Electricity flashcards

Electricity is a core topic in GCSE Physics covering how charge flows in circuits, the behaviour of current, voltage and resistance, and how these quantities relate through Ohm's law. Students must understand series and parallel circuits, how to calculate power and energy, and the characteristics of components such as resistors, filament bulbs, diodes and LDRs. The topic also includes the domestic mains supply, the role of the live, neutral and earth wires, fuses and circuit breakers, and how to stay safe with electricity. Understanding the difference between direct current and alternating current is also required, along with calculations involving charge, energy and the national grid.

1. Card 1

   What is electric current and what unit is it measured in?

   Electric current is the rate of flow of electric charge. It is measured in amperes (amps, A).

2. Card 2

   State the equation linking charge, current and time.

   Charge (Q) = current (I) x time (t). Charge is measured in coulombs (C), current in amps and time in seconds.

3. Card 3

   What does potential difference (voltage) mean in a circuit?

   Potential difference is the energy transferred per unit charge between two points. It is measured in volts (V).

4. Card 4

   State Ohm's law and the equation that goes with it.

   Ohm's law states that current is directly proportional to potential difference at constant temperature. The equation is V = I x R, where R is resistance in ohms.

5. Card 5

   How does resistance affect current in a circuit?

   The greater the resistance, the smaller the current for a given voltage. Resistance opposes the flow of charge and is measured in ohms (Ω).

6. Card 6

   How do you find the total resistance in a series circuit?

   In a series circuit, total resistance = R1 + R2 + R3. All resistances simply add together, so total resistance is always greater than any individual resistor.

7. Card 7

   What happens to voltage and current in a parallel circuit?

   In a parallel circuit, voltage across each branch is the same. Current splits between branches, so total current equals the sum of branch currents.

8. Card 8

   What is the difference between an ohmic and a non-ohmic conductor?

   An ohmic conductor has constant resistance; current is proportional to voltage. A non-ohmic component, like a filament bulb, has resistance that changes with temperature.

9. Card 9

   What is the I-V characteristic of a diode?

   A diode only allows current to flow in one direction. It has very high resistance in the reverse direction, so current is effectively zero when connected the wrong way.

10. Card 10

    State the two equations for electrical power.

    Power (P) = voltage (V) x current (I), and also P = I squared x R. Power is measured in watts (W).

11. Card 11

    What is the difference between direct current (d.c.) and alternating current (a.c.)?

    Direct current (d.c.) flows in one direction only. Alternating current (a.c.) repeatedly reverses direction; UK mains supply is a.c. at 230 V and 50 Hz.

12. Card 12

    What are the roles of the live, neutral and earth wires in a mains plug?

    The live wire carries the high voltage. The neutral wire completes the circuit. The earth wire is a safety wire that protects against electric shock if the appliance develops a fault.

• Many students confuse current and voltage, thinking current is used up as it travels around a circuit, when in fact current is the same throughout a series circuit.
• Students often forget that resistance in a parallel circuit is always less than the smallest individual resistor, and incorrectly add resistances as they would in a series circuit.
• A common error is mixing up the live and neutral wires when explaining safety; it is the live wire that is dangerous because it carries the high voltage, not the neutral wire.

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