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A Level Physics > Electrons, Waves and Photons > Flashcards

Electrons, Waves and Photons Flashcards

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
Number density
Number density is the number of free charge carriers per unit volume
26
Current mean drift velocity equation
Anev | Cross sectional area x number density x elementary charge x mean drift velocity
27
The electron gun
This is a device that uses a large accelerating potential difference to produce a narrow beam of electrons
28
Internal resistance
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
29
Terminal p.d.
The potential difference measured at the terminals of the power source
30
Lost volts
The potential difference across the internal resistor of a source e.m.f
31
Electromotive force equations
Terminal p.d + current x internal resistance V + Ir I(R+ r) Current (resistance of the circuit + internal resistance)
32
Progressive wave
A progressive wave is an oscillation that travels through matter transferring energy from one place to another, but not transferring matter
33
Transverse waves
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
34
Longitudinal waves
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
35
Examples of longitudinal waves
Sound waves | P- waves produced in earthquakes
36
Displacement
Distance from the equilibrium position in a particular direction
37
Amplitude
Maximum displacement from the equilibrium position
38
Wavelength
Minimum distance between two points in phase on adjacent waves
39
Period of oscillation
The time taken for one oscillation of one wavelength to pass a given point
40
Frequency
The number of wavelengths passing a given point per unit time
41
Wave speed
The distance travelled by the wave per unit time
42
Frequency equation
=1 | Time
43
Wave equation
Wave speed = frequency x wavelength
44
Phase difference
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
Reflection
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
Law of reflection
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
Refraction
Refraction is the change in direction of a wave as it changes speed when it passes from one medium to another
48
What happens to the Wavelength and frequency of a wave in refraction
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
What happens to a wave changing medium as it slows down
It refracts towards the normal
50
What happens to a wave changing medium as it speeds up
It refracts away from the normal
51
Diffraction
This is the phenomenon in which waves passing through a gap or around an obstacle spread out
52
Polarisation
This is the phenomenon in which oscillations of a transverse wave are limited to only one plane
53
Refractive index
= c (speed of light through a vacuum 3.0x10^8) | v (speed of light through the material)
54
Partially polarised wave
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
Intensity equation and definition
Intensity of a progressive wave is the radiant power passing through a surface per unit area I=radiant power Cross sectional area
56
Intensity is directly proportional to
Amplitude ^2
57
The principle of superposition of waves
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
Interference
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
Constructive interference
Superposition of two waves in phase so that the resultant wave has a greater amplitude than the original waves
60
Destructive interference
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
Coherence
This refers to waves emitted from two sources having a constant phase difference
62
Path difference
This is the difference in the distance travelled by two waves from their source to a specific point
63
What does the Young double-slit experiment using visible light show
this experiment gave a classical confirmation of the wave-nature of light.
64
Properties of electromagnetic waves
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
Electromagnetic spectrum
Highest wavelength and lowest frequency first | Radio waves, Microwaves, Infrared waves, visible light, ultra violet light, x-rays, gamma rays
66
Critical angle equation
SinC= 1 | Refractive index
67
Stationary wave
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
How a stationary wave forms
They form when two progressive waves with the same frequency (and ideally the same amplitude) travelling in opposite directions are supposed
69
Nodes
A point where the amplitude is always zero
70
Antinodes
A point where the amplitude is always maximum
71
Photons
A quantum of electromagnetic energy
72
Energy of a photon equations
Frequency x Planks constant Planks constant x speed of light Wavelength
73
Photon model
Shows the particulate nature of electromagnetic radiation
74
Photoelectric effect
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
Photoelectrons
These are electrons emitted from the surface of a metal by the photoelectric effect
76
Work function
This is the minimum energy needed to remove a single electron from the surface of a particular metal
77
Threshold frequency
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
Einsteins photoelectric equation
hf = o + KEmax Energy = work function + maximum kinetic energy of the emitted electron
79
Wave- particle duality
This theory states that matter has both particle and wave properties
80
The de broglie equation
Wavelength = plank constant | Momentum
81
Describe a demonstration of the photoelectric effect
Gold leaf electroscope and zinc plate experiment
82
Antiphase
Particles oscillating completely out of step with each other
83
In phase
Particles oscillating perfectly in time with each other
84
Out of phase
Particles that are neither in phase, nor antiphase
85
Fundamental frequency
This is the lowest frequency at which an object can vibrate
86
The fundamental mode of vibration
This is a vibration at the fundamental frequency and is called the first harmonic
87
Harmonic
A harmonic is a whole number multiple of the fundamental frequency
88
Stationary wave patterns for air columns in tubes closed at one end
Anti-nodes at open end | Nose at the closed end
89
Stationary wave patterns for air columns in open tubes
Anti nodes at both open ends
90
Stationary wave patterns for air columns in a stretched spring
Node at each end fixed point | When plucked it vibrates in its fundamental mode of vibration
91
The separation between adjacent nodes (or antinodes)
Wavelength | 2

A Level Physics (5 decks)

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