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Physics (OCR B) > Key Defintions > Flashcards

Key Defintions Flashcards

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1
Q

Precise

A

Multiple measurements with the same or very similar results.

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2
Q

Accurate

A

How close a measurement is to the true value.

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3
Q

Systematic Error (what is it)

A

An error of measurement due to readings that systematically differ from the actual value (follow a pattern, trend or bias)

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4
Q

Systematic Error (defining features)

A

Poor accuracy
Definite causes
Reproducable
Cannot be eliminated with a mean

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5
Q

Random Error (what is it)

A

An error of measurement due to readings that vary randomly (or have an outlier) with no recognisable pattern, trend or bias.

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6
Q

Random Error (defining features)

A

Poor precision
Nonspecific causes
Not reproducable
Can be reduced by calculating a mean.

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7
Q

Elastic Behaviour

A

Deforms when force is applied, returns to original shape when force removed

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8
Q

Plastic Behaviour

A

Deforms when force is applied, does not return to original shape when force removed

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9
Q

Brittle

A

Breaks through cracks/fracture propagation (little/none plastic deformation)

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10
Q

Ductile

A

Undergoes plastic deformation under tensile forces

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11
Q

Malleable

A

Undergoes plastic deformation under compressive forces

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12
Q

Tough

A

Can absorb a lot of energy (by plastic deformation) before breaking

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13
Q

Hard

A

Resistance to scratching

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14
Q

Stiff

A

Requires lots of force for a little amount of deformation

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15
Q

Strong

A

Requires large forces to break

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16
Q

Hooke’s Law

A

For a material behaving elastically, the extension/compression is proportional to the force applied

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17
Q

Ionic Bonds

A

Strong bonds formed by the transfer of electrons between atoms

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18
Q

Covalent Bonds

A

Bonds that hold atoms together in molecules, formed by the sharing of electrons.

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19
Q

Metallic Bonds

A

Some electrons loosely held and not tied to particular atoms.
A metal is effectively made up of +ve ions in a sea of -ve electrons.

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20
Q

Hydrogen Bonds

A

Weak bonds which hold together adjacent molecules (such as water) through electrostatic attraction between the slightly +ve oxygen and slightly -ve hydrogen of adjacent molecules

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21
Q

Crystalline

A

Atoms bonded w/ a regular arrangement extending in all three spatial directions

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22
Q

Polycrystalline

A

Made up of many interlocking crystals
Atoms bonded in a ‘regular’ structure
Boundaries between separate interlocking grains

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23
Q

Amorphus

A

Atoms bonded w/out irregular structure
Has regions of weakness, brittle

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24
Q

Toughness

A

Can be indicated by the energy absorbed before breaking, per unit cross-sectional area

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25
Q

1D defect

A

Point Defect

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26
Q

Types of defect (1D)

A

Vacancy
Interstatial Impurity
Substitution Impurity

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27
Q

2D defect

A

Line Deformity

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28
Q

Types of defect (2D)

A

Edge Dislocation

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29
Q

Line defects often ____ under stress due to _____. This leads to ___ and will continue until ___.

A

Migrate
Breaking and reforming of bonds
The plastic flow of deformations
The line defects reach the grain boundary and build up

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30
Q

Charge Carrier Density

A

The number of free conduction electrons per m^3 of material
m-^3

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31
Q

Charge Carrier Density of an Insulator

A

approx. 10^7 m^-3

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32
Q

Charge Carrier Density of a Conductor

A

approx. 10^28 m^-3

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33
Q

Semi-Conductor

A

materials who’s conductivity changes depending on outside conditions

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34
Q

Metal

A

Consists of a single element or a blend of elements (alloy)

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35
Q

Metal properties

A

Tend to be good conductors (heat + elec)
Tend to be strong, stiff and tough
Generally hard, malleable and ductile

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36
Q

Ceramic

A

Chemical compound (often oxides or nitrates)
Often formed by mixing a starting material with water, shaping and then firing to harden

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37
Q

Ceramic Properties

A

Generally inert with high melting points
Generally very strong and stiff
Usually hard and brittle

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38
Q

Polymer (Definition + general property)

A

Organic compound made of long chain molecules
Typically strong and flexible

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39
Q

Thermoplastics (Polymer)

A

Easily moulded into desired shape when warm (can be remelted and shaped)

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40
Q

Thermosets (Polymer)

A

Hard and brittle, difficult to shape after polymerisation (even if heated)

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41
Q

Composites

A

Combine desirable properties of different component materials

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42
Q

Limit of Proportionality

A

Up until this point a material behaves as a regular elastic solid

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43
Q

Yield Point

A

Denotes the onset of plastic deformation

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44
Q

Yield Strength

A

The stress at which an object starts to plastically deform. This is at the Yield Point

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45
Q

Wavelength of Gamma Radiation

A

Less than 1 pm
Less than 1*10^-12 m

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46
Q

Wavelength of X-Rays

A

Between 1 pm and 1 nm
Between 1 *10^-12 m and 1 *10^-9 m

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47
Q

Wavelength of UV

A

Between 1 nm and 400 nm
Between 1 *10^-9 m and 400 *10^-9 m

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48
Q

Wavelength of Visible

A

Between 400 nm (purple) and 750 nm (red)
Between 400 *10^-9 m and 750 *10^-9 m

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49
Q

Wavelength of Infrared

A

Between 750 nm and 2.5 μm
Between 750 *10^-9 m and 2.5 *10^-6 m

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50
Q

Wavelength of Near Infrared

A

Between 2.5 μm and 25 μm
Between 2.5 *10^-6 m and 25 *10^-6 m

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51
Q

Wavelength of Microwave

A

Between 25 μm and 1 mm
Between 25 *10^-6 m and 1 *10^-3 m

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52
Q

Wavelength of Radiowave

A

Greater than 1 mm
Greater than 1*10^-3 m

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53
Q

Wavefronts after focussing are ____.

