IGCSE Physics / Current and voltage in circuits
Circuit symbols, ammeters and voltmeters revision notes
Edexcel International GCSE Physics (4PH1), chapter 7: Current and voltage in circuits, specification point SYM, 2.12. Free lesson.
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Circuit diagrams use standard symbols, and each meter must be connected in the correct way. An ammeter measures current in series, while a voltmeter measures voltage across a part in parallel.
How to recognise the main circuit symbols
Circuit symbols let you read and draw circuits clearly. Wires use straight lines and square corners. A battery is made from two or more cells, and the long line marks the positive side. A resistor is a plain rectangle. A variable resistor has an arrow through the rectangle, showing that its resistance can be changed. A fuse is a rectangle with a line running through it from end to end. A diode lets current through only in the direction its triangle points. An LED is a diode with two arrows pointing outwards, showing that it gives out light. An open switch has a gap.…
How to recognise the other symbols
Some components sense changes, provide heat or produce movement. A single cell is shown by one long line and one short line. The long line is positive. An LDR (light-dependent resistor) is a resistor in a circle, with arrows pointing in to show light falling on it. A thermistor is a resistor with a slanted line across it. Its resistance changes with temperature. A heater is a rectangle with lines across it. A motor is a circle with a capital M inside.
How to draw a clear circuit diagram
Use a ruler so that the wires are straight and the corners are square. Leave no gaps in the wires when the circuit is meant to be complete, because a gap breaks the circuit.
Where to connect an ammeter and voltmeter
An ammeter measures current, so it goes in series, in the loop where the current flows through it. A voltmeter measures voltage across a component, so it goes in parallel, joined to both ends of that part. An ammeter is drawn as a circle with a capital A. A voltmeter is drawn as a circle with a capital V. A lamp or LED lights only when current flows, so it can show that the circuit is working.
How to avoid the meter connection mistake
Do not put the voltmeter in series with the resistor. Voltage compares the two ends of a part, so the voltmeter must connect across both ends. In series, a voltmeter would almost stop the current. For current through a lamp, connect the ammeter in series with the lamp. For voltage across a lamp, connect the voltmeter in parallel, across the lamp.