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Physics > Waves > Flashcards

Waves Flashcards

1
Q

Transverse waves

A

Oscillations of particles are perpendicular to the direction of energy transfer

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2
Q

Longitudinal waves

A

Oscillations of particles are parallel to the direction of energy transfer

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3
Q

Examples of transverse waves

A

Electromagnetic waves
Water waves
Earthquake S waves

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4
Q

Examples of longitudinal waves

A

Sound waves
Earthquake P waves

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5
Q

What type of wave can be polarised?

A

Transverse

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6
Q

Applications of polarising waves

A

Signals from TV transmitters are sent polarised

Sunglasses

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7
Q

Why are signals from TV transmitters sent polarised?

A

So aerials only have to be aligned in one plane

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8
Q

How does a sound wave transmit energy through the area

A

-Energy is transferred by air molecules colliding
-Oscillations are parallel to the direction of energy transfer

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9
Q

What causes particles to move in a longitudinal wave?

A

There is a compression region of increased pressure which causes particles to move

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10
Q

Why can’t longitudinal waves be polarised?

A

-Transverse: perpendicular
-Longitudinal: parallel
-Polarisation is the restriction of displacement vector to one plane

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11
Q

Define the amplitude of a wave

A

The maximum displacement of the wave from the equilibrium position

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12
Q

What happens when a wave is polarised?

A

-The particles are only oscillating in one plane

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13
Q

How do polarising filters work?

A

There are small openings that can be orientated horizontally/vertically.

Vertical will only let waves oscillating vertically through
Horizontally will only let horizontal through

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14
Q

How to measure wave speed using 2 microphones

A

-set up 2 microphones a fixed distance apart
-Both connected to a computer
-The computer records when the first microphone heard the sound and then the second
-This gives a time measurement
Use c=f λ to find speed

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15
Q

How to measure wave speed by timing an echo

A

-Someone makes a loud noise opposite a flat wall
-You measure time it takes from the sound being made to you hearing the echo
-Then measure distance to the wall
-Remember to double the distance as the sound travels there and back

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16
Q

How to measure wave speed by timing a gunshot

A

-Someone shoots a starter pistol over a large distance
-Start timing when you see gun flash
-Stop timing when you hear the gunshot
-Measure distance

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17
Q

Conditions for creating a stationary wave

A

1) Superposition of 2 progressive waves travelling in opposite directions
2)With the same frequency/wavelength
3)And similar magnitude

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18
Q

What is a node?

A

Points of no displacement on stationary waves

Total destructive interference always occurs here.

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19
Q

What is an anti node?

A

Points of maximum displacement on stationary waves.

Constructive interference occurs here.

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20
Q

What is the distance between 2 nodes?

A

λ/2

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21
Q

What is the distance between 2 antinodes?

A

λ/2

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22
Q

Examples of stationary waves

A

-Strings on instruments eg guitars
-Insides of wind instruments
-Microwave ovens

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23
Q

When are points in phase in progressive waves?

A

-If the phase difference is 0, 360, 720 etc

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24
Q

When are points in anti-phase in progressive waves?

A

-If the phase difference is 180, 540 etc

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25
Q

Phase difference in stationary waves

A

2 points can only be in phase (360)
Or anti phase (180)

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26
Q

Progressive waves

A

Transfer energy

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27
Q

Differences between stationary and progressive waves

A

Stationary waves have nodes and antonodes, progressive waves don’t.

Progressive waves transfer energy, stationary waves don’t.

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28
Q

In practice, is the mass per unit length likely to change when tension is significantly increased?

A

-Stretching will cause the diameter to reduce
-This reduces the mass per unit length

29
Q

How does increasing tension affect fundamental frequency?

A

It increases

30
Q

How does increasing mass per unit length affect fundamental frequency ?

A

Decreases

31
Q

How does increasing length of string affect fundamental frequency?

A

Decreases

32
Q

How do you get maximum diffraction?

A

If the gap is the same as the wavelength

33
Q

What happens if the gap is a bit larger than the wavelength?

A

There will be some diffraction

34
Q

What happens if the gap is significantly larger than the wavelength?

A

No diffraction

35
Q

What happens if the gap is the same as the wavelength?

A

Maximum diffraction

36
Q

What type of interference causes dark fringes?

A

Destructive interference

37
Q

What type of interference causes bright fringes?

A

Constructive interference

38
Q

What is constructive interference?

A

Waves from across the width of the slit arrive at the screen in phase.

39
Q

What is destructive interference?

A

Waves from across the width of the slit arrive at the screen in anti-phase

40
Q

What is the brightest part of the intensity graph called?

A

Central maximum

41
Q

What is the central maximum?

A

The brightest part of the intensity graph

42
Q

Monochromatic

A

The light is all the same wavelength so the amount of diffraction will be the same.

43
Q

Coherent

A

The light has the same frequency and a fixed phase difference

44
Q

How to calculate distance between slits

A

d=1/N
N= Number of lines per metre.
d= Distance between slits

45
Q

Maximum order equation

A

Nmax=d/λ

Always round answer down to nearest integer

46
Q

Maximum order equation

A

dsinθ=nλ

47
Q

Where does the light bend going from a lower refractive index to a higher refractive index

Low to high

A

Light bends towards normal

48
Q

Where does the light bend going from a higher refractive index to a lower refractive index

High to low

A

Light bends away from normal

49
Q

What happens when a wave passes into a denser material

A

It slows down and wavelength decreases

50
Q

How to calculate refractive index using wave speeds

A

n=c/cs
cs= speed of wave in the material

51
Q

How does frequency change in refraction?

A

Stays the same

52
Q

Snells law

A

n1sinθ1=n2sinθ2

53
Q

How to calculate relative refractive index. (Refractive index going from material 1 to material 2)

A

1n2=n2/n1

54
Q

Refractive index of air

A

1

55
Q

Rearrangement of Snell’s law that includes wave speed.

A

n1/n2=c2/c1

56
Q

When does total internal reflection happen?

A

angle of incidence > critical angle

Wave is travelling from a higher to lower refractive index

57
Q

Critical angle equation

A

Sinθc=n2/n1

58
Q

How to fibre optic cables work?

A

They use total internal reflection to send messages at the speed of light.

The core has a high refractive index.
Cladding has a low refractive index.

Light hits and an angle greater than critical so TIR always happens

59
Q

Advantages of fibre optic cables

A

Higher frequency so more info

Light doesn’t heat fibre so no energy lost as heat

No electrical interference

Cheaper to produce

Signal can travel a long way without signal loss

60
Q

Modal dispersion

A

Signal can get wider due to dispersion of light.

One part of the signal travels further than another part so they don’t reach the end at the correct time

61
Q

Material dispersion

A

Dispersion due to different wavelengths being diffracted by different amounts.

62
Q

Solution of material dispersion

A

Use monochromatic light so amount of refraction is the same

63
Q

Solution of modal dispersion

A

Use signal boosters

64
Q

Explain how path difference can cause a minimum

A

-Path difference is (n+1/2) λ
-So waves arrive in antiphase
-So destructive interference occurs

65
Q

How to calculate the wavelength of a stationary wave

A

Multiple distance by 2
Divide by the number of loops

66
Q

Suggest a light source that would emit a continuous spectrum

A

-Sun
-Filament lamp

67
Q

Blue vs red wavelength

A

Blue had a shorter wavelength

68
Q

Diffracting white light

A

White central maxima
Dark fringe
Blue
Red

Physics (7 decks)

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