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Waves Flashcards

(69 cards)

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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
Phase difference in stationary waves
2 points can only be in phase (360) Or anti phase (180) All points between 2 adjacent nodes are in phase
26
Progressive waves
Transfer energy from one place to another without transferring material
27
Differences between stationary and progressive waves
Stationary waves have nodes and antonodes, progressive waves don’t. Progressive waves transfer energy, stationary waves don’t.
28
In practice, is the mass per unit length likely to change when tension is significantly increased?
-Stretching will cause the diameter to reduce -This reduces the mass per unit length
29
How does increasing tension affect fundamental frequency?
It increases
30
How does increasing mass per unit length affect fundamental frequency ?
Decreases
31
How does increasing length of string affect fundamental frequency?
Decreases
32
How do you get maximum diffraction?
If the gap is the same as the wavelength
33
What happens if the gap is a bit larger than the wavelength?
There will be some diffraction
34
What happens if the gap is significantly larger than the wavelength?
No diffraction
35
What happens if the gap is the same as the wavelength?
Maximum diffraction
36
What type of interference causes dark fringes?
Destructive interference
37
What type of interference causes bright fringes?
Constructive interference
38
What is constructive interference?
Waves from across the width of the slit arrive at the screen in phase.
39
What is destructive interference?
Waves from across the width of the slit arrive at the screen in anti-phase
40
What is the brightest part of the intensity graph called?
Central maximum
41
What is the central maximum?
The brightest part of the intensity graph
42
Monochromatic
The light is all the same wavelength so the amount of diffraction will be the same.
43
Coherent
The light has the same frequency and a fixed phase difference
44
How to calculate distance between slits
d=1/N N= Number of lines per metre. d= Distance between slits
45
Maximum order equation
Nmax=d/λ Always round answer down to nearest integer
46
Maximum order equation
dsinθ=nλ
47
Where does the light bend going from a lower refractive index to a higher refractive index Low to high
Light bends towards normal
48
Where does the light bend going from a higher refractive index to a lower refractive index High to low
Light bends away from normal
49
What happens when a wave passes into a denser material
It slows down and wavelength decreases
50
How to calculate refractive index using wave speeds
n=c/cs cs= speed of wave in the material
51
How does frequency change in refraction?
Stays the same
52
Snells law
n1sinθ1=n2sinθ2
53
How to calculate relative refractive index. (Refractive index going from material 1 to material 2)
1n2=n2/n1
54
Refractive index of air
1
55
Rearrangement of Snell’s law that includes wave speed.
n1/n2=c2/c1
56
When does total internal reflection happen?
angle of incidence > critical angle Wave is travelling from a higher to lower refractive index
57
Critical angle equation
Sinθc=n2/n1
58
How to fibre optic cables work?
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
Advantages of fibre optic cables
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
Modal dispersion
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
Material dispersion
Dispersion due to different wavelengths being diffracted by different amounts.
62
Solution of material dispersion
Use monochromatic light so amount of refraction is the same
63
Solution of modal dispersion
Use signal boosters
64
Explain how path difference can cause a minimum
-Path difference is (n+1/2) λ -So waves arrive in antiphase -So destructive interference occurs
65
How to calculate the wavelength of a stationary wave
Multiple distance by 2 Divide by the number of loops
66
Suggest a light source that would emit a continuous spectrum
-Sun -Filament lamp
67
Blue vs red wavelength
Blue had a shorter wavelength
68
Diffracting white light
White central maxima Dark fringe Blue Red
69
Double slit equation
W=lambda D / s Lambda= wavelength D= distance from slits to screen S= Slit separation (distance between centres of slits)

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