Edexcel GCSE Physics Topic 10: Electricity and Circuits Exam Questions

About Edexcel GCSE Physics Topic 10: Electricity and Circuits

Topic 10 is a core part of Paper 2. It covers current as the rate of flow of charge, potential difference as energy transferred per unit charge, resistance and Ohm's law, and how current and potential difference behave in series and parallel circuits. You need to sketch and explain I-V graphs for a fixed resistor, filament lamp and diode, and describe how LDRs and thermistors are used as sensors. The topic finishes with energy and power in circuits, the heating effect of current, and mains electricity and plug safety. It links to Topics 11 to 13. The core practical on investigating resistance and I-V characteristics is regularly examined.

What you need to know

• Charge and current Charge Q = I x t, measured in coulombs. Current is the rate of flow of charge, measured in amps with an ammeter in series.
• Potential difference Energy transferred E = Q x V. Potential difference is measured in volts with a voltmeter in parallel.
• Resistance V = I x R. In series, total resistance is the sum of the resistances and current is the same everywhere. In parallel, p.d. is the same across each branch and adding branches reduces total resistance.
• I-V characteristics A fixed resistor gives a straight line through the origin. A filament lamp curves because resistance increases as it heats up. A diode only lets current flow in one direction.
• Sensors LDR resistance decreases as light intensity increases. Thermistor resistance decreases as temperature increases. They are used in potential dividers for automatic lighting and thermostats.
• Power and energy P = I x V, P = I^2 x R and E = I x V x t. Current causes heating because electrons collide with ions in the lattice.
• Mains electricity UK mains is a.c. at 230 V and 50 Hz. The live wire carries the voltage, the neutral completes the circuit and the earth wire is a safety wire. Fuses and circuit breakers break the circuit if the current is too large.

Common mistakes in Topic 10: Electricity and Circuits

• Saying current is used up in a circuit. Current is the same before and after a component in series; it is energy that is transferred.
• Connecting a voltmeter in series. Voltmeters go in parallel across a component.
• Saying adding resistors in parallel increases total resistance. It decreases total resistance because there are more paths for current.
• Describing LDR or thermistor behaviour the wrong way round. Resistance falls as light intensity or temperature rises.
• Saying the earth wire carries current in normal use. It only carries current if a fault makes the casing live.

Try three Topic 10: Electricity and Circuits exam-style questions