Current (I) — rate of flow of charge. Unit: ampere (A). Measured with an ammeter (in series).
Potential difference / voltage (V) — energy transferred per unit charge. Unit: volt (V). Measured with a voltmeter (in parallel).
Resistance (R) — how difficult it is for current to flow. Unit: ohm (Ω).
Ohm's Law: V = IR. Also: I = V/R and R = V/I.
Charge: Q = It (charge = current × time). Unit: coulombs (C).
Series and parallel circuits
Series: same current everywhere, voltages add up, total resistance = sum of all resistors.
Parallel: voltage same across each branch, currents add up, total resistance is less than the smallest individual resistor.
Adding resistors in series → total resistance increases → current decreases.
Adding resistors in parallel → total resistance decreases → current from battery increases.
Component IV characteristics
Ohmic resistor — straight line through origin. Constant resistance.
Filament lamp — S-curve (resistance increases as it gets hotter). Curve bends away from current axis.
Diode — only conducts in one direction. Very high resistance in reverse. Steep rise in forward direction.
Thermistor — resistance decreases as temperature increases (NTC). Used in thermostats.
LDR (light-dependent resistor) — resistance decreases as light intensity increases. Used in automatic lights.
Power equations
P = IV (power = current × voltage).
P = I²R.
P = V²/R.
Energy = Power × time (E = Pt).
Units: power in watts (W), energy in joules (J), time in seconds (s).
Exam questions — 3 questions · 10 marks
⚡ Extended questions included. Show all working for calculation questions. The AI marks against the real AQA mark scheme.
1 markOhm's LawAQA 8463 P1 style
A resistor has a potential difference of 12 V across it and a current of 3 A through it. What is its resistance?
A 36 Ω
B 4 Ω
C 0.25 Ω
D 9 Ω
1 markIV characteristicAQA 8463 P1 style
The IV graph for a component shows a curve that increases steeply in one direction and stays close to zero in the other direction. What is the component?
A Ohmic resistor
B Filament lamp
C Diode
D Thermistor
4 marksSeries vs parallel analysisAQA 8463 P1 style
Two identical 6 Ω resistors are connected (a) in series and (b) in parallel to a 12 V battery. For each, calculate the total resistance and the total current from the battery. (4 marks)
Hint: Series: R_total = R1 + R2. Parallel: 1/R_total = 1/R1 + 1/R2 (or use product/sum for two resistors). Then I = V/R.
+40 XP
3 marksPower calculationAQA 8463 P1 style
A kettle operates at 230 V and draws a current of 9 A. Calculate (a) the power of the kettle and (b) the energy transferred in 3 minutes. (3 marks)
Hint: P = IV. Then E = Pt (convert minutes to seconds first).