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waves Flashcards

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1
Q

what is a wave

A

an oscillation of particles or fields

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2
Q

what is a progressive wave

A

A progressive (moving) wave carries energy from one place to another without transferring any material.

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3
Q

what is a cycle of a wave

A

one complete vibration of the wave

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4
Q

what is wavelength

A

Wavelength, l, metres — the length of one whole wave cycle, from crest to crest or trough to trough.

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5
Q

what is the time period of a wave

A

Period, T, seconds — the time taken for a whole cycle (vibration) to complete, or to pass a given point.

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6
Q

what is the frequency of a wave

A

Frequency, f, hertz — the number of cycles (vibrations) per second passing a given point.

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7
Q

what is the phase of the wave

A

Phase — a measurement of the position of a certain point along the wave cycle.

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8
Q

what is the phase difference of a wave

A

Phase difference — the amount one wave lags behind another.

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9
Q

what is reflection of a wave

A

Reflection — the wave is bounced back when it hits a boundary

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10
Q

what Is refraction a wave

A

Refraction — the wave changes direction as it enters a different medium. The change in direction is a result of the wave slowing down or speeding up.

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11
Q

frequency equation

A

f = 1/ T

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12
Q

how to work out the wave speed

A

wave speed = distance travelled/ time taken

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13
Q

how to work out speed of a wave

A

speed of wave = wavelength x frequency

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14
Q

what is the speed of a em wave in a vacuum

A

c = 3.00 × 108 ms–1

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15
Q

what are transverse waves

A

waves with vibrations perpendicular to the direction of energy transfer.

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16
Q

give an example of a transverse wave

A

em waves

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17
Q

what are longitudinal waves

A

waves with oscillations parallel to the energy transfer

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18
Q

give an example of a longitudinal wave

A

sound waves

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19
Q

what is polarisation

A

when vibrations are restricted to one plane

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20
Q

what waves can you polarise

A

transverse waves

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21
Q

what is evidence that electromagnetic waves are transverse

A

polarisation

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22
Q

how can you polarise waves

A

using a polarising filter

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23
Q

if you have two polarising filters at right angles to each other what happens

A

no light will get through

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24
Q

how do polaroid glasses work

A

Polaroid sunglasses reduce the glare of light reflected by water or glass. The reflected light is polarised and the intensity is reduced when it passes through the polaroid sunglasses.

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25
Q

why are the rods on a tv aerial horizontal

A

TV signals are polarised by the orientation of the rods on the broadcasting aerial. To receive a strong signal, you have to line up the rods on the receiving aerial with the rods on the transmitting aerial — if they aren’t aligned, the signal strength will be lower.

26
Q

what is superposition

A

the instant the waves cross, the displacements due to each wave combine. Then each wave moves on

27
Q

what is the principle of superposition

A

when two or more waves cross the resultant displacement equals the vector sum of the individual displacements

28
Q

a crest pus a crest and a trough plus a trough is a example of what

A

constructive interference

29
Q

a crest plus a trough is an example of what

A

destructive interference

30
Q

for interference to be noticeable what should be true about the amplitudes

A

the amplitudes should be nearly equal

31
Q

what does it mean if two points are in phase

A

if they are both at the same point in the wave cycle

32
Q

what is true about the points displacement and velocity if the points are in phase

A

same displacement and velocity

33
Q

what angle should you use to show 1 complete cycle of a wave

A

360 or 2 pi

34
Q

how do you know two points are in phase

A

the have a phase difference of zero or a multiple of 360

35
Q

how do you know two points are exactly out of phase

A

have phase difference of odd number multiples of 180

36
Q

how can you get a clear interference pattern

A

the two or more sources must be coherent and be in phase

37
Q

what does it mean to be coherent

A

to have the same wavelength and frequency and a fixed phase difference between them

38
Q

what does getting a constructive or destructive interference at a point depend on

A

how much further one wave travelled that the other wave to get to that point

39
Q

what is path difference

A

The difference in distance travelled by two waves from their sources to the point where they meet

40
Q

when will you get constructive interference

A

At any point an equal distance from two
sources that are coherent and in phase or where the path difference is a whole number of wavelengths.

41
Q

where do you get destructive interference

A

But at points where the path difference is half a wavelength, one and a half wavelengths, two and a half wavelengths etc., the waves arrive out of phase and you get destructive interference.

42
Q

when do you get constructive interference (equation)

A

path difference = nλ

43
Q

where do you get destructive interference (equation)

A

path difference + (2n + 1)λ /2

44
Q

what is a stationary wave

A

superposition of two progressive waves with the same frequency (wavelength), moving in opposite directions.

45
Q

what happens with stationary waves that doesn’t happen with progressive waves

A

no energy is transmitted

46
Q

what are nodes

A

where amplitude is zero

47
Q

what are antinodes

A

points of maximum amplitude

48
Q

what is diffraction

A

the way waves spread out as they come through a narrow gap or go around obstacles

49
Q

what does the amount of diffraction depend on

A

depends on the wavelength of the wave compared to the size of the gap

50
Q

what happens to the diffraction when the gap is a lot bigger than the wavelength

A

diffraction is unnoticeable

51
Q

what happens to diffraction when you have a gap several wavelengths wide

A

you get noticeable diffraction

52
Q

what happens to diffraction when the size of the gap is roughly the same size as the wavelength

A

you get the most diffraction

53
Q

what happens to diffraction if the size of the gap is smaller than the wavelength

A

no diffraction an the waves are mostly reflected back

54
Q

to get a clear diffraction pattern for light what do you need to do

A

use a monochromatic coherent light source

55
Q

what does monochromatic mean

A

the light has all the same wavelength so its the same colour

56
Q

what is an example of a monochromatic coherent light source

A

lasers

57
Q

what happens you shine light through a narrow slit

A

you get a diffraction pattern that has a central bright fringe with dark and bright fringes alternating on either side where the bright and dark fringes are created by destructive and constructive interference

58
Q

what happens when you diffract white light through narrow slit

A

you get a diffraction pattern of a central bright white fringe where the fringes are a spectra of colours with blue on the inner side and red on the outer side and fringes getting fainter the further you move outwards

59
Q

why do you get that specific diffraction pattern for white light when shone through a narrow slit

A

because white light is a mixture of colours each with different wavelengths so when diffracted all the wavelengths are diffracted by different amounts

60
Q

what happens to central maximum if you decrease slit width

A

you decrease the amount of diffraction and so the central maximum is narrower and the intensity of the central maximum is higher

61
Q
A

physics (11 decks)

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