A

Curved
n.b. lenses add constant curvature

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54
Q

Lens Power

A

The curvature a lens adds to the wavefronts, measured in dioptres (D)

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55
Q

Focal length =

A

Radius of Curvature (r)

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56
Q

Convex Lens w/ a very distant object

A

Image at focal point

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57
Q

Convex Lens w/ object beyond focal point

A

Image visible (no specific place, depends on distance)

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58
Q

Convex Lens w/ object at focal point

A

Very distant image

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59
Q

Convex lens, object > 2f

A

Image -
Real
Inverted
Smaller than object

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60
Q

Convex lens, f < object < 2f

A

Image -
Real
Inverted
Larger than object

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61
Q

Convex lens, object = 2f

A

Image -
Real
Inverted
Same Size

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62
Q

Convex lens, object < f

A

Image -
Virtual
Upright
Larger than object

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63
Q

Smoothing an Image

A

Apply a mean filter to each pixel
(replace each pixel by the mean of it and its 8 neighbours)

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64
Q

Noise

A

False/Random data in an image caused by interferance
Removed using a median filter

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65
Q

Improving Brightness

A

Add/Subtract a constant value from each pixel

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66
Q

Improving Contrast

A

Multiply by a particular factor
You want the pixel values to be spread across the whole range (light becomes lighter, dark becomes darker)

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67
Q

Edge detection (Laplace Rule)

A

Enhances edges in an image (highlight regions with an abrupt change of brightness)
Subtract the N, E , S and W vals from 4 * the pixel val
If no edge but is a gradient, it simply smooths

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68
Q

Transverse wave

A

Oscillations are perpendicular to the direction of the wave

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69
Q

Polarised Light

A

The wave only oscillates in one particular direction. Produced by polarising filters or reflection and is made of EM waves

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70
Q

A grill is aligned perpendicular to a polarised wave

A

Little to no energy loss (before grill vs after)

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71
Q

A grill is aligned at 45° to a polarised wave

A

Some energy lost

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72
Q

A grill is aligned parallel to a polarised wave

A

Most/All energy lost

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73
Q

What happens when light reflects off a surface at a suitable angle?

A

The oscillations of the electric fields become restricted to a direction parallel to the plane of the surface.

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74
Q

Unpolarised light

A

Has oscillations in many directions. Is produced by the Sun and most lightbulbs and is made of EM waves

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75
Q

Analogue signal

A

Continuous signals that can have any value between a maximum and a minimum. Likely to pick up noise which affects signal quality

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76
Q

Attenuation

A

A gradual loss of intensity (or amplitude) of a signal

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77
Q

Digital signal

A

Has only two values, 0 and 1. Due to this, if noise is picked up, the signal quality is not affected. They can be changed/scrambled/interrupted significantly easier than analogue.

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78
Q

Nyquist Theorem

A

For a signal to be represented well:
Sampling Frequency > 2 * smallest important freq change
Sampling Frequency > 2 * highest freq

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79
Q

Levelling

A

The conversion of an analogue signal to a digital signal through sampling

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80
Q

Shannon’s Criteria

A

A formula to find the number of bits per sample required to adequately translate Analogue -> Digital

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81
Q

Transmission Rate

A

The amount of information sent per second

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82
Q

Electric Current

A

‘rate of flow of charge’
the amount of charge passing a certain point in the circuit each second

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83
Q

Coulumb

A

‘The total charge passing a point when a current of 1 Amp flows for a time of 1 second’

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84
Q

Ammeters

A

Measure the amount of charge flowing through a point in a circuit each second. Must be in series.

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85
Q

Voltmeter

A

Compares the energy of charge carriers before and after the component. Must be in parallel.

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86
Q

Resistance

A

The opposition to current for a given p.d.

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87
Q

Ohms Law

A

For a fixed resistor at a constant temperature, the current through the resistor is directly proportional to the p.d. across it.

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88
Q

Conductance

A

The inverse of Resistance

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89
Q

Kirchoff’s First Law

A

The total current entering a junction is equal to the sum of currents leaving the junction

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90
Q

Rheostat

A

Electrical instrument used to control a current by varying the resistance

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91
Q

Diode

A

Unidirectional component. Large amounts of current can only flow in one direction (eg A to B). Little/no current can flow in the other direction (eg B to A)

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92
Q

Thermistor

A

A resistor which resistance changes depending on the temperature it is at.

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93
Q

Thermistor - PTC

A

as temp increases, resistance increases

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94
Q

Thermistor - NTC

A

as temp increases, resistance decreases

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95
Q

Competing effects in a thermistor

A

Heat up causes greater lattice ion vibrations - resistance up
Heat up releases more electrons, so more current - resistance down

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96
Q

LDR - light dependant resistor

A

High resistance in standard conditions. When illuminated, electrons are released - resistance down

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97
Q

Calibrated

A

Correlating the readings of an instrument with known readings in order to check accuracy of instrument

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98
Q

Response Time

A

The time it takes for a sensor to respond to a change in outside conditions

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99
Q

Sensitivity

A

The change in reading on the instrument per unit change in outside condition

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100
Q

Resolution

A

The smallest change an instrument can detect

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101
Q

Electromotive Force (EMF)

A

Energy per unit charge transferred into the circuit at the power supply. ε
Energy gained per unit charge by the charge carriers in a circuit

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102
Q

Internal resistance

A

The resistance of the power supply.
Treated as an extra resistor in series with the external circuit

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103
Q

Terminal p.d.

A

The sum of the p.d. of all the load resistors. Always less than EMF because of internal resistance (not included in ‘load’ resistors)

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104
Q

Longitudional

A

The oscillations are parallel to the direction of motion

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105
Q

Amplitude

A

Maximum displacement of a wave

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106
Q

Frequency

A

The number of oscillations that occur each second

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107
Q

Displacement (wave)

A

Distance of a point on a wave from its position of equilibrium

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108
Q

Compression (wave)

A

Lots of particles in a set area

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109
Q

Rarefaction

A

Very few particles in a set area

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110
Q

Wave Speed

A

The speed at which energy is transmitted by a wave
The speed at which a wave front propagates

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111
Q

Coherent

A

Two waves with the same frequency, same wavelength and a constant phase relationship

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112
Q

Superposition

A

Two waves meeting and combining. Their displacements add together

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113
Q

Constructive Superposition (coherent)

A

When two coherant waves meet and combine (and are in phase), the displacements add together.
(a +ve displacement plus a +ve displacement or -ve plus -ve)

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114
Q

Destructive Superposition (coherent)

A

When two coherent waves meet and combine (and are antiphase) the displacements subtract.
(a -ve displacement plus a +ve displacement or +ve plus -ve)

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115
Q

Incoherent waves or not antiphase waves superposing

A

Can get very complex as can end up with a mix of constructive or destructive

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116
Q

When does a standing wave form

A

When two progressive waves of the same frequency and wavelength travel in opposite directions and superpose

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117
Q

Node (standing wave)

A

A place where the waves always meet in antiphase (undergo destructive superposition). They are always stationary on the middle line

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118
Q

Antinode (standing wave)

A

A place where the waves always meet in phase (undergo constructive superposition). They are always at the same point but can be max +ve or max -ve (two different wave forms)

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119
Q

Phase difference

A

The difference in phase (or angular difference) between two points on a wave (or the same point on two waves)

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120
Q

In phase

A

One complete cycle apart (0° or a multiple of 360°)
Can be written in radians

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121
Q

Antiphase

A

A half cycle out of phase (a multiple of 180° excluding multiples of 360°)

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122
Q

Out of Phase

A

Not in phase or antiphase.

