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AQA A-Level Physics > Waves > Flashcards

Waves Flashcards

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
Polaroid filters
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
What is a transmission axis?
Axis of light that will be transmitted by the filter
27
What happens when visible light is sent through a pair of polaroid filters?
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
Application of Polarisation
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
Radio Aerials
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
Superposition
Two waves traveling through each other in the same region
31
Principle of superposition
Two waves travel through the same region, total displacement is equal to vector sum of individual displacements
32
Constructive interference
Waves are in phase Crests meet and lead to a resultant wave with a larger amplitude
33
Destructive interference
Waves are completely out of phase Crest of one wave meets trough of another Reducing amplitude to remaining resultant value
34
Reflection from a barrier
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
Stationary waves
Patterns of oscillations but crest of the wave does not appear to travel - do no transfer energy
36
How is a stationary wave formed?
Superposition of two travelling waves in opposite directions Equal speed, frequency and wavelength
37
Nodes
Points of stationary waves with zero displacements
38
Antinodes
Form halfway between nodes Points of oscillations with maximum amplitude
39
Difference between stationary points and progressive points? Stationary Points
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
Difference between stationary points and progressive waves? Progressive waves
Same frequency Varying amplitude Neighbouring points have a different phase Points separated by one wavelength are in phase
41
What is a harmonic?
Specific wavelengths which form stationary waves
42
Most simple stationary waves has? First harmonic
2 nodes and one anti nodes L = 1/2 wavelength
43
What is the first harmonic?
Lowest possible frequency of a stationary wave on a string
44
Equation for the first harmonic
f = 1/2L x Square root of T/μ f = frequency L = Length of string T = Tension μ = mass per unit length
45
Stationary waves in closed pipes
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
First harmonic in a closed pipe
n = 1 Node at closed part of the pipe Antinode at open part of the pipe L = 1/4 wavelength
47
Open pipe stationary sound waves
Open at both ends Antinodes on both ends First harmonic fits half a wave
48
Stationary Soundwaves
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
Stationary Microwaves
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
Why do microwave appliances commonly have a spinning table?
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
Diffraction
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
What happens if a wave diffracts from more than one gap?
Waves from the different gas superpose Waves interfere giving waves with lower or higher amplitude
52
Coherent Wave sources
Needed for a stable interference pattern Same frequency and constant phase difference
53
How to get a constant phase difference?
Use light from a laser Or Light from a bulb which has first been passed through a single slit
54
Example of incoherent light
Bulbs, LED's, flames and the sun
55
Laser safety procedures
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
Path length
Distance the waves travel along their paths
57
What determines the type of interference which occurs?
The phase dfference which depends on the path difference
58
What is path difference?
AP - BP
59

AQA A-Level Physics (9 decks)

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