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A Level Physics > 05-waves > Flashcards

05-waves Flashcards

1
Q

What is a wave’s amplitude?

A

The amplitude of a wave is its maximum displacement from its equilibrium position.

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2
Q

What is a wave’s frequency?

A

The frequency of a wave is the number of complete waves that pass a point per second.

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3
Q

What is meant by the period of a wave?

A

The period of a wave is the length of time taken for one complete wave to pass a given point.

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4
Q

How are frequency and period linked?

A

Frequency = 1/Period
They are reciprocals of each other.

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5
Q

What is wavelength?

A

The distance between the same point on two adjacent waves (for example peak-peak or trough-trough).

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6
Q

State the equation used to calculate a wave’s speed.

A

v= f x λ
Speed = Frequency × Wavelength

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7
Q

Describe a longitudinal wave.

A

• Particle oscillations are parallel to the direction of the wave’s motion
• Consists of rarefactions (low pressure regions), and compressions (high pressure regions)

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8
Q

Describe a transverse wave.

A

• Particle oscillations are perpendicular to the direction of the wave’s motion
• Consists of peaks (maximum positive displacement) and troughs (maximum negative displacement)

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9
Q

What is a progressive wave?

A

A progressive wave is one that transfers energy from one point to another without any transfer of matter.

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10
Q

What is a standing wave?

A

A wave that stores energy rather than transferring it from one place to another.

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11
Q

What is path difference a measure of?

A

Path difference is a measure of how far ahead one wave is compared to another.

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12
Q

What is a wave’s phase?

A

A wave’s phase at a given point is a measure of how far through its cycle the wave is. It is usually measured in radians, where a complete cycle is π

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13
Q

What is the phase difference between two waves at a given point?

A

The phase difference is the difference between the phases of the two waves - in other words, it is a measure of the difference between how far each wave is through its cycle.

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14
Q

What happens when two waves meet?

A

The two waves will interfere with each other.

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15
Q

What happens when two waves meet in phase?

A

They will interfere and undergo constructive interference.

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16
Q

What happens when two waves meet in antiphase?

A

They will interfere and undergo destructive interference.

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17
Q

How is a standing wave formed on a string?

A

• A wave reflects from a closed end meaning two identical waves are travelling in opposite directions down the same string
• At points where the waves meet in phase, constructive interference occurs and an antinode is formed
• At points where the waves meet in antiphase, destructive interference occurs and a node is formed

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18
Q

What is a node?

A

A node is a point of minimum displacement - there is no movement from the equilibrium position.

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19
Q

What is an antinode?

A

An antinode is a point of maximum displacement.

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20
Q

What two factors does the speed of a transverse wave on a string depend on?

A
  1. Tension
  2. Mass per unit length of the string
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21
Q

State the equation used to calculate the speed of a transverse wave on a string.

A

v=√(T/μ)

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22
Q

State the equation used to calculate intensity.

A

I = P/A
P is the power
A is the area

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23
Q

What is the refractive index of a material through which light travels a speed of ‘v’?

A

n = c/v
Where c is the speed of light in a vacuum.

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24
Q

State the equation linking the refractive indexes and angles at an interface between two mediums.

A

n1 sin θ1 = n2 sin θ2

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25
Q

What is the critical angle?

A

The angle of incidence for which the angle of refraction is 90° and all the light passes along the boundary between the mediums. Beyond this angle all light will be reflected.

26
Q

State the equation used to calculate a critical angle.

A

sinC = 1/n

27
Q

What is total internal reflection and when does it happen

A

Total internal reflection is where all the light is reflected back at the boundary between two mediums. It occurs when light is incident at an angle greater than the critical angle.

28
Q

What is the focal point of a converging lens?

A

The single point where the parallel rays of light entering the lens converge to.

29
Q

What is the focal length of a lens?

A

The distance between the centre of the lens and the focal point.

30
Q

What is the equation used to calculate the power of a lens?

A

Power = 1/Focal Length

31
Q

What is a real image?

A

A real image is one that can be projected onto a screen and is always inverted.
Real images are the consequence of light meeting at a focal point.

32
Q

What is a virtual image?

A

Virtual images are the consequence of rays of light appearing to meet at a point.
They cannot be projected onto a screen.

33
Q

State the equation used to calculate the magnification of an image.

