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Alevel Physics (Edexcel) > Topic 5 > Flashcards

Topic 5 Flashcards

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1
Q

What is a wave’s amplitude?

A

The amplitude of a wave is its maximum displacement form 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 to peak or trough to trough)

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6
Q

State the equation used to calculate a wave’s speed

A

v=fλ

Speed = Frequency x 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 rarefractions (low pressure regions), and compressions (high pressure regions)

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8
Q

Decribe a transverse wave

A

Particle oscilations 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 progressivewave 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 that wave is. it is usually measured in radians, where a complete cycle is 2π

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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 happns 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 strign depend on?

A

Time period

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

Intensity = Power / 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

refractive index = speed of light / speed

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24
Q

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

A

n₁sinθ₁ = n₂sinθ₂

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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?

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

How do you calculate the total power of a combination of thin lenses?

A

P = P₁ + P₂ + P₃ + …

32
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

33
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

34
Q

State the equation used to calculate the magnification of an image

A

Magnification = Image Height / Object Height

35
Q

What is plane polarisation?

A

Plane polarisation is when the oscilations of a wave are restricted to a single plane.

36
Q

What is diffraction?

A

Diffraction is the spreading out of a wave as it passes through a gap

37
Q

What criteria must be met for maximum diffraction to occur?

A

The size of the gap must be of the same magnitude as the wavelength of the wave

38
Q

What happens if the gap is much smaller than the wavelength of the wave?

A

The wave will be reflected

39
Q

State the diffraction grating equation

A

nλ = dsinθ

40
Q

What does electron diffraction provide evidence for?

A

The wave nature of electrons. It suggests that particles can demostrate wavelike properties

41
Q

Describe the diffraction pattern produced by electrons

A

Concentric circles of bright and dark fringes from a central bright point

42
Q

If electrons didn’t have a wave nature, describe the pattern that would be produced when they pass through a slit.

A

The electrons would be unaffected by the gap and pass straight through. A single bright region would be formed

43
Q

What is the name given to the wavelength of a particle?

A

De Broglie wavelength

44
Q

What two factors does the de Broglie wavelength depend on?

A

Mass

Velocity

45
Q

State the equation used to calculate a de Broglie wavelength

A

λ = h/p

De Broglie Wavelength = Planck’s constant / momentum

46
Q

What is the basic process of a pulse-echo technique?

A

A wave pulse is emitted
It is transmitted and reflected at the boundary between two media
The returning wave (echo) is detected
The speed and time taken are used to calculate the distance to the object

47
Q

Suggest two things that may limit the amount of information that can be obtained by a pulse-echo technique

A

The wavelength of the radiation

The duration of the pulse

48
Q

What are the two models that can be used to describe electromagnetic radiation?

A

The wave model

The particle model

49
Q

Which model does the photoelectric effect provide evidence for?

A

The particle model

50
Q

Outline the photoelectric effect

A

Light is shone on a metal plate.
If the light has a high enough frequency, electrons are emitted from the metal surface
If the frequency is too low, no electrons are emitted

51
Q

What are the particles of light used to explain the photoelectric effect called?

A

Photons

52
Q

How do you calculate the energy of a photon?

A

E=hf

Energy = Planck’s constant x Frequency

53
Q

Explain how a photon can liberate an electron

A

One photon interacts with one electron and transfers all its energy to it. If this energy is greater than the metal’s work function, the electron will have sufficient energy to be released

54
Q

What is threshold frequency?

A

A metal’s threshold frequency is the minimum frequency that a photon requires to liberate an electron from its surface

55
Q

If the intensity of light being shone on a metal increases, how does the energy of the photoelectrons change?

A

The energy remains unaffected. An increase in intensity means more photons per area and so more photoelectrons are emitted

56
Q

Why are photoelectrons emitted with a range of kinetic energies?

A

The electrons are at different dephs in the metal and so require different amounts of energy to be liberated. The excess energy from a photon once an electron has been liberated, is the kenetic energy of the electron

57
Q

State the equation for the maximum kinetic energy of a photoelectron

A

1/2mv^2 = hf - Φ

Kinetic energy = planck’s constant x frequency - the metal’s work function

58
Q

What is the conversion factor between eV and J?

A

1eV = 1.6x10^-19J

59
Q

What happens when electrons transition between energy levels?

A

If electrons move to a higher energy level, radiation must be absorbed.
If electrons move to a lower energy level, radiation is emitted.

60
Q

Why can only certain frequencies of radiation be absorbed by an atom to cause an electron transition?

A

The electrons can only exist in discrete energy levels. The energy of the photon absorbed must be the exact amount of energy required to cover the difference between two discrete energy levels

Alevel Physics (Edexcel) (13 decks)

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