P12 Wave Properties

Question 1

what are mechanical waves
and give examples

Answer 1

waves that travel through a medium
and can be transverse or longitudinal
e.g. sound waves, water waves, seismic waves

Question 2

what are electromagnetic waves
and give examples

Answer 2

waves which travel through a vacuum at 300,000km per second
and are transverse
e.g. light waves, radio waves, microwaves

Question 3

describe the oscillations of transverse waves

Answer 3

perpendicular to the direction of energy transfer

Question 4

describe the oscillations of longitudinal waves

Answer 4

parallel to the direction of energy transfer

Question 5

what is the amplitude of a wave

Answer 5

its maximum displacement from a point of rest

Question 6

the larger the amplitude of a wave…

Answer 6

the larger the amplitude of a wave
the more energy the waves carry

Question 7

what is the frequency of waves
and unit

Answer 7

the number of waves passing over a fixed point every second
Hz

Question 8

what is the period of a wave
and unit

Answer 8

the amount of time it takes for each wave to pass a fixed point
in seconds

Question 9

v = f λ
what unit is wavelength in

Answer 9

λ is in metres

Question 10

how to calculate speed of sound in air

Answer 10

person A stands at a fixed, measured distance from person B,
A bangs cymbals,
using a stopwatch B times the interval between seeing and hearing the impact of the cymbals,
repeat 3x and calculate a mean time interval in seconds,
substitute values into speed (m/s) = distance (m) / time (s)

Question 11

what is the refraction of a wave

Answer 11

the change of a wave’s direction when crossing the boundary between one medium and another

Question 12

when an incident wave is refracted, which of these change:
- wavelength,
- frequency,
- speed.

Answer 12

frequency stays the same

but speed changes
which causes wavelength to change too.

Question 13

whether a wave is reflected by a surface depends on:

Answer 13

• its wavelength,
• the material of the surface.

Question 14

what happens to a substance when it absorbs waves?

Answer 14

it heats up
because gains energy from the waves

Question 15

what happens to the amplitude of a wave as it travels through a substance
and why?

Answer 15

it gradually decreases
because the substance gradually absorbs some of the substance’s energy

Question 16

what happens to waves that pass through a substance but are not absorbed?

Answer 16

they are transmitted

Question 17

describe how humans hear sound
and why human hearing is limited

Answer 17

• sound waves vibrate the ear drum,
• causing the sensation of sound,
• but this only works over a limited frequency range,
• so outside this range humans cannot hear sounds.

Question 18

how does a loudspeaker produce sound waves?

Answer 18

• it pushes surrounding air backwards and forwards,
• producing sound waves.

Question 19

equation for calculating the speed of sound in air

Answer 19

a = 2d/t

Question 20

increased amplitude means that a sound wave sounds…

Answer 20

louder

Question 21

range of normal human hearing

Answer 21

20 Hz to 20 kHz

Question 22

define ‘echo’

Answer 22

the reflection of sound waves from a smooth surface

Question 23

what is echo sounding

Answer 23

using pulses of high frequency sound to detect objects in deep water and measure water depth below a ship

Question 24

describe the process of echo sounding

Answer 24

• transmitter releases pulses of high frequency sound waves,
• which are reflected at the sea bed,
• back up to a receiver at an equal depth to the transmitter,
• s (twice the depth of the seabed) = v (speed of sound in water) x t (time taken for waves to be emitted then reflected back),
• so depth of water = 1/2 s = 1/2vt

Question 25

what is the frequency of ultrasound waves

Answer 25

over 20kHz

Question 26

how do ultrasound waves show how far away a boundary is

Answer 26

• ultrasound waves are partially reflected when they meet a boundary between 2 media,
• the time taken for waves to reach a receiver again can be used to determine how far away the boundary is from it.

Question 27

uses of ultrasound waves

Answer 27

medical imaging
industrial imaging

Question 28

advantages of ultrasound waves rather than X rays for medical imaging

Answer 28

• non-ionising, so harmless,
• reflect at boundaries between different media so can be used to scan organs and soft tissues.

Question 29

2 main types of seismic wave

Answer 29

P (primary) waves
S (secondary) waves

Question 30

compare P and S waves

Answer 30

P waves
- longitudinal seismic waves,
- travel through solids and liquids at different speeds,

S waves
- transverse seismic waves,
- cannot travel through liquids.