CIE A Level Physics: Practical Circuits: Circuit Symbols and EMF

Circuit Symbols

The diagrams that show the various circuit symbols used in circuit diagrams.

Switch

Turn the circuit on (closed), or off (open).

Fixed Resistor

A resistor that limits the flow of current and has a resistance it cannot change.

Variable Resistor

A resistor with a slider that can be used to change its resistance, often used in dimmer switches and volume controls.

Thermistor

A resistor whose resistance depends on its temperature; as temperature increases, resistance decreases and vice versa.

Light-dependent Resistor (LDR)

A resistor whose resistance depends on light intensity; as light intensity increases, resistance decreases and vice versa.

Diode

A component that allows current to flow in one direction only, used to convert AC to DC current.

Light-emitting Diode (LED)

A diode that emits light when a current passes through it, used for aviation lighting and displays.

Ammeter

A device used to measure the current in a circuit, connected in series with other components.

Voltmeter

A device used to measure the potential difference of an electrical component, connected in parallel with the component.

Electromotive Force (e.m.f)

The amount of energy transferred per coulomb of charge when charge passes through a power supply

Potential Difference

The energy transferred per unit charge, a measure of the energy transferred out of the circuit via the components.

Internal Resistance

The resistance within a power supply that causes energy dissipation, leading to a loss of voltage.

Terminal Potential Difference (V)

The voltage available in the circuit itself

Lost Volts

The voltage lost in the cell due to internal resistance

Ohm's Law

The principle stating that V = I × R, where V is voltage, I is current, and R is resistance.

e.m.f Equation

= IR + Ir

Current Calculation

= E / (R + r)