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123
Q

Diffraction

A

The spreading out of a wave into a ‘shadow region’ as the wave travels through a gap or past a barrier

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124
Q

When does the greatest diffraction occur

A

When the gap/barrier is the same as the wavelength of the incident wave

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125
Q

Interference

A

Occurs when waves overlap and their resultant displacement is the sum of the displacement of each wave. Often occurs after diffraction

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126
Q

What colour of light diffracts the most/least?

A

Red diffracts most and violet the least as red has a longer wavelength

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127
Q

What happens when white light is diffracted

A

Different wavelengths of light separate out as they are diffracted different amounts

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128
Q

Single slit diffraction

A

Produces a fringe pattern, central fringe is much brighter + 2x the width of the other fringes

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129
Q

Double slit diffraction

A

Fringe intensity is max at n = 0
The intensity decreases symmetrically as n increases
All fringes are a uniform thickness

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130
Q

Diffraction grating diffraction

A

Fringes have a similar intensity
Fringes are symmetrical about n = 0
Fringe width < distance between fringes
Fringes equally spaced

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131
Q

Total Internal Reflection

A

Occurs when the angle of incidence exceeds the critical angle

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132
Q

Path length

A

The difference between a wave source and a point in space
Often measured in multiples of λ

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133
Q

Path difference

A

The difference in path lengths between two sources to the same point.

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134
Q

What happens when a wave is transmitted from low - > high density medium

A

Wave speed decreases
Wave length decreases
Frequency remains constant

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135
Q

Refraction

A

The bending of light as it hits a boundary between two media of different optical densities at an angle

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136
Q

Refractive Index

A

The ratio of the speed of light in the first medium to the speed of the wave in the second medium

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137
Q

Absolute refractive index

A

The ratio of speed of light in air (or a vacuum) to the speed of light in the medium

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138
Q

Charge carried by one electron

A

1.6 * 10^-19 C

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139
Q

Electrons in 1 C of charge

A

6.3 * 10^18 electrons

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140
Q

Capacitor

A

Stores charge (and therefore pd) on parallel conductive plates, separated by an insulating layer (dielectric)

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141
Q

Radioactive decay is ___

A

Random
Exponential
Spontanious

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142
Q

Radioactive decay (Spontaneous)

A

Is not affected by external conditions

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143
Q

Radioactive decay (Exponential)

A

The rate of decay is proportional to the number of radioactive (parent) isotopes present

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144
Q

Radioactive decay (Random)

A

Can’t predict exactly when each nucleus will decay
Can give a probability it will decay in a fixed time interval

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145
Q

The photoelectric effect

A

The emission of electrons from the surface of a material due to the exposure of a material to EM radiation

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146
Q

Threshold Frequency

A

The minimum frequency of the EM required for a specific material to undergo the photoelectric effect.

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147
Q

Intensity and the photoelectric effect

A

Once the threshold frequency has been reached, the higher the intensity the more electrons are released from the surface of the material

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148
Q

Frequency and the photoelectric effect

A

Once the threshold frequency has been reached, the higher the frequency the higher the maximum KE of the emitted electrons.

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149
Q

Key Problems with Wave Theory (photoelectric effect)

A

Threshold Frequency - All frequencies should have eventually caused emission (but didn’t)
Increase in Intensity - Should have increased emissions for all frequencies, not just those above threshold
The metal should not have immediately released electrons, it should have taken time (esp on lower frequencies)

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150
Q

Photon

A

A quanta of light

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151
Q

Intensity

A

energy arriving per m^2 of area per second

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152
Q

Intensity is proportional to

A

Number of photons arriving each second - as a particle
Amplitude^2 - as a wave

153
Q

An increase of intensity (photoelectric effect)

A

Increases the number of photons each second - increases the number of photoelectrons leaving the metal each second (if above threshold freq)

154
Q

Work Function, Φ

A

The minimum energy required to release an electron from the surface of a metal (y-intercept)

155
Q

Planck’s constant

A

Used to calculate the energy of a photon (can be found using the gradient of a KE (eV) and frequency graph)

156
Q

How do LED’s work

A

Photons are released when electrons cross the p-n junction to fill layers in the p type layer. The plastic shell covering the LED directs the photons outwards.

157
Q

N-type layer

A

The impurities mean that there is a surplus of electrons

158
Q

P-type layer

A

The impurities mean that there is a deficit of electrons

159
Q

Striking voltage

A

The minimum voltage required to have electrons flow of across the p-n junction. Also related to the wavelength of the photon emitted as the electron drops back to ground state when it passes through the p-n junction

160
Q

Ground state

A

When an electron is in its lowest possible energy level

161
Q

Excited state

A

When an electron is at a higher energy level than its ground state - happens to outermost electron first

162
Q

How do electrons move between energy levels

A

Absorbing/emitting the energy from a single photon

163
Q

Emission Spectra

A

A representation of the different discrete photon energies emitted when the electrons of an element drop down from an excited state

164
Q

Absorption Spectra

A

A representation of the different discrete photon energies absorbed by the electrons in an element (they become excited)

165
Q

Diffraction inside a material

A

Will occur when electron waves have a similar wavelength to the spacing between atoms in a material

166
Q

de Broglie equations

A

Link wave behaviour and particle behaviour

167
Q

Resultant force

A

The sum of all the forces acting on the body

168
Q

Newton’s First Law

A

“An object at rest remains at rest and an object in motion remains at a constant velocity unless a resultant force acts”
INTERTIA

169
Q

Newton’s Second Law

A

“The acceleration of an object is directly proportional to the magnitude of the resultant force (in the same direction) and inversely proportional to the mass of the object”
F = ma

170
Q

Newton’s Third Law

A

“If body A exerts a force on body B, then body B exerts an equal size force in the opposite direction on body A”

171
Q

Newton’s Third Law 5 Key Rules

A

Same type of force
Same magnitude
Act along the same line of motion
Act in opposite directions
Act on two different bodies

172
Q

Ideal collision

A

Momentum is conserved - provided no external resultant force acts

173
Q

Elastic collision

A

All KE is conserved

174
Q

Inelastic collision

A

KE is not conserved, momentum is

175
Q

The Law of Conservation of Momentum

A

“The total momentum of a system before an interaction is the same as the total momentum after”

176
Q

Work done

A

The energy transferred to or from an object via the application of a force along a displacement

177
Q

Electron Diffraction (not observed)

A

They form diffraction patterns as they are behaving as a wave (wave function). As the electron can theoretically take any path to get to its destination, diffraction patterns are seen. The high probability areas form bright fringes and low probability areas form the gaps between.

