GCSE Physics, Unit 2, Lesson 1 of 6

Circuit symbols, charge and current

GCSE Physics, Electric circuits, 20 minutes

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The symbols you draw circuits with, what a current is, and Q = It with the unit traps that catch people out.

What you will learn

  • Name and draw the standard circuit symbols
  • Place an ammeter and a voltmeter correctly
  • Calculate charge, current or time with Q = It, converting mA and minutes

Drawing a circuit

Circuit diagrams use standard symbols so anyone can read them.

Learn these fourteen:

cellbatteryopen switchclosed switchfixed resistorvariable resistorlampfusediodeLEDLDRthermistorAammeterVvoltmeter
  • A battery is two or more cells joined together. The long plate is the positive side.
  • Arrows pointing out mean light leaves (LED). Arrows pointing in mean light arrives (LDR).
  • An ammeter measures current. It goes in series, in the same loop as the component.
  • A voltmeter measures potential difference. It goes in parallel, across the component's two ends.
  • A diode lets current flow in one direction only. An LED (light-emitting diode) is a diode that gives out light.
  • An LDR (light-dependent resistor) is a resistor whose resistance changes with light. A thermistor is a resistor whose resistance changes with temperature.
  • A fuse is a thin wire that melts and breaks the circuit if the current gets too big.
  • A variable resistor has a resistance you can change by hand. A dimmer switch for a lamp is one.

Telling similar symbols apart:

  • Cell: one long and one short plate. Battery: two or more cells joined.
  • Fixed resistor: a plain rectangle. Fuse: a rectangle with the wire running through it. Variable resistor: a diagonal arrow through the rectangle. Thermistor: a bent line through the rectangle, with the flat end at the bottom.
  • Lamp: a circle with a cross in it.
  • Open switch: the lever lifted from the gap. Closed switch: the lever lying flat across the gap.
  • Diode: a triangle pointing at a bar. LED: a diode with two arrows pointing out. LDR: a rectangle in a circle with two arrows pointing in.

Draw wires as straight lines with a ruler, and leave no gaps: a gap means the circuit is broken.

The rest of this lesson and its 7 practice questions are locked.

In this lesson

  1. Drawing a circuit
  2. Charge and current
  3. Watch the units
  4. Try it: Your first charge calculation

7 practice questions, marked as you go; about 20 minutes in all.

Key terms

Battery, Out, Ammeter, Voltmeter, Diode, LDR, Thermistor, Fuse, Variable resistor, Closed circuit

In this unit: Electric circuits

Circuit symbols, charge and current, V = IR, I-V graphs, series and parallel circuits, and sensing circuits with LDRs and thermistors.

All of Electric circuits

Back to the unit