Detailed Notes: 5. Electricity: Paper 1: Physics A Level AQA

Electric current (I)

Electric current (I) - the flow of charge per unit time, or the rate of flow of charge.

I = ΔQ/Δt

(where Q is charge)

Potential difference (V)

Potential difference (V) - the energy transferred per unit charge between two points in a circuit.

V = W/Q

(where W is energy transferred)

Resistance (R)

This is a measure of how difficult it is for charge carriers to pass through a component, and is measured by dividing the potential difference across a component by the current flowing through it.

R = V/I

Ohm’s law

Ohm’s law states that for an ohmic conductor, current is directly proportional to the potential difference across it, given that physical conditions (e.g temperature) are kept constant.

Ohmic conductor

This component follows Ohm’s law therefore its current-voltage graph will look like a straight line through the origin. (This is provided physical conditions are kept constant).

Filament lamp

This component contains a length of metal wire, which heats up as current increases, therefore the resistance of this component increases as current increases.

Resistivity (ρ)

Resistivity (ρ) is a measure of how easily a material conducts electricity, it is defined as the product of resistance and cross sectional area, divided by the length of the material.