178
Q

Electron Diffraction (observed)

A

Observation collapses the wave function, and the electrons behave as particles. They can only accept one probability, and particle like behaviour is the most likely.

179
Q

Scalar

A

Has a magnitude but no direction

180
Q

SHM

A

Simple Harmonic Motion is when a body oscillates about a fixed point (equilibrium).

181
Q

Ideal SHM

A

The periodic time is constant

182
Q

When does SHM occur

A

When a body is oscillating about a fixed point (equilbrium)
A restoring force must always act on the body towards equilibrium. The size of the restoring force is proportional to the displacement from equilibrium.

183
Q

Damping

A

A decrease in the amplitude of oscillations due to a loss of energy to the surroundings.

184
Q

The amplitude decreases due to damping is _____, because ____

A

Exponential
The amplitude decreases by the same factor (or ratio) with each successive cycle.

185
Q

Energy can be lost by _____. (SHM)

A

Hysteresis of elastic
Plastic deformation of materials
Friction/Air-resisitance

186
Q

Free Oscilation

A

No external force acting on the system (aside from the intial force)

187
Q

Forced Oscillation

A

Oscillations affected by a periodic driving force from outside the system

188
Q

Natural Frequency

A

The frequency at which a system oscillates when no external forces act

189
Q

Resonate

A

An increase of amplitude which occurs when the frequency of the driving oscillator is similar to the natural frequency of the oscillator

190
Q

Damped forced oscillations

A

Max amplitude of the forced oscillations decreases
The frequency at which the max amplitude occurs decreases
The peak gets less sharp and wider

191
Q

Ground resonance

A

When rotating or oscillating machines are in contact with the ground and improperly damped, they can resonate and oscillate dangerously. This can destroy the oscillator and the machine it is attached to.

192
Q

Base Isolation Systems

A

Used to damp earthquake oscillations. Decoupling the building from the ground using deformable dampers or ball bearings. This means the ground vibrations are inefficiently transmitted to the building

193
Q

Centripetal force

A

A resultant force acting towards the centre of a circle, causing the object to accelerate towards the centre of the circle. Acts at a right angle to the path of the circles motion. Not a ‘true’ force, caused by another identifiable pheonomenon.

194
Q

A field

A

A region of space where a force acts on an object

195
Q

A gravitational field

A

A region in space where a gravitational force acts on an object with mass

196
Q

Gravitational field strength, g

A

The force acting per unit mass.
Multiply by mass to get Force in a gravitational field, F
The area under the graph of it against r will give gravitational potential, Vg

197
Q

Gravitational Potential, GP

A

The work done in moving a unit mass from infinity to a point in the field
Multiply by mass to give GPE, Eg
The gradient at a point of a graph of it against r will give gravitational field strength, g

198
Q

Gravitational Potential Energy, GPE

A

The work done in moving an object from infinity to a point in a field
Divide by mass to give GP, Vg
The area under of a graph of it against r gives the Force, F

199
Q

Force, F (gravitational fields)

A

The force between two point masses
Divide by mass to give gravitational field strength, g
The gradient at a point of it against r will give gravitational potential energy, GPE

200
Q

The direction of the gravitational force is ______.

A

Opposite to the direction of the displacement as gravity is an attractive force

201
Q

Kepler’s Laws (1)

A

All planets have an elliptical orbit, with their star at one focus of the elipse

202
Q

Kepler’s Laws (2)

A

A line joining the planet to the sun sweeps out equal areas in equal times

203
Q

Kepler’s Laws (3)

A

The period of orbit is related to the average distance from the star.
T^2 α r^3

204
Q

Escape Velocity

A

The speed at which an object must be travelling to overcome the gravitational attraction of a planet. Found by the area between the curve and the axis on a g-r graph.
Object KE > GPE at surface (or point in field)

205
Q

Equipotentials

A

A line joining all points in space w/ an equal gravitational potential

206
Q

Polar Orbiting

A

Orbits in a N-S direction
Orbit takes ~2hrs
Can view many swathes of the Earth as it rotates
Often used for things like weather

207
Q

Geostationary Orbit

A

One orbit in 24 hr
Satellites remain above the same point on Earth at all times
Almost always equatorial
Used for things like GPS

208
Q

RADAR

A

RAdio Detection And Ranging
Uses EM waves to measure the distance to an object

209
Q

World Line

A

A line plotted onto a space-time diagram (shows how an object’s displacement varies with time)

210
Q

Doppler effect

A

The apparent change in wavelength or frequency of a wave when the source moves relative to the observer

211
Q

Doppler effect - towards the observer

A

The frequency appears to increase and the wavelength appears to shorten

212
Q

Doppler effect - away from the observer

A

The frequency appears to decrease and the wavelength appears to lengthen

213
Q

Paralax

A

The apparent change in position of an object relative to a fixed background when viewed from a different angle - can be used to approximate distances to nearby stars

214
Q

1 AU

A

The mean distance between the Earth and the Sun (1.496 * 10^11 m)

215
Q

Disadvantages of Parallax

A

Parallax angles are VV small
Due to the resolution of modern instruments, we can only use it on nearby stars

216
Q

Parsecs (pc)

A

The distance to a point in space where the parallax angle is 1 arc-second (3.09 * 10^16 m)

217
Q

Standard Candles

A

Objects of a known luminosity

218
Q

Cepheid Variables

A

The luminosity of these stars vary periodically (the period is directly related to the luminosity). This means we can use distant Cepheid Variables to estimate distances to far away galaxies (using its period to estimate its luminosity and then use that to estimate distance)

219
Q

Supernovea

A

Exploding stars that form when as star runs out of fuel for fusion, contracts and then explodes

220
Q

Aether

A

The medium it used to be believed that light travelled through.

221
Q

Einstein’s First Postulate

A

The laws of physics are the same in all inertial frames of reference

222
Q

Einstein’s Second Postulate

A

The speed of light is constant, regardless of the relative motion of the source and observer.

