities of the materials at an interface

the greater the difference in density, the more sound energy will be reflected

Question 5

transmitting and sound waves

Answer 5

sound is transmitted through a material when the densities between the materials are similar

Question 6

transmitted

Answer 6

a wave is passed through or across a material

Question 7

refraction

Answer 7

process by which a wave changes speed and sometimes direction upon entering a denser or less dense material

sound, water and light waves can all be refracted

Question 8

absorbed

Answer 8

energy is taken in by the material and the internal energy of the material will increase

Question 9

reflection

Answer 9

the wave bounces back off the material

Question 10

absorption and sound waves

Answer 10

sound can be absorbed by materials

the amount depends on the material and the wavelength of the sound

Question 11

refraction special case

Answer 11

when a wave moves from one material into another the direction doesn’t change if it moves along the normal

(a wavefront doesn’t travel along the lines but perpendicular to them)

Question 12

sound waves and refraction

Answer 12

sound waves travel slower in cooler, denser air than warmer, less dense air

this results in a change in direction towards the normal when entering denser air

the waves also slow down, the lines on a diagram get further apart

Question 13

What determine where the normal is on a boundary?

Answer 13

perpendicular to the boundary

Question 14

water waves and refraction

Answer 14

water waves travel faster in deep water than in shallow water

this results in a change in direction towards the normal when entering shallower water

the speed also slows down, so the wavefronts get closer together

Question 15

light waves and refraction

Answer 15

light waves can slow down and change direction when they pass from air to glass

when passing from air to glass they get closer towards the normal

the wavefronts get closer together

Question 16

On a ray diagram

a) what are the non-refracted and refracted rays called?
b) which angles are measured?

Answer 16

a) incident ray and refracted ray

b) the angles between the incident/refracted rays and the normal

Question 17

A person blows a dog whistle. The dog is 200m away.

Explain why the dog will hear the whistle faster ona warm day than on a cool day.

Answer 17

air temperature affects the speed of sound

air molecules at a higher temperature have more kinetic energy than air molecules at a lower temperature, so they vibrate faster

since the air molecules vibrate faster, sound waves travel through warm air faster than cooler air

Question 18

State four things that can happen to a wave at the boundary between two materials

Answer 18

they can be:

• reflected
• refracted
• transmitted or
• absorbed

Question 19

Explain the changes that occur to a wave during refraction

Answer 19

speed will change

direction may change unless travelling along the normal

wavelength of the wave will change

Question 20

Suggest how the absorption of infared radiation in the atmosphere is

a) useful
b) a problem

Answer 20

a) stops infared radiation reaching us
could cause overheating/death

b) it stops infared radiation getting to us from space that could help us detect other objects in space

may be useful when it is too cold to keep people or crops warm

may have an impact on studies of the atmosphere or space

Question 21

How does speed affect wavelength?

Answer 21

they are directly proportional

a lower speed means a smaller wavelength

this means that if a wave slows down at a boundary the wavelength also decreases

(wavelength also has a significant impact on the amount of transmission or absorption)