Physics: Chapter 4 Revision - Electric Circuits

Current: Flow of charge of electrons

Size of current: Rate of flow of charge per second

I = Q/t  current, A = charge flow, C / time, s

Electrons have a negative charge. They flow towards the positive side in a circuit.

Diodes only allow current to flow in one direction. This prevents any damage to a circuit if the current flows in the wrong direction.

In a series circuit, the current is the same all around the circuit.

Potential difference: The energy transferred to a component, or the work done on a component by each coulomb of charge that flows through it

V = E/Q  potential difference, V = energy transferred, J / charge flow, C

A voltmeter measures the potential difference of a component, in volts. Voltmeters have to be connected in parallel with the component they are measuring.

R = V/I  resistance, Ω = potential difference, V / current, A

Resistance is caused by vibrating ions inside a wire, which makes it harder for the electrons to pass through. A resistor in a circuit affects the current in both series and parallel circuits.

Ohm's law: The current through a resistor (at a constant temperature) is directly proportional to the potential difference across it.

Filament Lamp : Resistance increase if temperature increases

Diode : Forward resistance low; reverse resistance high

Thermistor : Resistance decreases if temperature increases

LDR : Resistance decreases if light intensity increases

In a series circuit, the same current passes through each component.

The total potential difference from the power supply is shared between the components.

The total resistance of the components is the sum of the resistance of each component.

Adding additional resistors in series circuits decreases the current and increases the total resistance.

In this series circuit, R₁ + R₂ = total resistance

In parallel circuits, the total current through the circuit is the sum of the currents through each branch of the circuit.

The potential difference through the components in parallel is the same.

I = V/R Current, A = potential difference, V / component resistance, Ω

The more components that are added in parallel, the less the total resistance of the circuit, as each component adds more current and resistance, but the voltage stays the same.