Mindmap of AS Physics Unit 1, Section 3 - Electricity (AQA), from the AQA exam board.
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2.2 Pd is the work done in moving a unit
charge between two points
2.2.1 V = W / Q
3 Resistance
3.1 The hindrance to the flow of charge
3.2 R = V / I
3.3 Ohmic Conductors
3.3.1 Obey Ohm's law
3.3.2 I is directly proportional to V
3.3.2.1 If temperature is constant
4 I-V Characteristics
4.1 I-V Graphs
4.1.1 The lower the gradient, the
higher the resistance
4.1.2 Metallic Conductors
4.1.3 Filament Lamps
4.2 Semiconductors
4.2.1 Quite good conductors
4.2.1.1 But not as good as
metals due to fewer
charge carriers
4.2.1.2 However, if energy is supplied to a semiconductor
(e.g. a rise in temperature), more charge carriers
can be released and the resistance decreaes
4.2.2 Components
4.2.2.1 Thermistors
4.2.2.2 Diodes
4.2.2.3 LDRs
5 Resistivity & Superconductors
5.1 Resistivity is the resistance of a 1m
length with a 1m^2 cross-sectional area
5.1.1 ρ = RA / L
5.2 You can lower the resistivity of
some metals by cooling them down
5.2.1 Reach a transition temperature and
resistivity disappears entirely - superconductors
5.2.1.1 Without any resistance, no electrical
energy is wasted as heat, so none is lost
5.2.1.2 This transition temperature is below 10
kelvin (-263°C) for most 'normal' conductors
5.2.1.2.1 It is tricky and very expensive to
reach such temperatures
5.2.1.3 Superconductors can be used for cables with no loss of
power, really strong electromagnets, and high-speed circuits
6 Power & Electrical Energy
6.1 Power Equations
6.1.1 P = E / t
6.1.2 P = VI
6.1.3 P = V^2 / R
6.1.4 P = I^2R
6.2 Energy Equations
6.2.1 E = VIt
6.2.2 E = (V^2 / R)t
6.2.3 E = I^2Rt
7 E.m.f & Internal Resistance
7.1 E.m.f is the amount of electrical energy a battery
produces and transfers to each coulomb of charge
7.1.1 You can use a V-I graph to calculate ℰ and r
7.1.1.1 The y-intercept (c) is ℰ and the gradient (m) is -r
7.2 Equations
7.2.1 ℰ = E / Q
7.2.2 ℰ = I(R + r)
7.2.2.1 ℰ = V + v
7.2.2.1.1 V = ℰ - v
7.2.2.1.1.1 V = ℰ - Ir
8 Conservation of Energy & Charge
8.1 Kirchhoff's Laws
8.1.1 First Law
8.1.1.1 The total current entering a
junction = the total current
leaving it
8.1.2 Second Law
8.1.2.1 The total e.m.f. around a series
circuit = the sum of the p.d.s across
each component
8.1.2.1.1 ℰ = ΣIR
8.2 In circuits
8.2.1 Parallel
8.2.1.1 1 / R total = (1 / R1) + (1 / R2) + (1 / R3)...
8.2.1.2
8.2.2 Series
8.2.2.1 R total = R1 + R2 + R3...
8.2.2.2 ℰ total = ℰ1 + ℰ2 + ℰ3...
9 The Potential Divider
9.1 At its simplest, a potential
divider is a circuit with a
voltage source and a couple
of resistors in series
9.1.1 You can use potential
dividers to supply a p.d., V
out, between zero and the
p.d. across the power supply.
9.1.1.1 V out = (R2 / R1 + R2)Vs
9.1.1.2 Uses
9.1.1.2.1 Light sensors
9.1.1.2.2 Temperature sensors
9.1.1.2.3 Potentiometers
10 Alternating Current
10.1 An AC or AV is one that
changes with time
10.1.1 Oscilloscopes
10.1.1.1 An AC source gives
a regular repeating
waveform
10.1.1.2 A DC source is always at
the same voltage, so you
get a horizontal line.
You'd get a dot on the
voltage axis if the time
base was turned off