A-Level Physics: Circuits, EMF and Internal Resistance

Electricity at A-Level is a systems topic: every question is a small circuit to be analysed, and the marks go to students who track current, potential difference and resistance through it methodically. This quiz builds that method across the full first-year electrical content.

The component-level questions cover resistivity applied to a real copper wire (converting the cross-sectional area from mm² correctly — the classic slip), the I-V characteristics of ohmic conductors, filament lamps and diodes, which components are genuinely non-ohmic, and what actually affects resistivity (material and temperature, never geometry — a distinction the multiple-choice format tests cleanly). A diode circuit with a 0.7 V forward drop brings the semiconductor behaviour into a calculation.

The circuit-analysis questions combine resistors in series and parallel — including the two-in-parallel-plus-one-in-series arrangement — and then move to the topic's centre of gravity: EMF and internal resistance. One multi-statement question (its key verified during checking against the solver's own self-contradictory reasoning) works a 12 V battery with internal resistance through current, lost volts, terminal pd and load power; another recovers the load resistance from the drop in terminal pd.

The potential-divider questions close the set with the sensor applications examiners favour: the output change when an LDR's resistance falls under brighter light, and the voltage across a thermistor at a given temperature — both worked through the divider ratio explicitly.

All values are supplied, data-booklet style, and every explanation traces the full chain — total resistance, current, then each pd — the same order marks are awarded in.

• Apply resistivity with correct unit conversions of area
• Recognise the I-V characteristics of ohmic and non-ohmic components
• Combine series and parallel resistors in mixed arrangements
• Analyse EMF, internal resistance, lost volts and terminal pd systematically
• Solve potential divider circuits with LDRs and thermistors

Topic scope follows section 3.5.1 (Current electricity) of the current a-level physics subject content: charge and current, resistivity, I-V characteristics, circuit combinations, EMF and internal resistance, and the potential divider.