A

Magnification = Image Height / Object
Height

34
Q

Frequency equation

A

F = 1 / T
T = time period

35
Q

What are the wavelength of each electro magnetic radiation?

A

Radio = 1 x 10^3m
Microwaves = 1 x 10^-2m
Infrared waves = 1 x 10^-5m
Visible light = 1 x 10^-7m
Ultraviolet = 1 x 10^-8m
X ray = 1 x 10^-10m
Gamma rays = 1 x 10^-12m

36
Q

What is superposition?

A

Where the waves overlap

37
Q

What is the path difference for constructive interference?

A

Path difference = n λ
Where n is an integer

38
Q

What is the formula for the minimum path difference for destructive interference?

A

(n + 1/2) λ

39
Q

What is the principle of superposition?

A

Where two or more waves meet, the total displacement at any point is the sum of their displacements that each individual wave would cause at that next point

40
Q

What is a coherent wave?

A

When the phase difference doesn’t change

41
Q

What is an incoherent wave?

A

If the phase difference keeps changing

42
Q

What is the difference between stationary waves in close pipes and in strings/open pipes

A

In a closed pipe, the harmonic must start at the node.
In a closed pipe, there must be an odd number of harmonics.

43
Q

If light is travelling from dense to a less dense object, what will the refractive index be?

A

<1
Denser object = higher refractive index

44
Q

If light is travelling from a less dense object to a more dense object, what will the refractive index be?

A

> 1

45
Q

If the light was in the opposite direction from medium 2 to medium one, what will the refractive index be?

A

If the light travels in the opposite direction from medium 2 to medium one, the refractive index is the reciprocal of medium one to medium two

46
Q

What is the absolute refractive index?

A

The refractive index for light travelling from a vacuum into that material

47
Q

What type of image will be produced if the image is beyond the focal point of a convex lens

A

Always real, always inverted, diminished/magnified

48
Q

What type of image will be produced if the image is before the focal point of a convex lens

A

Always virtual, always upright, always magnified

49
Q

What type of image is produced for a concave lens?

A

Always virtual, always diminishing, always upright

50
Q

What does it mean if the focal length is :positive; negative

A

If positive = converging lens
If negative = diverging lens

51
Q

What type of image is produced if the image distance is positive or negative

A

+ = real image
- = virtual image

52
Q

What is plane polarisation

A

Plane polarisation is when the oscillations of a wave are restricted to a single plane.
They are oscillations of an electric field that only travel in one plane

53
Q

What condition is needed for polarisation to work

A

Needs to be with a transverse wave

54
Q

Explain the effect of two filters on the intensity of light, and why the intensity varies. The apparatus involves too polarising filters in between a sort of light and a light detector. The second filter is rotated.

A

Light from the source is unpolarised
Intensity is reduced to 1/2 by the first filter
At 0° and 180° filter two is aligned with filter one, so the intensity is at its greatest as all light passes through both filters - all the light in the same plane is transmitted
As filter two is rotated, only one component of light is allowed through
At 90°, all light is absorbed as filters are perpendicular to each other

55
Q

Explain the difference between polarised and unpolarised light

A

Polarised light is oscillations that can only travel in one plane
Unpolarised light travels in all directions
Polarised light travels with less intensity as half the components are cancelled out
Oscillations are perpendicular to the direction of propagation (transverse wave)

56
Q

Describe what is meant by a real image

A

Light rays converge to a point where the image is formed

57
Q

how does the refractive index affect refraction

A

When light enters a material with higher refractive index, the angle of refraction will be smaller than the angle of incidence and the light will be refracted towards the normal of the surface. The higher the refractive index, the closer to the normal direction the light will travel.
This is because when light travels from a fast medium to slower medium it will bend towards the normal. Therefore, if the change in speed is less then it will bend less away from the normal.

58
Q

how does the refractive index affect refraction

A

When light enters a material with higher refractive index, the angle of refraction will be smaller than the angle of incidence and the light will be refracted towards the normal of the surface. The higher the refractive index, the closer to the normal direction the light will travel.

59
Q

What is Huygens construction

A

The interference of wavelets to create the next wave front

60
Q

Define superposition of waves

A

2 or more waves meet
The displacement is the sum of the individual displacements from the individual waves

A Level Physics (6 decks)

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