waves

Question 1

what do waves do?

Answer 1

they transfer energy from one place to another but not matter

Question 2

what are transverse waves?

Answer 2

waves whose oscillations are perpendicular to the direction of the wave

Question 3

what are examples of transverse waves?

Answer 3

• electromagnetic waves
• ripples on water
• waves on a string

Question 4

what are longitudinal waves?

Answer 4

waves whose oscillations are parallel to the direction of the wave

Question 5

what are examples of longitudinal waves?

Answer 5

• sound waves

- seismic waves

Question 6

what is frequency?

Answer 6

number of waves passing a point each second

Question 7

what is a period?

Answer 7

the time for one complete wave

Question 8

what is the equation for a period?

Answer 8

T = 1/f

Question 9

what is the speed of light?

Answer 9

3 × 10⁸ m/s

Question 10

what can happen when waves arrive at a boundary between two different materials?

Answer 10

• absorption
• reflection
• transmission (refraction)

Question 11

what is the rule for all reflected waves?

Answer 11

the angle of incidence = angle of reflection

Question 12

when does specular reflection occur?

Answer 12

when waves are reflected in a single direction and the boundary is smooth

Question 13

when does diffuse reflection occur?

Answer 13

when waves reflected in multiple directions and the boundary is rough

Question 14

what occurs during refraction?

Answer 14

a wave crosses a boundary and changes direction

Question 15

what affects the speed of a wave passing through a material?

Answer 15

the material’s density

Question 16

when does a wave bend towards the normal when passing through a material?

Answer 16

when the material has a higher density and the wave slows down

Question 17

when does a wave bend away from the normal when passing through a material?

Answer 17

when the material has a lower density and the wave speeds up

Question 18

what happens to the wavelength if a wave slows down?

Answer 18

it will decrease

Question 19

what are sound waves?

Answer 19

longitudinal waves which cause particles to vibrate parallel to the direction of wave travel

Question 20

how do we hear sound?

Answer 20

• ear canal
• eardrum
• three small bones transmit vibrations to the cochlea

Question 21

what is the frequency of a sound wave related to?

Answer 21

pitch

Question 22

what is the amplitude of a sound wave related to?

Answer 22

volume

Question 23

what is the human hearing range?

Answer 23

20 - 20,000Hz

Question 24

what are ultrasounds?

Answer 24

sound waves which have a frequency above 20,000Hz

Question 25

what happens when ultrasound waves meet the boundary between two different materials?

Answer 25

• some are reflected
• the time taken for the waves to leave and return is measured
• the depth can be determined using the speed of sound and time taken

Question 26

what are ultrasounds used for?

Answer 26

medical and industrial imaging

Question 27

what are seismic waves?

Answer 27

vibrations produced by earthquakes in the earth’s crust

Question 28

what are the types of seismic waves?

Answer 28

primary and secondary waves

Question 29

what are the properties of p-waves?

Answer 29

• longitudinal
• faster
• can travel through solids and liquids

Question 30

what are the properties of p-waves?

Answer 30

• longitudinal
• faster
• can travel through solids and liquids

Question 31

what are the properties of s-waves?

Answer 31

• transverse
• slower
• can only travel through solids

Question 32

what are seismic waves used for?

Answer 32

investigating the earth’s interior structure

Question 33

what do s-waves suggest about the earth?

Answer 33

the outer core must be liquid as it cannot be detected on the opposite side of the earth

Question 34

what do p-waves suggest about the earth?

Answer 34

there is a solid inner core as there are two shadow zones where none can be detected

Question 35

what do all electromagnetic waves do?

Answer 35

• transfer energy as radiation from the source of the waves to an absorber
• travel through a vacuum
• travel at the same speed

Question 36

When are A-scans used?

Answer 36

when the anatomy is known and the distance/depth measurements are needed

Question 37

How does B-scans work in foetal scanning?

Answer 37

Gel is applied to the skin prior to the scan. The transducer array is moved over the skin of the patient about to view the body from a range of angles. Many pulses are sent into the body and partially reflected and partially transmitted at each boundary

Question 38

Advantages of ultrasound to X-rays

Answer 38

• quite cheap, portable and do not need a specialist room
• good for imaging organs and soft tissues
  (non-ionising. low intensities so no known hazards)

Question 39

Disadvantages of ultrasound to X-rays

Answer 39

do not penetrate bone so cannot detect fractures or image the brain
resolution is poor so the scans cannot reveal fine detail
(Sonographer need to be skilled at operating the probe to get a good image)

Question 40

Why does the amplitude of the traces decrease when there is an air gap in the metal block?

Answer 40

Some of the sound is reflected at the crack, so less sound is reflected at the far edge of the metal

Question 41

Waves earthquakes generate are….

Answer 41

seismic waves

Question 42

Why is it important to have seismometer stations at many locations all over the Earth?

Answer 42

We cannot predict when earthquakes occur and early detection allow warnings to be issued

Question 43

How is the size of the core measured?

Answer 43

measuring shadow zones from sudden refraction as a wave travels from one layer to another

Question 44

How is the density of the materials revealed?

Answer 44

The speed and trajectory of the waves