223
Q

Time Dilation

A

The concept that time is observed differently for objects with differing relative motion (eg stationary vs moving)

224
Q

Why does time dilation occur

A

Because the speed of light cannot vary, the time it takes for the light to cover a distance must APPEAR to change. Time in the ‘slower’ perspective moves slower

225
Q

The Lorentz Factor

A

The faster an object moves through the space, the slower it moves through time
Used to calculate relativistic effects

226
Q

Length Contraction

A

Where distance is measured differently the faster an object is going.
The faster it goes, the smaller the length

227
Q

Logarithmic Scale

A

Increases by a common multiple not by a common value.
- Encompasses a wide range of values
- Difficult to interpolate between scale markers
- Negative values and 0 cannot be represented

228
Q

Cosmological Redshift

A

Galaxies aren’t moving away from us, the space between is expanding (stretching)
This stretches the wavelength

229
Q

Key Assumption for Hubble’s Constant

A

That the recessional velocity of the galaxy has been constant all throughout history

230
Q

CMBR (four key points)

A

Cosmic Microwave Background Radiation
-Radiation sourced from deep space
-Part of the Big Bang
-Comes from the universe itself (not any objects w/in), sources from behind the stars
-Is microwave by the time it reaches Earth

231
Q

Era of Recombinition

A

The plasma of the early universe cooled down enough for electrons and protons to form atoms of hydrogen.
CMBR was released at this point (λ = 1mm)- the universe became transparent
300,000 yrs after the Big Bang
Temp is 3000K

232
Q

What is CMBR evidence of?

A

That the universe was once much hotter
The universe is 1000x bigger than it used to be
The early structure of the universe was very uniform w/ only very slight temp + density variations

233
Q

Specific Heat Capacity

A

The energy required to increase the temperature of 1kg of a substance by 1K

234
Q

Conduction

A

Kinetic Energy (vibrations) of atoms are passed to adjacent atoms, transferring energy through a solid

235
Q

Radiation

A

The transmission of heat from waves resulting from disturbances in a particle’s electric field as it vibrates

236
Q

A good conductor

A

Has lots of conduction electrons which are able to efficiently move through the solid and transfer energy when they collide with metal atoms

237
Q

The amount of radiation emitted depends on? (Heat)

A

Temperature (KE of particles)
- 0K = 0 vibrations = 0 radiation
Surface Area of an object
Type of surface
- Dull/Dark are good emitters + absorbers
- Shiny are bad emitters + absorbers

238
Q

How does temperature affect the nature of the radiation emitted? (Heat)

A

The higher the temp, the greater the amount (intensity) of radiation and the higher the frequency of the radiation emitted (VV hot objects glow)

239
Q

Convection

A

The transfer of heat energy by the motion of fluids (liquids/gases) due to difference in density. Can be gravity or pressure driven

240
Q

Pressure (gas)

A

Caused by the molecules colliding with the sides of their container

241
Q

The Kinetic Theory of Gases (4 Key assumptions)

A

Attraction between molecules is negligible
Volume of molecules small compared to volume of container
Molecules behave as elastic spheres (KE conserved)
Duration of the collision is much less than the time between collisions

242
Q

Brownian Motion

A

The erratic motion of small particles - provides evidence for the existence of molecules in gas or liquids.

243
Q

Three ways to increase gas pressure

A

Put more molecules in the container
Decrease volume of the container
Increase the average energy of the molecules

244
Q

Mean Square Speed

A

Directionally proportional to the temperature. If the temp doubles the mean square speed doubles and the root mean square speed increases by a factor of √2

245
Q

Two gases at the same temp

A

Their molecules have the same average KE.
At a fixed temp, if the molecules have a larger mass their average speeds will be lower. Inversely proportional to the mean square speed

246
Q

Internal Energy of an Ideal Gas

A

The sum of kinetic and potential energies of the particles in the gas.
However, potential energy is 0 in an ideal gas as there is no/negligible interactions between particles

247
Q

How does gas pressure change with volume? (Kinetic Theory)

A

If the volume is decreased, a greater number of molecules hit the inside of the container per second. Therefore a greater force will be exerted, which means a greater pressure.
This works in reverse for an increase in volume.

248
Q

How does gas pressure change with temperature? (Kinetic Theory)

A

If the temperature is increased, molecules will be moving at greater speeds so more molecules will be hitting the side of the container per second. This means a greater force will be observed and therefore a greater pressure.
This works in reverse for an decrease in temperature.

249
Q

Temperature

A

A measure of the average amount of energy that particles have
Particle energy: E ≈ kT

250
Q

Activation Energy

A

Minimum energy threshold for a reaction to take place

251
Q

Examples of processes where activation energy is key

A

Chemical reaction
Nuclear fusion
Semiconductors

252
Q

Why do all particles of a gas at a given temp not have a KE equal to the ave value?

A

Particles move at random, colliding frequently. On each collision, energy is exchanged at random between the two particles. Some will gain over several collisions (more energy than ave) and some will lose over several collisions (less energy than ave).

253
Q

The Boltzmann factor

A

The ratio of the number of particles in two different states
OR probability of a particle having activation energy ε in an environment of temperature T

254
Q

When does the particle energy = the activation energy

A

When the Boltzmann factor is e^-1 (0.37)

255
Q

Magnetic Field

A

A region of space which a force acts on:
- The poles of a magnet
- A current carrying conductor
- Moving charged particles

256
Q

Ways to increase the Field Strength of a circular iron core (3)

A

Increase the current
Increase the number of turns on a coil
Have a shorter circular core (smaller core)

257
Q

Right Hand Thumb Rule

A

Thumb in direction of wire (and current)
Fingers show direction of the field

258
Q

Solenoid

A

A coiled electrical conductor given a magnetic field by an electrical current

259
Q

Current flows from

A

Positive to Negative

260
Q

Magnetic Flux Density, B

A

A measure of magnetic field strength
Tesla, T OR Webers per m^2, Wbm^-2

261
Q

Magnetic Flux, Φ

A

The total flux intersecting at a given surface OR
“the product of the flux density and area of surface where the magnetic field lines intersect”
Weber, Wb

262
Q

Magnetic Flux Linkage

A

“The product of the flux and the number of turns in the coil”

263
Q

permittivity, μ

A

How well the core material transmits the magnetic field
The extent to which a medium concentrates lines of electrostatic flux (Fm^-1)

264
Q

What happens if a crack/air gap forms in a core

A

The permeance of the circuit decreases
There will be less flux for the given number of turns

