waves

Question 1

what does in phase mean?

Answer 1

when 2 objects with the same frequency are at the same stage in their oscillations

Question 2

what does anti phase mean?

Answer 2

180 degrees out of phase

Question 3

what is phase difference?

Answer 3

if 2 objects are oscillating with the same frequency and are not in phase, the phase difference measures how far out of phase they are

Question 4

what is path difference?

Answer 4

the difference in distances travelled by 2 waves

Question 5

what is a wave?

Answer 5

transfers energy without a transfer of mass

Question 6

what are the 2 types of waves?

Answer 6

longitudinal and transverse

Question 7

what is a longitudinal wave?

Answer 7

direction of oscillations is parallel to the direction of energy transfer

Question 8

what words refer to the regions of high and low density in a low density in a longitudinal wave?

Answer 8

compressions and rarefactions

Question 9

what is a transverse wave?

Answer 9

direction of oscillations is perpendicular to the direction of energy transfer

Question 10

for sound waves, what does pitch refer to?

Answer 10

the frequency of the sound wave

Question 11

or sound waves, what does loudness refer to?

Answer 11

the intensity of the sound wave, (which is proportional to the square of the amplitude)

Question 12

or sound waves, what does quality refer to?

Answer 12

the number and amplitude of the overtones of a fundamental frequency (stationary waves)

Question 13

what is a progressive wave?

Answer 13

longitudinal and transverse waves are both progressive
they progress through a medium and transfer energy
the amplitude of the vibration is the same at all points provided there is no loss in energy
phase varies with position

Question 14

what type of waves are EM aves?

Answer 14

transverse

Question 15

explain how a polarising filter can polarise EM waves

Answer 15

when unpolarised, EM waves oscillate in all directions perpendicular to the direction of energy propagation
when they pass through a polarising filter (aka a polaroid), only light that oscillates in 1 direction can pass through

Question 16

what is the “axis of transmission?”

Answer 16

the direction that polarised waves are polarised in

Question 17

how does water polarise light? and so how do polarised driving glasses work?

Answer 17

light incident on water (e.g. a wet road) is polarised horizontally. the reflected light is all reflected polarised parallel to the surface of the water.
polarised sunglasses work because they’re polarised vertically, so the light that oscillated horizontally cannot pass through

Question 18

2 sheets of polaroid (where directions of polarisation are aligned) are placed next to each other in front of an unpolarised light source. explain what would be observed when 1 of the filters is slowly rotated 180 degrees

Answer 18

at 0 degrees, the 2 axes of transmission are parallel, and the 2nd polaroid transmits all the polarised light that has passed through the 1st polaroid
as the 2nd polaroid is rotated, the amount of light getting through decreases, until 90 degrees where no light gets through, as axes of transmission of 2nd polaroid is perpendicular to the plane of polarisation of the incident light
as it is rotated from 90 to 180 degrees, the amount of light passing through increases until axes of transmission are realigned.

Question 19

why can longitudinal waves not be polarised?

Answer 19

in longitudinal waves, there is only 1 possible direction for oscillation (along the line of travel)

Question 20

_________ waves from a transmitter are plane polarised

Answer 20

radio and micro waves

Question 21

why must TV ariels be aligned properly?

Answer 21

TV ariels pic up radio waves
transmitted radio waves are plane polarised
for the signal to be optimal, the alignment of the ariel should be the same as the direction of polarisation of the radio waves.

Question 22

what is refraction?

Answer 22

the change in direction of the propagation of a wave when moving between 2 mediums with different optical densities

Question 23

a wave moves from air into glass
is the wave refracted towards or away from the normal?

Answer 23

towards the normal
glass is more optically dense than air

Question 24

what happens to the wave speed when a wave enters a more optically dense medium?

Answer 24

speed decreases

Question 25

what happens to the wavelength when a wave enters a more optically dense medium?

Answer 25

decreases

Question 26

what happens to the frequency when a wave enters a more optically dense medium?

Answer 26

remains constant

Question 27

what is Snell's law?

