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AS Physics > Definitions 3 > Flashcards

Definitions 3 Flashcards

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1
Q

Progressive waves

A

Waves that transfer energy, but not matter, as a result of oscillations

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2
Q

Transverse waves

A

Waves in which the particles oscillate perpendicular to the direction of motion and energy transfer

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3
Q

Longitudinal waves

A

Waves in which the particles oscillate parallel to the direction of motion and energy transfer

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4
Q

Frequency

A

The number of oscillations of a wave per unit time

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5
Q

Period

A

The time taken for one complete oscillation

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6
Q

Amplitude

A

The maximum distance of a particle of a wave from its equilibrium or rest position

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7
Q

Displacement

A

The distance of a point on a wave from its rest or equilibrium position

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8
Q

Phase difference

A

The difference in positions of two points on a wave or between two points on two difference waves - it indicates how much one wave is ahead of or behind another

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9
Q

Intensity

A

The power per unit area

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10
Q

Doppler effect

A

The change in observed frequency when a source of sound waves moves relative to a stationary observer

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11
Q

Electromagnetic waves

A

Transverse waves that travel at the speed of light in a vacuum

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12
Q

Polarisation

A

The restriction of the oscillations of the particles of a transverse wave to only one direction, which still perpendicular to its motion

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13
Q

State the properties of standing waves:

A
  1. Standing waves do not transfer energy
  2. Standing waves consist of nodes and antinodes
  3. All points between adjacent nodes oscillate in phase
  4. All points in adjacent loops oscillate in anti-phase
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14
Q

Wavelength

A

The distance between two points that are in phase with each other on consecutive oscillations of a wave

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15
Q

What happens when the time-base or voltage unit on a cathode-ray oscilloscope turns off?

A
  1. If the time-base unit turns off a straight vertical line will show
  2. If the voltage turns unit off you will see a straight horizontal line
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16
Q

What is the relationship between frequency and wavelength?

A

For a wave at constant speed, λ ∝ 1 / f, so when λ increases, f decreases and vice versa

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17
Q

State the relationships between intensity, amplitude and frequency:

A
  1. I ∝ A^2
  2. I ∝ f^2
  • If A or fdoubles, intensity increases by afactor of 4
  • If A or f ishalved, intensity becomes1/4as much
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18
Q

What is the relationship between the intensity and distance of a spherical wave?

A

The area of a spherical wave passes through the surface area of a sphere, so A = 4πr^2, hence:
I = P / 4πr^2
If no energy is absorbed, we get:
I ∝ 1 / r^2

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19
Q

Why can’t longitudinal waves be polarised?

A

The particles of a longitudinal wave oscillate parallel to the direction of energy transfer, which means they are already moving one direction

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20
Q

What occurs when unpolarised light meets a polariser?

A

The intensity of unpolarised light will decrease be 1/2 when it moves through a polariser

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21
Q

What occurs if a polariser and an analyser have the same orientation?

A

If a polariser and an analyser have the same orientation, the transmission axes of both filters are 0° or 180° to each other, which means that the intensity of the incident light equals that of the transmitted light, since cos(0° or 180°) = 1

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22
Q

What if a polariser and an analyser are at right angles?

A

If a polariser and analyser are at right angles, the transmission axes of both filters are 90° or 270° to each other, and so as cos(90° or 270°) = 1, the intensity of the transmitted by the analyser will be zero

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23
Q

State the equation for polarisation:

A

I = Io * cos^2(θ)

θ = the angle between the direction of the incident light and the transmission axis of the polariser or analyser

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24
Q

What is the formula for the length of a stationary wave that is fixed at both ends?