265
Q

Fleming’s Left Hand Rule

A

Thumb - Direction of Force (F)
Pointer finger - Magnetic Field (B)
Middle finger - Current (I)

266
Q

Testing F = BIL

A

A current is passed through a conductive metal rod clamped tightly and held suspended in a magnetic field
The magnet is placed on an electric balance
The rod experiences a force due to the magnetic field
The magnet experiences an equal size force in the opposite direction. (If the force on the rod is upwards, the force on the magnet is downwards and vice versa)

267
Q

DC motors

A

Use a commutator to ensure that the current on one side remains in a constant direction.
The current through the coil switches direction every time the coil rotates through the vertical axis.
This means the direction of force remains constant and the turning force is maintained

268
Q

Electromagnetic Induction

A

Generating an electromotive force (EMF) by moving a conductor relative to a magnetic field

269
Q

Induction

A

The generation of EMF by forcing conductors to cut through lines of magnetic flux

270
Q

Flemming’s right hand rule

A

(When a conductor is moved in a field)
Thumb - Direction of Motion
Pointer Finger - Direction of magnetic field
Middle Finger - Direction of induced current

271
Q

Lenz’s Law

A

“The induced EMF is in a direction that opposes the change causing it”

272
Q

Faraday’s Law

A

“The EMF induced in a circuit is directly proportional to the rate of change of flux through the circuit”

273
Q

Transformers (Current turned on in input circuit)

A

Induces a B field in core.
Flux changes from zero to a value
Change in flux induces an EMF in the output coil

274
Q

Transformers (Current turned off in input circuit)

A

Flux changes from a value to zero
Change in flux induces and EMF the output coil (in opposite direction)

275
Q

Transformers (No change in current - constant)

A

No change in flux, so no EMF induced in output coil.

276
Q

What type of current do transformers work with? Why?

A

They only work with AC. This is because they need a constantly changing mag flux through the secondary current in order for them to work and for EMF to be induced.

277
Q

How to vary output p.d. for a given input (Transformers)?

A

Change the number of turns on the coil
Change the frequency at which the AC supply alternates

278
Q

Energy loss from a transformer

A

Energy may be lost through:
- Heat/Sound
- Power lost in coils (in order to minimise this use materials w/ low resistivity)

279
Q

Eddy Currents

A

Form in the core of a transformer. As the mag field forms, they form at right angles to the mag field.
They are loops of electrical current induced by a changing magnetic field (flow in closed loops w/in conductors)

280
Q

Reducing eddy currents

A

If a core is laminated parallel to the field then this limits the size of eddy currents and therefore the energy lost to them.

281
Q

What happens when a magnet falls through a copper tube?

A

As the magnet falls, the flux cutting the copper tube changes
This induces an EMF in the copper tube
As copper is a conductor, eddy currents form in the tube (which induce their own magnetic field)
As per Lenz’s Law, the current flows in a direction that will generate a mag field that opposes the falling of the magnet
This provides an upwards force on the falling magnet, which reduces its rate of fall (slows it down)

282
Q

How does a Speaker work?

A

AC occurs in coil - signal has same profile as the soundwave that will be produced
Changing current causes the coil to experience a force and oscillate w/ the same profile as the current
Causes the diaphragm to vibrate w/ the required frequency + amplitude to produce the sound

283
Q

How does a Microphone work?

A

Soundwaves hit the diaphragm and cause it to vibrate
This makes the coil oscillate up and down in the magnet
This induces an EMF w/ the same signal (frequency + amplitude) as the soundwaves

284
Q

Electric Field

A

A region of space within which charged particles feel a force

285
Q

What affects the size of the force experienced?

A

The electrical field strength
The particle charge

286
Q

Electrical field strength

A

The force acting per unit charge at that point
Units NC^-1 or Vm^-1

287
Q

Potential Difference

A

Work done per coulomb of charge

288
Q

Electric Potential

A

Work done in moving a unit positive charge from infinity to a point in an electric field

289
Q

Electrical fields on a charged particle

A

The direction in which the force acts on a +ve charge (-ve experience force in the opposite direction to the field lines)

290
Q

Uniform Electric Fields

A

A field in which the value of the field strength remains the same at all points

291
Q

Equipotential (electric fields)

A

Lines of equal electric potential (at a right angle to the field lines)

292
Q

What must be overcome to allow fusion?

A

The repulsive force between nuclei. In the suns core it must be Thermal Energy that overcomes the electrostatic potential energy and allow fusion to occur.

293
Q

Millikan’s Oil Drop

A

Atomiser used to spray tiny droplets of oil (which are negatively charged due to an x-ray source stripping them of electrons) into the space between two parallel plates.
The pd between the plates is adjusted until the majority of the droplets are suspended between them
The weight of the droplet is equal to the force pulling the droplet upwards
The charge on the droplet is then calculated. Only discrete values of charge were calculated, and the lowest common denominator was the charge on the electron.

294
Q

How does an electron gun work?

A

Through thermionic emission.
A metal filament is heated by passing a current through it. As it gets hotter the thermal velocity of the conduction electrons increases.
This then increases the chance of an electron escaping from the positive ions in the metal lattice

295
Q

Linear Accelerator (LINAC)

A

Electrons are fired from an electron gun and accelerated by an electric field. They are then focused into a narrow beam by a small hole in the anode.
The are then accelerated through drift tubes of alternating charges until they reach their target.
They are accelerated in a straight line.

296
Q

How does a Drift Tube work?

A

An electron accelerates towards a positively charged tube. When it enters the tube and passes through it, it is unaffected by the electric field and neither gains or loses velocity.
As it exits the tube, the charge switches and it accelerates away from the negative tube and towards the next +ve tube.
An AC current is used to alternate the charge on the tubes

297
Q

Why do adjacent drift tubes increase in length?

A

AC changes the charge in a fixed frequency (and therefore time period).
As the electron accelerates it takes less time to pass the same distance, so the tubes must be longer in order to be in sync with the changing current.

298
Q

Deflection of electrons

A

Fleming’s left hand rule
The higher the mass, the smaller the deflection for the same charge, field strength and distance

299
Q

How does a cyclotron work?

