Log in
Module 4: Electrons, waves, and photons›Circuit symbols (4.2.1)

Circuit symbols (4.2.1)

Standard circuit symbols and diagrams for cells, resistors, diodes, LEDs, thermistors, LDRs, and other components in A-level Physics.
5 min

On this page

Circuit symbols are graphical representations that represent electrical components in a circuit. Some of the essential circuit symbols are shown below.

Open switch, Closed switch, Cell, Battery, Diode, Resistor, Variable resistor, LED, Lamp, Fuse, Voltmeter, Ammeter, Thermistor, LDR, Motor

It is important that you are able to recall the name and function of these circuit components for your exams.

Add to favourites

The circuit symbols of a cell and a battery are shown below.

Illustration showing a Battery on the left with positive and negative terminals, and a Cell on the right with positive and negative terminals, along with a dotted line connecting the components.
  • Cell: Provides the circuit with a source of electrical energy.
  • Battery: Two or more cells connected in series.

Each cell has two terminals. One side of the cell is the positive terminal (+) and the other is the negative terminal (−). When a circuit is closed, electrons flow away from the negative terminal towards the positive terminal.

However, current was originally defined as flowing from the positive terminal to the negative terminal, and this definition has stuck. This is known as conventional current.

Add to favourites

The circuit symbols of an open switch, a closed switch, and a fuse are shown below.

Open switch, Closed switch, Fuse © Medify
  • Switch: Turns a circuit on (closed) or off (open).
  • Fuse: Breaks the circuit when the current exceeds a given value.
Add to favourites

The circuit symbols of a voltmeter and an ammeter are shown below.

A diagram showing a voltmeter labeled 'V' on the left and an ammeter labeled 'A' on the right, with the words 'Voltmeter' and 'Ammeter' underneath each respective symbol.
  • Voltmeter: Measures the potential difference across an electrical component.
    It is connected in parallel.
  • Ammete: Measures the current in an electrical wire.
    It is connected in series.
Add to favourites

The circuit symbols of a fixed resistor, a variable resistor, a light-dependent resistor (LDR), and a thermistor are shown below.

Diagrams of different types of resistors: Fixed resistor, Variable resistor, LDR, and Thermistor.
  • Fixed resistor: An electronic device that provides a constant resistance value in a circuit. It can be used to control the flow of current in a wire branch.
  • Variable resistor: A component that allows the resistance to be manually adjusted. It can be used to control the voltage across the variable resistor.
  • Thermistor: A temperature-sensitive resistor whose resistance varies significantly with temperature.
  • Light-dependent resistor (LDR): A light-sensitive resistor whose resistance varies significantly with light intensity.
Add to favourites

The circuit symbols of a diode and a light-emitting diode (LED) are shown below.

A diagram showing two types of electronic components. On the left, a symbol for a Diode is depicted, and on the right, a symbol for an LED (Light Emitting Diode) is shown with arrows indicating light emission.
  • Diode: A semiconductor device that allows current to flow in one direction only, while blocking it in the opposite direction.
  • Light-emitting diode (LED): A semiconductor device that emits light when current travels through it in a specific direction.
Add to favourites

The circuit symbols of a lamp and a capacitor are shown below.

A diagram showing two electrical symbols: on the left, a red circle with a cross inside labeled 'Lamp', and on the right, two parallel lines with a gap labeled 'Capacitor'.
  • Lamp: A device that converts electrical energy into light energy.
  • Capacitor: A device that stores electrical energy.
Add to favourites

The key functions of major electrical components are summarised below.

A table displaying electronic components and their functions. The elements listed are: Switch - Turn a circuit on (closed) and off (open); Cell - Provides the circuit with a source of electrical energy; Battery - Two or more cells connected in series; Diode - A semiconductor device that allows current to flow in one direction only, while blocking it in opposite direction; Resistor - An electronic device that provides a constant resistance value in a circuit; Variable resistor - A component that allows the resistance to be manually adjusted; Light-emitting diode (LED) - A semiconductor device that emits light when current travels through it in a specific direction; Lamp - A device that converts electrical energy into light energy; Fuse - Breaks the circuit when the current exceeds a given value; Voltmeter - Measures the potential difference across an electrical component; Ammeter - Measures the current in an electrical wire; Thermistor - A temperature-sensitive resistor whose resistance varies significantly with temperature; Light-dependent resistor (LDR) - A light-sensitive resistor whose resistance varies significantly with light intensity; Motor - A device that converts energy into mechanical energy.
Add to favourites

A circuit diagram uses standardised symbols to visually represent an electrical circuit.

Circuit diagrams can include a variety of electrical components, ranging from simple setups that consist of a cell, wires, and a resistor to more complex designs that feature combinations of resistors, capacitors, thermistors, and other elements.

A circuit diagram featuring symbols for voltage (V) and current (A). The diagram includes two voltage sources at the top and bottom, with multiple current indicators (A) connected through resistors.

Rules for circuit diagrams:

  1. Use horizontal or vertical lines to represent wires only.
  2. Use the standardised circuit symbols.
  3. Do not leave any gaps between wires.

Drawing the direction of the current flow can be helpful, but is not essential. Current flows from the positive terminal to the negative terminal of the cell or battery.

Add to favourites

For a circuit to be operational, it must include:

  1. a power source (i.e. a cell or battery)
  2. a closed path for the current to flow
  3. electrical components (e.g. resistors, capacitors, thermistors, etc.)

It is important to note that connecting a battery directly to a wire, without any other components, can cause the battery to short-circuit. Wires have very low resistance, which allows a high current to flow through them when a voltage is applied.

Add to favourites

The simple circuit below consists of a cell, an ammeter, and a resistor.

  • The battery serves as a power source, providing electrical energy to drive electrons around the circuit.
  • The ammeter measures the current travelling through the wires.
  • The resistor is used to control the amount of current travelling through the circuit.

It is important to note that some of the electrical energy travelling through the resistor and wires is dissipated as heat.

A simple electrical circuit diagram featuring a battery symbol, a resistor represented by a rectangle, and a current symbol labeled 'A'.

This simple circuit setup enables you to measure the current flowing through a resistor when a specific voltage is applied by the battery. This can be used to measure voltage if the resistance is known, or to measure resistance if the voltage is known.

Add to favourites

The simple circuit below consists of a cell, a switch, and a lamp.

  • The battery serves as a power source, providing electrical energy to drive electrons across the circuit.
  • The switch prevents current from flowing through it when it is closed.
  • The lamp converts electrical energy into light energy.
A simple circuit diagram featuring a battery, a switch, and a light bulb. The battery is represented at the top left, with a switch next to it. The circuit connects to a light bulb at the bottom center, which has an 'X' inside it, indicating it is off. The diagram is outlined in red on a light gray background, with the © Medify logo at the bottom.

This simple circuit setup enables a light to be turned on and off using a switch.

Add to favourites