Answer 27

n1 sin(x1) = n2 sin(x2)

Question 28

define total internal reflection

Answer 28

when a ray of light in an optically dense medium is moving towards a boundary with a less optically dense medium and its completely reflected back into the more optically dense medium

Question 29

what are the 2 conditions for total internal reflection?

Answer 29

angle of incidence must be greater than the critical angle wave must be travelling towards a less optically dense medium than the one it is travelling in

Question 30

how is TIR used in optical fibres?

Answer 30

to transmit light along long optical fibres e.g. in an endoscope or in communications

Question 31

why is a highly transparent core used in optical fibres?

Answer 31

to minimise the absorption of light, to minimise the loss in amplitude of the waves

Question 32

why is a cladding used in optical fibres?

Answer 32

to reduce light loss from the core prevent signals passing into other fibres keeps signals secure is more less optically dense then the core reduces pulse broadening

Question 33

why is a very narrow core used in optical fibres?

Answer 33

prevent modal dispersion data transferred quicker less refraction out of core (as angle of incidence is less likely to fall below critical angle)

Question 34

why is a sheath around the cladding used in optical fibres?

Answer 34

to protect the fibre from scratches

Question 35

what is modal dispersion?

Answer 35

light that travels directly down the centre of the core of the fibre travels a different distance to light that repeatedly undergoes TIR light travelling at different angles reached the end of the fibre at different times, as the have the same speed but a different component of velocity parallel to the direction of the fibre so the light rays arrive at the end of the fibre at different times, which is called pulse broadening.

Question 36

what can be done to reduce modal dispersion?

Answer 36

use a thinner core

Question 37

what is material dispersion?

Answer 37

different frequencies of light have different speeds in the core (e.g. violet light travels slower in glass than red light) so they arrive at the end of the fibre at different times.

Question 38

how can material dispersion be reduced?

Answer 38

use monochromatic light

Question 39

what is the principle of superposition?

Answer 39

the resultant displacement at any point is the sum of the separate displacements due to the individual waves

Question 40

what does it mean if 2 waves are superimposed? | exam tecnique question

Answer 40

trick question - would lose marks in an exam if you said this correct term is superposed

Question 41

what is constructive interference?

Answer 41

when 2 waves of the same frequency and amplitude, and are in phase, add together, they reinforce each other and form a wave with 2x the amplitude

Question 42

what is destructive interference?

Answer 42

if 2 waves of the same amplitude and frequency are in antiphase and add together, they cancel out

Question 43

what does coherent mean?

Answer 43

same frequency and constant phase relationship

Question 44

what should be true about the wavelength o light and the gap it is passing through for diffraction to be greatest?

Answer 44

slit spacing should be approximately equal to wavelength

Question 45

how does iridescence work?

Answer 45

when light hits the surface, some is reflected and some is refracted. when the transmitted light hits the boundary on the other side of the film, so is then reflected. both beams of light are coherent. the 2 reflected beams of light superpose.

Question 46

how are stationary waves produced?

Answer 46

when 2 waves of a similar amplitude and the same frequency travel in opposte directions and superpose

Question 47

what happens when 2 waves travelling in opposite directions with the same frequency and and amplitudes meet in phase?

Answer 47

they interfere constructively an antinode is formed - this is maximum amplitude

Question 48

what happens when 2 waves travelling in opposite directions with the same frequency and and amplitudes meet in antiphase?

Answer 48

they interfere destructively a node is formed there is no displacement at nodes

Question 49

stationary waves can be used to ______ energy

Answer 49

store energy

Question 50

what is the first harmonic?

Answer 50

when a stationary wave forms on a string, and there is 1 node at either end (no nodes in between)

Question 51

what is diffraction?

Answer 51

the spreading out of waves through a gap

Question 52

describe the image formed on the screen during a single slit diffraction experiment

Answer 52

central bright fringe, with a width double that of all the other fringes intensity of fringes decreases as you move away from centre alternating light and dark fringes