Electrical components and circuit symbols: the chart of cell, battery, open and closed switch, lamp, fixed and variable resistor, diode, LED, fuse, ammeter, voltmeter, thermistor, LDR, motor and buzzer, what each one does in a circuit, how to draw a circuit diagram that gets the marks, the series and parallel rules for current and potential difference, V = I R, and a printable symbol sheet

A circuit diagram is a drawing of a circuit using a fixed set of symbols, so that any reader can build or analyse the circuit without a photograph. The set is standard (BS EN 60617 in the UK, and the same shapes in American and Australian courses), the GCSE specifications list the ones students must draw and recognise, and the marks on a circuit question go for three things: the right symbol, the right connection (an ammeter in series, a voltmeter in parallel) and a diagram drawn with a ruler. The chart, the rules and the drawing method are below, with the printable symbol sheet.

Download the circuit symbols sheet (PDF) (the symbols drawn and named with what each does on page 1, the series and parallel rules, the equations and a practice set with answers on page 2; two pages, free).

The components and their symbols

Two conventions that carry marks. On a cell, the long line is positive; conventional current flows out of it round the circuit to the short line. On a diode, the arrow shows the direction current can flow.

Connecting meters

• Ammeter: in series. It measures the current through a component, so the current must pass through the meter. An ideal ammeter has almost no resistance, so it does not change the circuit.
• Voltmeter: in parallel. It measures the potential difference across a component, so it connects to the two ends of that component on its own branch. An ideal voltmeter has very high resistance, so almost no current takes the detour.

The two mistakes that cost the most marks: a voltmeter drawn in the main loop (it would stop the current) and an ammeter drawn across a component (it would short it out).

Series and parallel: the rules

The AQA GCSE specification states the rules exactly, and they are the same in every course.

Series circuit (one loop): - "there is the same current through each component" - "the total potential difference of the power supply is shared between the components" - the resistances add: R total = R1 + R2

Parallel circuit (branches): - "the potential difference across each component is the same" - "the total current through the whole circuit is the sum of the currents through the separate components" - "the total resistance of two resistors is less than the resistance of the smallest individual resistor"

The two equations: charge flow = current × time (Q = I t, coulombs = amperes × seconds) and potential difference = current × resistance (V = I R). The definitions behind them: "Electric current is a flow of electrical charge," its size being "the rate of flow of electrical charge"; and "the greater the resistance of the component the smaller the current for a given potential difference."

How to draw a circuit diagram

1. Ruler. Every wire is a straight line; corners are right angles; the circuit is a rectangle unless there is a reason otherwise.
2. The supply (cell or battery) on one side, long line positive.
3. Components on the lines, not floating beside them, each drawn with its standard symbol and nothing else (no pictures of bulbs).
4. Branches for parallel components drawn as separate loops joined at junctions marked with a dot.
5. Meters last: ammeter in the loop whose current you want, voltmeter across the component whose potential difference you want.
6. Label values (6 V, 10 Ω) next to the symbols.

Worked examples

1. A 6 V battery with two identical lamps in series. Same current in both; each lamp gets 3 V.
2. The same battery with the two lamps in parallel. Each lamp gets 6 V (brighter than in series); the battery supplies the sum of the two currents.
3. A current of 2 A flows through a 6 Ω resistor. V = I R = 12 V.
4. A current of 0.5 A flows for 2 minutes. Q = I t = 0.5 × 120 = 60 C.
5. A 4 Ω and an 8 Ω resistor in series. R total = 12 Ω; in parallel the total is below 4 Ω (and is 8/3 Ω, which GCSE does not require).
6. An LED is connected the wrong way round. No current flows; it stays dark. Turn it round.
7. Which component makes a street light switch on at dusk? An LDR: its resistance rises as the light fades, and the circuit uses the change to switch the lamp.

The mistakes that lose marks

• Voltmeter in series or ammeter in parallel.
• A cell drawn with two lines the same length, or a battery drawn as one cell.
• Pictures instead of symbols (a drawn light bulb for a lamp).
• Freehand wires with rounded corners.
• Writing that the current is "used up" in a series circuit: it is the same everywhere in the loop; it is the potential difference that is shared.
• Saying a thermistor's resistance rises with temperature: it falls.

Where to get help

If the method is not sticking from a page, a 1-on-1 online class fixes it faster than another worksheet: one tutor with a master's degree, one child, on a shared whiteboard, in your time zone (7 am before school, after 4 pm and weekend mornings, US time; after-school slots for the UK, Canada, Australia and the UAE), for about US$10 to $13 an hour. The first 30-minute class is free: how 1-on-1 online tutoring works.

Related pages

• The physical constants table: epsilon naught, the electron mass and the rest
• Light energy and the types of waves
• Potential energy: gravitational and elastic

Questions parents ask

See how we teach this, 1-on-1 online →