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A Level Physics > Electrons, Waves and Photons > Flashcards

Electrons, Waves and Photons Flashcards

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1
Q

Electric current definition and equation

A

Rate of flow of charge
Charge = current
Time

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2
Q

What is the unit of charge

A

Coulombs

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3
Q

Elementary charge

A

1.6x10^-19

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4
Q

Electric charge

A

A physical property that all bodies possess, either positive or negative

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5
Q

Conventional current

A

This is from a positive terminal to a negative terminal

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6
Q

Electron flow

A

This is the electron current from a negative terminal to a positive terminal

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7
Q

Kirchhoff’s first law

A

At any point in a circuit, the sum of the currents into that point is equal to the sum of currents out of that point

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8
Q

Conservation of charge

A

This states that electric charge can neither be created nor destroyed

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9
Q

Kirchhoff’s second law

A

The conservation of energy. In any circuit the sum of the electromotive forces is equal to the sum of the potential differences around a closed loop

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10
Q

Energy transfer eV equation =

A

0.5 x mass x velocity^2

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11
Q

Electromotive force equation and definition

A

=energy transferred
Charge
This is used to describe when work is done on the charge carriers and the charges gain energy

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12
Q

Potential difference

A

This is defined as the energy transferred from electrical energy per unit charge
Also this is used to describe when work is done by the charge carriers and charges lose energy

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13
Q

Ohms Law

A

For a metallic conductor at constant temperature the potential difference across the conductor is directly proportional to the current

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14
Q

Resistance equation

A

Potential difference

Current

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15
Q

Resistance in a series

A

Rtotal = R1 +R2

The total resistance of two components is the sum of the resistance of each component

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16
Q

Resistance in Parallel

A

1/Rtotal = 1/R1 + 1/R2

The total resistance of two resistors is less than the resistance of the smallest individual resistor

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17
Q

Resistivity of a material equation

A

Resistance = resistivity x length

cross sectional area

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18
Q

3 factors that determine and affect the resistance of the wire

A

Material
Length- resistance of a wire is directly proportional to its length
Cross sectional area- resistance of a wire is inversely proportional to its cross sectional area

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19
Q

Potential divider

A

An electrical circuit designed to divide the potential difference across two or more components (often two resistors) in order to produce a specific output

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20
Q

Potentiometer

A

This is an electrical component with 3 terminals and some form of sliding contact that can be adjusted to vary the p.d between 2 of the terminals

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21
Q

Potential dividers equations

A

Vout = R2 x Vin
R1+R2

V1 = R1
V2 R2

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22
Q

Electrical power definition and equations

A 
The rate of energy transfer by each electrical component 
=current x potential difference 
=current^2 x resistance 
= potential difference^2
    Resistance
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23
Q

Energy transferred and the unit

A

Potential difference x current x time

The kilowatt-hour (kWh) is a unit of energy

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24
Q

Mean drift velocity

A

This is the average velocity of electrons as they move through a wire

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25
Q

Number density

A

Number density is the number of free charge carriers per unit volume

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26
Q

Current mean drift velocity equation

A

Anev

Cross sectional area x number density x elementary charge x mean drift velocity

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27
Q

The electron gun

A

This is a device that uses a large accelerating potential difference to produce a narrow beam of electrons

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28
Q

Internal resistance

A

The resistance of a source of e.m.f due to its construction which causes a loss in energy/voltage as the charge passes through the source

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29
Q

Terminal p.d.

A

The potential difference measured at the terminals of the power source

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30
Q

Lost volts

A

The potential difference across the internal resistor of a source e.m.f

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31
Q

Electromotive force equations

A

Terminal p.d + current x internal resistance
V + Ir
I(R+ r)
Current (resistance of the circuit + internal resistance)

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32
Q

Progressive wave

A

A progressive wave is an oscillation that travels through matter transferring energy from one place to another, but not transferring matter

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33
Q

Transverse waves

A

A wave in which the medium is displaced perpendicular to the direction of energy transfer and oscillations of the medium particles are perpendicular to the direction of wave travel

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34
Q

Longitudinal waves

A

A wave in which the medium is displaced in the same line as the direction of energy transfer and oscillations of the medium particles are parallel to the direction of wave travel

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35
Q

Examples of longitudinal waves

A

Sound waves

P- waves produced in earthquakes

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36
Q

Displacement

A

Distance from the equilibrium position in a particular direction

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37
Q

Amplitude

A

Maximum displacement from the equilibrium position

38
Q

Wavelength

A

Minimum distance between two points in phase on adjacent waves

39
Q

Period of oscillation

A

The time taken for one oscillation of one wavelength to pass a given point

40
Q

Frequency

A

The number of wavelengths passing a given point per unit time

41
Q

Wave speed

A

The distance travelled by the wave per unit time

42
Q

Frequency equation

A

=1

Time

43
Q

Wave equation

A

Wave speed = frequency x wavelength

44
Q

Phase difference

A

Phase difference is the difference in displacement along a wave or in 2 different waves, measured in degrees or radians, with each complete cycle or a difference of one wavelength representing 360 degrees or 2pie radians

45
Q

Reflection

A

This is the change in direction of a wave at a boundary between two different media so that the wave remains in the original medium