A

Two metal “Dees” are attached to an alternating pd (they sit between two poles of a magnet, one above and one below)
Charged particles are released between the Dees and accelerate across the gap due to the electric field
The mag field causes a spiral path of increasing radius (as velocity increases)
The voltage alternates in step with the frequency of rotation of particles, keeping everything synchronised

300
Q

Advantages of a cyclotron

A

Compact and efficient

301
Q

Disadvantages of a cyclotron

A

Strong uniform mag field is needed, difficult to control
At high energies, relativistic effects come into play
- mass does not remain constant, so the particle becomes out of synch with the dees

302
Q

Syncotrons

A

A cyclic particle acceleration that uses the concepts of both the LINAC and cyclotron to accelerate charged particles

303
Q

Acceleration chamber (sycotron)

A

Uses electric fields to accelerate the particles
The frequency of voltage oscillation must be changed to synchronise with with the arrival of particle bunches at decreasing time intervals

304
Q

Bending chamber (syncotron)

A

Uses mag fields to create a centripetal force
To maintain a circular path of constant radius, the mag field has to increase

305
Q

Particle tracks

A

Charged particles moving through a vapour/liquid leave a chain of ionised particles on which bubbles/condensates can nucleate
Detectors are placed in uniform magnetic fields, allowing us to infer a number of things from the particle track

306
Q

Tells in a particle trail

A

Direction - charge on particle (flemmings LH rule)
Radius - momentum on particle
Thickness - relates to speed (slower = thicker)
Thickness - Relates to ionising power
Length - relates to life of particle

307
Q

Atomic Number (Z)

A

The number of protons in the nucleus

308
Q

Nucleon/Mass Number (A)

A

The total number of nucleons in the nucleus

309
Q

Neutron Number

A

The number of neutrons in the nucleus

310
Q

Isotope

A

Same atomic number, different mass number
(same protons, more/less neutrons)

311
Q

JJ Thompson

A

Discovered electrons using cathode ray tubes - proved atoms are not most fundamental particle

312
Q

James Chadwick

A

Discovered the Neutron

313
Q

Rutherford, Geiger and Muller

A

Discovered vast majority of mass and all +ve charge is concentrated in nucleus of atom

314
Q

Rutherford’s Alpha Particle Scattering Experiment

A

Prev atomic models said small spheres of -ve charge suspended in +ve charge (Plum Pudding)
Alpha particles where fired at a thin sheet of gold foil with a phosphor around.
Some deflected as expected (small/no change)
Around 1/8000 deflected over 90°, which defied plum pudding model

315
Q

Rutherford Scattering

A

Also known as Coulomb Scattering and Elastic Scattering
Relies on static electric (coulomb) forces
The distance of closes approach is set by this and the speed of incoming particles
Energy + velocity of outgoing scattered particles is the same as the energy + velocity they started with
The deflection of charged particles on a collision course/passing close to a nucleus

316
Q

Fundamental Particles

A

Particles that cannot be broken down any further

317
Q

Approx Diameter of an Atom

A

1*10^-10 m

318
Q

Approx Diameter of an Electron

A

1*10^-18 m

319
Q

Approx Diameter of a Nucleus

A

1*10^-14 m

320
Q

Approx Diameter of a Nucleon

A

1*10^-15 m

321
Q

Approx Diameter of a Quark

A

1*10^-18 m

322
Q

Anti-Particle

A

A particle with the same mass but opposite charge and opposite quantum spin.
An antimatter version of a particle

323
Q

Up Quark

A

Has a relative charge of +2/3

324
Q

Down and Strange Quark

A

Have a relative charge of -1/3

325
Q

Three main categories of Fundamental Particles

A

Quarks - include the up and down quarks (are what protons + neutrons are composed of)
Leptons - include electrons and neutrinos
Force Carriers

326
Q

Photon, γ (Particle Physics)

A

A force carrier for the electromagnetic force.
Responsible for interactions between charged particles
Range: No Limit
Relative strength: 10^0

327
Q

Gluon, g (particle physics)

A

A force carrier for the strong nuclear force
Holds together protons + neutrons in nuclei of atoms
(Holds together quarks to form hadrons)
Range: 10^-15 m
Relative Strength: 10^3

328
Q

Z boson and W boson

A

Both are force carriers.
Responsible for radioactive decay of subatomic particles, inc beta decay
Range: 10^-18 m
Relative Strength: 10^-10

329
Q

Gravity (particle physics)

A

Responsible for the attraction between objects with mass.
Range: No limit
Relative strength: 10^-34
Has a suspected force carrier called the graviton, but it has not been found as of yet

330
Q

Hadrons

A

A combination of bonded quarks

331
Q

Baryon

A

Made from thee quarks or three antiquarks

332
Q

Meson

A

Made from a quark - antiquark pair

333
Q

Properties of a Hadron

A

Charge - Determined by the quarks used
Baryon Number - 1 if a baryon OR 0 if a meson
Strangeness:
“-1” if one strange quark
“-2” if two strange quark (ect)
“1” if one strange antiquark
“2” if two strange antiquark (ect)

334
Q

Properties that must be conserved under particle interaction

A

Lepton number
Charge
Baryon Number
Momentum
Mass + Energy (E = mc^2)

335
Q

Pair Production

A

The creation of a particle-antiparticle pair from a high energy photon

336
Q

Pair Annihlation

A

When a particle-antiparticle pair collide and annihilate, their combined masses convert to two photons

337
Q

Rest Energy

A

The energy a particle at rest would produce if converted into energy (E = mc^2)
m = Rest Mass

338
Q

Particle Energy

A

The energy associated with a particle in motion.

339
Q

Atomic Mass Unit, u

A

Defined as 1/12 of the mass of a carbon-12 atom
1.66 * 10^-27 kg

340
Q

MeV/c^2 to kg

A
  • 1.610-19 (convert to J/c^2)
    /(3    10^8)^2 (divide by c^2)
341
Q

Standing wave model

A

Electrons surrounding a nucleus can be modelled as standing waves trapped in a ‘well’ of potential w/ a fixed width
This model doesn’t quite predict the energy level we actually observe.
It has only ever worked for a hydrogen nucleus

342
Q

Why do we fire electrons at matter?

A

To obtain an image of the matter.
Often used to observe structures smaller than the wavelength of visible light.
The greater the momentum the smaller the wavelength and the smaller the resolution

343
Q

What wavelength allows us nuclei to diffract electrons?

A

A de Broglie wavelength of approx 10^-15 m
An interference pattern forms as electron waves pass either side of the nucleus

344
Q

How was the structure of the proton determined?

A

Deep Inelastic Scattering of High-Energy Electrons.
At low energies, photons behave as a blur of charge
When high energy electrons are fired at protons, relativistic effects cause it to appear as though the electrons interact with a flat surface with stationary centres of charge
Therefore the electrons deflect as they pass through the proton. A jet of particles are also created in the interaction.

