Topic 2 - Waves and EM Spectrum

Question 1

what is a wave?

Answer 1

an oscillation that transfers energy without transferring any matter

Question 2

transverse waves

Answer 2

oscillations are perpendicular to the direction of energy transfer
- they DON’T need a medium to travel through

Question 3

examples of transverse waves

Answer 3

EM waves, ripples on water

Question 4

longitudinal waves

Answer 4

oscillations are parallel to the direction of energy transfer
– they DO need a medium to travel through

Question 5

examples of longitudinal waves

Answer 5

sound waves

Question 6

amplitude

Answer 6

distance from the undisturbed position to the peak or trough
( maximum displacement )

Question 7

wavelength

Answer 7

distance between the same point on two adjacent waves

Question 8

frequency

Answer 8

number of waves passing a point per second (Hz)

Question 9

period

Answer 9

amount of time it takes for a wave to pass a point (s)

period = 1 / frequency

Question 10

wave speed

Answer 10

speed = wavelength x frequency

Question 11

speed of sound in air

Answer 11

340 m/s

Question 12

what 3 things can happen to a wave once it enters a different medium?

Answer 12

1) absorption
2) reflection
3) transmission ( refraction )

Question 13

absorption

Answer 13

waves are absorbed by the material and energy is transferred to the material’s energy stores

Question 14

reflection

Answer 14

the waves may bounce back

Question 15

transmission

Answer 15

the waves keep on travelling through the new material but often undergo refraction

Question 16

refraction

Answer 16

• when the speed of a wave changes as it crosses a boundary so
• changes direction if it hits the boundary at an angle ( not normal )

Question 17

speed of waves in refraction

Answer 17

if it bends towards the normal it is moving slower
if it bends away from the normal it is moving faster

Question 18

interpreting wavefronts

Answer 18

when the wavelength of the waves decreases it shows that the wave is moving more slowly, and so bending towards from the normal

Question 19

how do sound waves travel?

Answer 19

• the particles vibrate from side to side
  -parallel to the direction of wave travel
• vibrations passing through the object passing on the energy

Question 20

why does sound travel fastest in solids?

Answer 20

• solid is more dense so the particles are more closely packed together
• frequency of vibrations between particles will increase and so wave will travel faster through the material

Question 21

what stays the same and what changes when a wave is refracted

Answer 21

frequency remains constant
wavelength changes

Question 22

auditory range

Answer 22

20 Hz - 20kHz

Question 23

how do ears detect sound? (P1)

Answer 23

• sound wave travel through ear canal
• causing eardrums to vibraet
• ossicles transmit these vibrations to the cochlea

Question 24

how do ears detect sound? (P2)

Answer 24

• cochlea converts these into electrical signals
• passing through the auditory nerve into the brain where they are interpreted as sound

Question 25

what is ultrasound?

Answer 25

sound waves with frequency above 20kHZ. they are partially reflected

Question 26

industrial imaging - Ultrasound use

Answer 26

• used in industry to make sure objects aren’t faulty
• normally ultrasound waves will be refracted by the far end of object but
• if there is a crack then the ultrasound wave will be partially reflected and detected sooner

Question 27

echo sounding

Answer 27

• used to find depth of water or locate submarine
• a pulse of ultrasound waves emitted and time taken for echo to return is noted
  -helps us find depth of water

Question 28

EM Waves

Answer 28

• group of transverse waves that transfer energy from source to absorber

Question 29

order of EM waves ( increasing freq)

Answer 29

radio, microwave, infrared, visible light, UV, X-ray, gamma ray

Question 30

uses of radio waves `

Answer 30

communication : radio and bluetooth

Question 31

uses of microwaves `

Answer 31

satelite communication, cooking food

Question 32

use of infrared

Answer 32

infrared cameras, cooking , electric heaters

Question 33

use of visible light

Answer 33

vision, fibre optic cables

Question 34

use of UV

Answer 34

sun tanning , energy efficient lamps

Question 35

use of X-ray

Answer 35

visualise broken bones

Question 36

use of gamma ray

Answer 36

sterilising medical objects
radiotherapy

Question 37

dangers of UV, X-ray and Gamma

Answer 37

they are all high frequency which means they carry lot of energy and can cause damage to cells

Question 38

dangers of UV

Answer 38

damages skin and causes sunburns
can cause skin cancer

Question 39

dangers of X-rays and gamma rays

Answer 39

ionising radiation
ability to knock electrons off atoms
destroys cells and causes gene mutation
leads to cancer

Question 40

seismic waves

Answer 40

produced by earthquakes and carry energy away from earthquakes’s epicenter

Question 41

seismic P

Answer 41

longitudinal
pass through solids and liquids

Question 42

seismic S

Answer 42

transverse
only pass through solid

Question 43

using seismic S waves to investigate earth’s structure

Answer 43

can’t detect S waves on other side of earth because some of earth’s structure is a liquid ( core )

Question 44

using seismic P waves to investigate earth’s structure