46
Q

Law of reflection

A

The law of reflection states that the angle of incidence is equal to the angle of reflection.
When waves are reflected their wavelength and frequency do not change

47
Q

Refraction

A

Refraction is the change in direction of a wave as it changes speed when it passes from one medium to another

48
Q

What happens to the Wavelength and frequency of a wave in refraction

A

Frequency does not change but the wavelength does
If the wave slows down the wavelength decreases
If the wave speeds up the wavelength increases

49
Q

What happens to a wave changing medium as it slows down

A

It refracts towards the normal

50
Q

What happens to a wave changing medium as it speeds up

A

It refracts away from the normal

51
Q

Diffraction

A

This is the phenomenon in which waves passing through a gap or around an obstacle spread out

52
Q

Polarisation

A

This is the phenomenon in which oscillations of a transverse wave are limited to only one plane

53
Q

Refractive index

A

= c (speed of light through a vacuum 3.0x10^8)

v (speed of light through the material)

54
Q

Partially polarised wave

A

This is a transverse wave in which there are more oscillations in one particular but the wave is not completely plane polarised and it occurs when transverse waves reflect off a surface

55
Q

Intensity equation and definition

A

Intensity of a progressive wave is the radiant power passing through a surface per unit area
I=radiant power
Cross sectional area

56
Q

Intensity is directly proportional to

A

Amplitude ^2

57
Q

The principle of superposition of waves

A

This states that when two waves meet at a point the resultant displacement at that point is equal to the sum of the displacements of the individual waves

58
Q

Interference

A

This is the superposition of two progressive waves from coherent sources to produce a resultant wave with a displacement equal to the sum of the individual displacements from the two waves

59
Q

Constructive interference

A

Superposition of two waves in phase so that the resultant wave has a greater amplitude than the original waves

60
Q

Destructive interference

A

Superposition of two waves in anti phase so that the waves cancel each other out and the resultant wave has smaller amplitude than the original waves

61
Q

Coherence

A

This refers to waves emitted from two sources having a constant phase difference

62
Q

Path difference

A

This is the difference in the distance travelled by two waves from their source to a specific point

63
Q

What does the Young double-slit experiment using visible light show

A

this experiment gave a classical confirmation of the wave-nature of light.

64
Q

Properties of electromagnetic waves

A

Transverse waves
Do not need a medium to propagate
Travel at the speed of light in a vacuum
They have oscillating magnetic and electric field components

65
Q

Electromagnetic spectrum

A

Highest wavelength and lowest frequency first

Radio waves, Microwaves, Infrared waves, visible light, ultra violet light, x-rays, gamma rays

66
Q

Critical angle equation

A

SinC= 1

Refractive index

67
Q

Stationary wave

A

A stationary (standing) wave is a wave that remains in constant position with no net transfer of energy and is characterised by its nodes and anti nodes.

68
Q

How a stationary wave forms

A

They form when two progressive waves with the same frequency (and ideally the same amplitude) travelling in opposite directions are supposed

69
Q

Nodes

A

A point where the amplitude is always zero

70
Q

Antinodes

A

A point where the amplitude is always maximum

71
Q

Photons

A

A quantum of electromagnetic energy

72
Q

Energy of a photon equations

A

Frequency x Planks constant

Planks constant x speed of light
Wavelength

73
Q

Photon model

A

Shows the particulate nature of electromagnetic radiation

74
Q

Photoelectric effect

A

The photoelectric effect is the emission of photoelectrons from a metal surface when electromagnetic radiation above a threshold frequency is incident on the metal

75
Q

Photoelectrons

A

These are electrons emitted from the surface of a metal by the photoelectric effect

76
Q

Work function

A

This is the minimum energy needed to remove a single electron from the surface of a particular metal

77
Q

Threshold frequency

A

This is the minimum frequency of the electromagnetic radiation that will cause the emission of an electron from the surface of a particular metal

78
Q

Einsteins photoelectric equation

A

hf = o + KEmax

Energy = work function + maximum kinetic energy of the emitted electron

79
Q

Wave- particle duality

A

This theory states that matter has both particle and wave properties

80
Q

The de broglie equation

A

Wavelength = plank constant

Momentum

81
Q

Describe a demonstration of the photoelectric effect

A

Gold leaf electroscope and zinc plate experiment

82
Q

Antiphase

A

Particles oscillating completely out of step with each other

83
Q

In phase

A

Particles oscillating perfectly in time with each other

84
Q

Out of phase

A

Particles that are neither in phase, nor antiphase

85
Q

Fundamental frequency

A

This is the lowest frequency at which an object can vibrate

86
Q

The fundamental mode of vibration

A

This is a vibration at the fundamental frequency and is called the first harmonic

87
Q

Harmonic

A

A harmonic is a whole number multiple of the fundamental frequency

88
Q

Stationary wave patterns for air columns in tubes closed at one end

A

Anti-nodes at open end

Nose at the closed end

89
Q

Stationary wave patterns for air columns in open tubes

A

Anti nodes at both open ends

90
Q

Stationary wave patterns for air columns in a stretched spring

A

Node at each end fixed point

When plucked it vibrates in its fundamental mode of vibration

91
Q

The separation between adjacent nodes (or antinodes)

A

Wavelength

2

A Level Physics (5 decks)

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