345
Q

Deep (proton structure)

A

The electrons are able to penetrate deep inside the hadron

346
Q

Inelastic (proton structure)

A

Not all energy is converted in the collision - some energy into mass/new particles

347
Q

Scattering (proton structure)

A

Scattering + diffraction pattern suggests 3 points of deflection - three sub particles in proton

348
Q

High-energy (proton structure)

A

Have to have high momentum in order to have a short enough wavelength

349
Q

Decay Constant, λ

A

The probability a particular nucleus would decay in a unit time

350
Q

Activity

A

Number of decay’s per second
Proportional to number of parent isotopes
Becquerel, Bq

351
Q

Alpha decay, α

A

2 protons, 2 neutrons
Charge of +2e, mass of 4u
Deflected in magnetic field
Travels slowly (<5% speed of light) - quickly loses energy
Only travels a few cm through air
Absorbed by a sheet of paper
Heavily ionising

352
Q

Alpha decay equation

A

parent isotope -> daughter isotope + alpha particle (α)

353
Q

Beta decay, β

A

Formed of an electron (or in rare cases a positron)
Charge of -1e, mass of 9.11 *10^-31 kg
Deflected in a magnetic field
Energy ranges between 0.2 and 3.0 MeV (travels up to 99% speed of light)
Less likely to interact w/ air molecules, less ionising, travels further
Does not travel in a straight line (as low mass, deflects easily)
Absorbed by approx 3mm Aluminium

354
Q

β- decay

A

Neutrons in the nucleus undergo β- decay, releasing and e- and turning into a proton
parent isotope -> daughter isotope + β- + anti-neutrino

355
Q

β+ decay

A

Protons in the nucleus undergo β+ decay, releasing a positron and turning into a neutron
parent isotope -> daughter isotope + β+ + neutrino

356
Q

Gamma decay, γ

A

Uncharged, high-frequency EM radiation
Can be diffracted, reflected, refracted and produces interference patterns
Travels at the speed of light
Decreases in intensity w/ distance from a point, inverse square law
Interacts very little w/ air molecules
Unaffected by magnetic fields
Can penetrate several cm of lead

357
Q

Why does gamma occur?

A

Occurs when a nucleus is in an excited state and falls to a more stable state, releasing a photon
No particles are lost from the nucleus of an atom
Excited nuclei marked with a *

358
Q

Half Value Thickness, HVT

A

The thickness of a particular material that is required to halve the intensity of radiation

359
Q

N-Z Plots

A

Plotting the number of neutrons against the number of protons for all known isotopes allows us to estimate the type of radioactive decay an isotope may undergo (or N against Z)

360
Q

Proton to Neutron Ration

A

Small nuclei tend to have a 1:1 ratio of neutrons to protons
Larger nuclei tend to have a 1.5:1 ratio of neutrons to protons

361
Q

Radiation on a Body

A

When radiation is incident on a body, some is reflected (scattered), some is absorbed and some transmitted
Radiation deposits its energy in matter through ionisation and this takes place in the cells of tissues, giving rise to damage to important molecules

362
Q

Absorbed Dose, D

A

Mean energy absorbed per unit mass when exposed to radiation

363
Q

Equivalent Dose, H

A

Similar to Gray (absorbed dose), but multiplied by a Quality factor. The quality factor depends on the biological damage done by a particular type of radiation.

364
Q

Q value for electrons, muons and photons

A

Q = 1

365
Q

Q value for high energy protons and neutrons

A

Q = 10

366
Q

Q value for Alpha particles (and other atomic nuclei)

A

Q = 20

367
Q

Radiation Sources (Natural vs Man-Made)

A

80% Natural Sources
20% Man-Made Sources

368
Q

Natural sources (% of the 80%)

A

53% Air (mainly Radon gas)
16% Cosmic radiation (depends on altitude)
20% Terrestrial sources (rocks and soil)
12% Food and Drink

369
Q

Man-Made sources (% of the 20%)

A

96% Medical uses
3.9% Consumer goods
0.09% Nuclear Testing/Accidents
0.001% Nuclear Power

370
Q

The max legal radiation dosage per year?

A

20 mSv/yr
This is the maximum unavoidable dose (eg background radiation or hazards of a particular job)

371
Q

Where does all of our energy ultimately come from?

A

Atomic Nuclei
Energy from sun - Fusion
Nuclear reactors - Fission
Geothermal energy - (mostly) Radioactive Decay

372
Q

Energy from radioactive decay

A

During decay, the total mass of the products is slightly less than the total mass of the initial nuclei

373
Q

Binding Energy

A

Forces hold the nuclei together, so work must be done to separate a nucleus into individual nucleons
The energy needed to split a nucleus into its nucleons is known as the binding energy

374
Q

Significance of a high binding energy per nucleon

A

Isotopes with the highest binding energy require more energy to break apart, therefore are more stable
An elements binding energy can be found by the mass deficit of the atom relative to individual nucleons

375
Q

When is energy released (radioactive decay)

A

When light nuclei combine (fusion) or when heavy nuclei split (fission)
This increases the binding energy, creating more stable nuclei, and releasing energy to the surroundings

376
Q

Fission

A

Large unstable nuclei (like Plutonium or Uranium) will decay spontaneously (decay can also be triggered by the nuclei being hit by a neutron)
The nuclei splits into two (unevenly sized) nuclei (some neutrons are also released, along with some energy
Energy can be released as radiation, but is primarily released as KE (heat) which allows things like the heating of water to drive turbines
The extra neutrons produced may collide with further heavy nuclei if present, resulting in a chain reaction

377
Q

What is binding energy often given as?

A

A negative number
It can be thought of as the energy required to break the break the nucleus apart - to overcome the strong nuclear force. When it is plotted as such, it can be thought of as an “energy valley” with a minimum near iron, nuclei more and less massive than iron will move towards it via fission/fusion

378
Q

Other names for Fusion

A

Nuclear Burning
Hydrogen Burning
Nucleosynthesis

379
Q

The stages of fusion (proton-proton chain reaction)

A

1) Two protons fuse to form a deuterium nucleus - they need a lot of KE to overcome electrostatic repulsion (2 protons -> 1 proton + 1 neutron + some change)
2) A proton and a deuterium combine together to form a Helium-3 nucleus
3) Two Helium-3 nuclei combine to form a Helium-4 nucleus and two protons
Once all the hydrogen in the core of a star is used, helium burning may begin

Physics (OCR B) (2 decks)

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