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AQA A-Level Physics > Waves > Flashcards

Waves Flashcards

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1
Q

Equilibrium Position

A

Position of the wave when no energy is being transferred through it

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2
Q

Displacement

A

Distance + direction of a vibrating particle from its equilibrium position

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3
Q

Amplitude

A

Maximum displacement of a vibrating particle

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4
Q

Wavelength

A

The least distance between two particles with the same displacement and velocity

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5
Q

Time period

A

The time for one complete wave to pass a fixed point

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6
Q

Frequency

A

The number of complete waves passing a point per second

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7
Q

Equation for frequency

A

f(Hz) = 1/T(s)

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8
Q

Wave speed

A

Speed at which the wave propagates

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9
Q

Equation for wave speed

A

c = frequency x wavelength

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10
Q

Speed of light in a vacuum

A

3 x 10^8

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11
Q

Phase Difference

A

The fraction of a cycle between the vibrations of two particles

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12
Q

What is phase difference measured in

A

Radians
2pi = one complete cycle

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13
Q

Phase of a vibrating particle

A

Fraction of its cycle it has completed since the start

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14
Q

In phase

A

when two points on a wave oscillate with the same displacement and velocity at the same time
Phase difference = 2pi raidans

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15
Q

Antiphase

A

Two points on a wave oscillate with equal but opposite displacement and velocity at the same time
Phase difference = pi radians

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16
Q

Path difference

A

The difference in length between two paths in terms of wavelengths

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17
Q

Progressive Waves

A

Transfer energy but no net movement of the medium that carried the wave
Particles of the medium oscillate around equilibrium position

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18
Q

Transverse Waves

A

The oscillations of the wave are perpendicular to the direction of energy transfer

Can be polarised

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19
Q

Example of transverse waves

A

Water, electromagnetic, seismic and waves on a string

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20
Q

Longitudinal waves

A

Oscillations of the wave are parallel to the direction of energy transfer

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21
Q

Compression

A

Region of relatively high density and pressure in a longitudinal wave

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22
Q

Rarefaction

A

Region of relatively low density and pressure in a longitudinal wave

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23
Q

Polarisation

A

Perpendicular oscillations to wave propagation van happen in different planes

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24
Q

EM waves consist of?

A

Perpendicular oscillating electric and magnetic fields

Also perpendicular to wave propagation

Diagrams typically only show electric field

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25
Q

Polaroid filters

A

Used to polarise visible light

Absorbs polarisation components of the light which are perpendicular to the axis of the filter

Transmit polarisation components of light which are parallel to the axis of the filter

26
Q

What is a transmission axis?

A

Axis of light that will be transmitted by the filter

27
Q

What happens when visible light is sent through a pair of polaroid filters?

A

First filter will be vertically polarised and the same for the second

Transmitted light will be vertically polarised and intensity is at a maximum

If the second filter is horizontal plane then the vertically polarised light by the first filter will be polarised perp to the direction

Light will be completely absorbed

28
Q

Application of Polarisation

A

Light reflected of horizontal surfaces like water are partially polarised horizontally

Polaroid sunglasses are designed to absorb this polarisation of light

Microwaves an be polarised using metal grids due to very long wavelengths

29
Q

Radio Aerials

A

Radio waves and microwaves produced by an antenna typically polarised - if antenna is vertical then EM waves are vertically polarised

Polarisation allows two antennas to send out signs of same frequency without interference due to different polarisation

30
Q

Superposition

A

Two waves traveling through each other in the same region

31
Q

Principle of superposition

A

Two waves travel through the same region, total displacement is equal to vector sum of individual displacements

32
Q

Constructive interference

A

Waves are in phase

Crests meet and lead to a resultant wave with a larger amplitude

33
Q

Destructive interference

A

Waves are completely out of phase

Crest of one wave meets trough of another

Reducing amplitude to remaining resultant value

34
Q

Reflection from a barrier

A

When a wave reaches a barrier it reflects thus creating a pulse in opposite direction

Has equal and opposite displacement so there is always destructive interference

35
Q

Stationary waves

A

Patterns of oscillations but crest of the wave does not appear to travel - do no transfer energy

36
Q

How is a stationary wave formed?

A

Superposition of two travelling waves in opposite directions
Equal speed, frequency and wavelength

37
Q

Nodes

A

Points of stationary waves with zero displacements

38
Q

Antinodes

A

Form halfway between nodes

Points of oscillations with maximum amplitude

39
Q

Difference between stationary points and progressive points?

Stationary Points

A

Stationary points
- Same frequency
- Same amplitude
- Points which lie between adjacent nodes have same phase
- Points on either side are 180 degrees out of phase

40
Q

Difference between stationary points and progressive waves?

Progressive waves

A

Same frequency
Varying amplitude
Neighbouring points have a different phase
Points separated by one wavelength are in phase

41
Q

What is a harmonic?

A

Specific wavelengths which form stationary waves

42
Q

Most simple stationary waves has?

First harmonic

A

2 nodes and one anti nodes

L = 1/2 wavelength

43
Q

What is the first harmonic?

A

Lowest possible frequency of a stationary wave on a string

44
Q

Equation for the first harmonic

A

f = 1/2L x Square root of T/μ

f = frequency
L = Length of string
T = Tension
μ = mass per unit length

45
Q

Stationary waves in closed pipes

A

One sealed end and on open

Oscillations at closed end have 0 amplitude as particles have nowhere to go

Open end has antinode as pressure drops to equilibrium atmospheric pressure

46
Q

First harmonic in a closed pipe

A

n = 1
Node at closed part of the pipe
Antinode at open part of the pipe

L = 1/4 wavelength

47
Q

Open pipe stationary sound waves

A

Open at both ends
Antinodes on both ends

First harmonic fits half a wave

48
Q

Stationary Soundwaves

A

Continuous soundwaves reflect from a hard surface at a normal incidence

Stationary produced as the hard surface acts like the end of a pipe

49
Q

Stationary Microwaves

A

Reflect a metal sheet

Microwaves directed at a metal sheet at 90 using a microwave transmitter which are reflected by a metal sheet leading to a stationary wave

50
Q

Why do microwave appliances commonly have a spinning table?

A

Receiver placed between transmitter and sheet and is then moved backwards and forwards, there is a strong microwave signal at antinodes and no signal at nodes

51
Q

Diffraction

A

Wave passes through a narrow gap of almost 0 width

Spread out on the other side of the gap

Wave emerges as semi-circular and equal amplitude

52
Q

What happens if a wave diffracts from more than one gap?

A

Waves from the different gas superpose

Waves interfere giving waves with lower or higher amplitude

52
Q

Coherent Wave sources

A

Needed for a stable interference pattern

Same frequency and constant phase difference

53
Q

How to get a constant phase difference?

A

Use light from a laser

Or

Light from a bulb which has first been passed through a single slit

54
Q

Example of incoherent light

A

Bulbs, LED’s, flames and the sun

55
Q

Laser safety procedures

A

Do not point the laser at anybody else
Do not look directly along the beam
Make sure laser cannot be reflected into your eyes

56
Q

Path length

A

Distance the waves travel along their paths

57
Q

What determines the type of interference which occurs?

A

The phase dfference which depends on the path difference

58
Q

What is path difference?

A

AP - BP

59
Q
A

AQA A-Level Physics (9 decks)

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