# Unit 1 - Electricity

### Description

Mindmap of AS Physics Unit 1, Section 3 - Electricity (AQA), from the AQA exam board. If you need any help or have any suggestions, contact me directly on ExamTime or email me on: cmcclintock977@gmail.com
Mind Map by Callum McClintock, updated more than 1 year ago
 Created by Callum McClintock about 9 years ago
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## Resource summary

Unit 1 - Electricity
1. Circuit Diagrams
1. Series & Parallel
1. Symbols
2. Current & Potential Difference
1. Current is the rate of flow of charge
1. I = Q / t
2. Pd is the work done in moving a unit charge between two points
1. V = W / Q
3. Resistance
1. The hindrance to the flow of charge
1. R = V / I
1. Ohmic Conductors
1. Obey Ohm's law
1. I is directly proportional to V
1. If temperature is constant
2. I-V Characteristics
1. I-V Graphs
1. The lower the gradient, the higher the resistance
1. Metallic Conductors
1. Filament Lamps
2. Semiconductors
1. Quite good conductors
1. But not as good as metals due to fewer charge carriers
1. However, if energy is supplied to a semiconductor (e.g. a rise in temperature), more charge carriers can be released and the resistance decreaes
2. Components
1. Thermistors
1. Diodes
1. LDRs
2. Resistivity & Superconductors
1. Resistivity is the resistance of a 1m length with a 1m^2 cross-sectional area
1. ρ = RA / L
2. You can lower the resistivity of some metals by cooling them down
1. Reach a transition temperature and resistivity disappears entirely - superconductors
1. Without any resistance, no electrical energy is wasted as heat, so none is lost
1. This transition temperature is below 10 kelvin (-263°C) for most 'normal' conductors
1. It is tricky and very expensive to reach such temperatures
2. Superconductors can be used for cables with no loss of power, really strong electromagnets, and high-speed circuits
2. Power & Electrical Energy
1. Power Equations
1. P = E / t
1. P = VI
1. P = V^2 / R
1. P = I^2R
2. Energy Equations
1. E = VIt
1. E = (V^2 / R)t
1. E = I^2Rt
2. E.m.f & Internal Resistance
1. E.m.f is the amount of electrical energy a battery produces and transfers to each coulomb of charge
1. You can use a V-I graph to calculate ℰ and r
1. The y-intercept (c) is ℰ and the gradient (m) is -r
2. Equations
1. ℰ = E / Q
1. ℰ = I(R + r)
1. ℰ = V + v
1. V = ℰ - v
1. V = ℰ - Ir
2. Conservation of Energy & Charge
1. Kirchhoff's Laws
1. First Law
1. The total current entering a junction = the total current leaving it
2. Second Law
1. The total e.m.f. around a series circuit = the sum of the p.d.s across each component
1. ℰ = ΣIR
3. In circuits
1. Parallel
1. 1 / R total = (1 / R1) + (1 / R2) + (1 / R3)...
1. Series
1. R total = R1 + R2 + R3...
1. ℰ total = ℰ1 + ℰ2 + ℰ3...
2. The Potential Divider
1. At its simplest, a potential divider is a circuit with a voltage source and a couple of resistors in series
1. You can use potential dividers to supply a p.d., V out, between zero and the p.d. across the power supply.
1. V out = (R2 / R1 + R2)Vs
1. Uses
1. Light sensors
1. Temperature sensors
1. Potentiometers
2. Alternating Current
1. An AC or AV is one that changes with time
1. Oscilloscopes
1. An AC source gives a regular repeating waveform
1. 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
1. Equations
1. f = 1 / T
1. V rms = V0 / sqrt2
1. P = V rms * I rms
1. R = V rms / I rms
1. R = V0 / I0

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