GCSE Physics: Electricity — Topic Revision Workbook

Inside GCSE Physics: Electricity — Topic Revision Workbook

read circuit symbols and tell series from parallel circuits, use Q = It for charge and V = IR (Ohm's law) for potential difference, add resistances in series and read the I–V graphs of an ohmic conductor, a filament lamp and a diode plus the LDR and thermistor, then calculate power with P = VI and P = I²R and revise mains electricity, the plug wires and the National Grid. About 30 minutes.

Learning objectives

• circuits — standard circuit symbols, the ammeter (in series) and voltmeter (in parallel), and how current and potential difference behave in series and parallel circuits;
• charge and Ohm’s law — charge with Q = I × t, and potential difference with V = I × R, rearranged to find resistance or current;
• resistance and I–V characteristics — resistors in series (add) and parallel (idea), the graphs of an ohmic conductor, a filament lamp and a diode, and the LDR and thermistor;
• power and energy — P = V × I, P = I² × R and E = P × t (and E = Q × V);
• mains electricity — a.c. at about 230 V and 50 Hz, the live, neutral and earth wires and the fuse, and the National Grid with step-up and step-down transformers.

Activities in this book

1. Task 1 — Circuit Symbols & Series and Parallel

   learn the standard circuit symbols. An ammeter (a circle with the letter A) measures current and goes in series; a voltmeter (a circle with the letter V) measures potential difference and goes in parallel across a component. In a series circuit the current is the same everywhere; in a parallel circuit the current splits between the branches.

2. Task 2 — Charge & Ohm’s Law

   charge, current and time are linked by Q = I × t (charge in coulombs, current in amps, time in seconds). Potential difference, current and resistance are linked by Ohm's law V = I × R. Rearrange it to find resistance (R = V ÷ I) or current (I = V ÷ R). Always write the numbers in before you divide or multiply.

3. Task 3 — Resistance & I–V Characteristics

   resistors in series simply add up (R_total = R₁ + R₂), while adding resistors in parallel gives a total resistance that is less than the smallest. An ohmic conductor at constant temperature gives a straight-line I–V graph; a filament lamp curves because its resistance rises as it heats; a diode only conducts one way. An LDR’s resistance falls in brighter light, and a thermistor’s resistance falls as it gets hotter.

4. Task 4 — Power, Energy & Mains Electricity

   electrical power is P = V × I, and also P = I² × R. Energy transferred is E = P × t (or E = Q × V). UK mains is alternating current (a.c.) at about 230 V and 50 Hz. In a three-pin plug the live wire is brown, the neutral is blue and the earth is green-and-yellow; a fuse breaks the circuit if the current gets too high. The National Grid uses transformers to change the voltage.

5. Task 5 — Mains Safety Extended Answer

   a 6-marker rewards clear, ordered physics. Plan first: name each wire and its job, then explain how the earth wire and fuse work together. Use exam keywords — live, neutral, earth, fuse, current, melts, breaks the circuit, casing, safe.

Suggestions for teaching

• Fix the symbols and meters first. Make sure learners place the ammeter in series and the voltmeter in parallel before analysing whole circuits.
• Drill the three equations. Q = It, V = IR and P = VI (and P = I²R). Insist on writing the numbers in with units before calculating.
• Rearrange with care. Practise V = IR → R = V ÷ I and I = V ÷ R until swapping the subject is automatic.
• Read graphs, not just recall them. Contrast the straight line of an ohmic conductor with the curves of a filament lamp and a diode, and link the LDR and thermistor to sensing circuits.
• Make mains real and safe. Name the wire colours, and explain the earth-and-fuse partnership — the exact skill Task 5 rehearses.