A

L = nλ / 2, where n = all positive integers

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25
What is the formula for the length of a stationary wave that is open at one end?
L = nλ / 4, where n = only odd positive integers
26
Why do stationary waves that are open at one end only have odd harmonics?
There is always a node at the closed end and an antinode at the open end, which causes only odd multiples of (1/4)λ to be added to each successive harmonic
27
What is the formula for the length of a stationary wave that is open at both ends?
L = nλ / 2, where n = all positive integers
28
What happens to a wave when it is diffracted?
The intensity and therefore the amplitude of the wave decreases - all other properties remain the same
29
Path difference
The difference in distance one wave has to travel compared to another to reach the same point
30
How do you calculate the path difference for constructive interference?
Constructive interference = nλ
31
How do you calculate the path difference for deconstructive interference?
Deconstructive interference = (n +1/2)λ
32
How do you calculate the angle between a maxima and the central maxima?
θ = tan-1(h / D) h = n * x, where x is the distance between successive maxima D = the distance from the slits to the screen
33
What do maxima points look like?
They are bright brands of light that are evenly spaced out from each other and decrease in intensity from either side of the central central maxima
34
How do you identify areas of compression and rarefaction on a displacement time graph?
Areas of compression and rarefaction always appear when the displacement is zero
34
How do you identify an area of compression?
If the displacements above and below the point are coming towards each other, the point is an area of compression
35
How do you identify an area of rarefaction?
If the displacements above and below the point are moving away from each other, the point is an area of rarefaction
36
What are the conditons for superposition?
1. The waves must be of the same type 2. The waves must be coherent 3. The waves must be travelling in opposite directions
37
Monochromatic light
Light that is of a single wavelength
38
How do you calculate phase difference?
P.D = 360° * ( x/λ or t/T ) x = path difference between two points t = the time difference between two points Note that to calculate the phase difference between two waves, they should have the same frequency as each other
39
What is a cathode-ray oscilloscope?
An instrument that displays a voltage against time graph for an electric circuit
40
Derive the equation v = fλ:
1. The speed of a wave is given by v = d / t 2. A wave travels one wavelength in one period, hence, v = λ / T 3. If you substitute f = 1 / T into v = λ / T, the equation becomes v = fλ
41
How do you calculate the intensity of a wave?
I = P / A, where A is the perpendicular area to the motion or energy transfer of the wave
42
State the differences between transverse and longitudinal waves:
1. Transverse wave particles move perpendicular, while longitudinal wave particles travel parallel to the energy transfer of the wave 2. Transverse waves have crests and troughs, while longitudinal waves have compressions and rarefactions 3. Transverse waves can travel through a vacuum, but longitudinal waves cannot 4. Transverse waves can be polarised, but longitudinal waves cannot
43
What are areas of rarefaction and compression?
1. A rarefaction is an area of low pressure, with the particles being further apart from each other 2. A compression is an area of high pressure, with the particles being closer to each other
44
What happens when a source of sound waves moves closer to an observer?
The wavelength of the sound waves shorten and compress, therefore increasing the observed frequency
45
What happens when a source of sound waves moves away from an observer?
The wavelength of the sound waves lengthen and broaden, therefore decreasing the observed frequency
46
State the equation for the Doppler effect:
fo = fs [ vs / ( vs ± v ) ] vs = 340ms^-1
47
What happens to EM waves as their frequency decreases?
The higher the frequency of an EM wave (or the smaller the wavelength), the more energy that it possesses, which makes it more ionising or harmful to living cells and cause cancer
48
Superposition
Superposition occurs when two or more waves overlap when they come together
49
The principle of superposition
When two or more coherent waves overlap, the total displacement at any point is equal to the sum of the individual displacements from each wave
50
Stationary waves
Stationary waves are waves produced from the superposition of two coherent waves of the same amplitude that are travelling in opposite directions
51
Nodes
Fixed points on a stationary wave where there is no vibration
52
Antinodes
Antinodes are points on a stationary wave with maximum vibration that only move in the vertical direction
53
How do you increase the harmonic of a stationary wave?
Increase the frequency of the stationary wave as this will also increase at the wavelength and the number of nodes and antinodes present - decreasing the frequency does the opposite
54
What is diffraction affected by?
Diffraction is dependent on the width of the gap compared to the wavelength of the waves: 1. When the wavelength ≈ the gap width, diffraction is strong - there is a great amount of diffraction with a clear, distinctive structure 2. When the wavelength much > the gap width, diffraction is even stronger - the wave spread out the most, but there is a less detailed structure 3. When the wavelength is < the gap width, there is less diffraction
55
Inteference
Interference refers to the observable results of superposition - when two or more waves overlap and produce a new wave pattern
56
Constructive and deconstructive interference
1. Constructive interference - occurs when two or more waves are in phase, producing a resultant wave that has twice the amplitude 2. Deconstructive interference - occurs when two or more are in anti-phase, producing in a resultant wave that has no amplitude
57
Coherence
Coherent waves have the same frequency and a constant phase difference
58
What are the requirements for two source interference?
1. The sources must be coherent 2. The sources must be monochromatic
59
What is Young's double slit equation?
λ = ax / D a = distance between the centres of the slits x = distance between two adjacent maxima or minima D = distance between the slits and the screen
60
What is the diffraction grating equation?
dsin(θ) = nλ d = distance between the centres of two adjacent slits θ = angular separation between the order of maxima in and the central maxima n = order of maxima (0,1,2...)
61
What is represented by N in diffraction gratings?
N is the number of lines per mm, m, cm: d = 1 / N
62
How do you find the highest order of maxima visible?
The highest order of maxima visible is given by n = d/λ, as θ = 90° and sin(90°) = 1 - n must be a positive integer
63
What are the conditions for forming a stationary wave?
1. The waves must be travelling in opposite directions 2. The waves are coherent 3. The waves have the same amplitude
64
What is the equation, which relates the intensity and amplitude of a wave?
I’ / I = ( A’ / A )^2, where I’ and A’ are the altered values

AS Physics (3 decks)

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