Basics of electricity (AQA A-Level Physics): Revision Notes

5.1.1 Basics of electricity

Key Concepts of Electricity

1. Electric Current ($I$)

• Definition: Electric current is the flow of charge per unit time, essentially describing the rate at which charge moves through a conductor.
• Formula:

$$I = \frac{\Delta Q}{\Delta t}$$

Where:

• $I$ = current (measured in amperes, $A$),
• $\Delta Q$ = charge passing through a point (measured in coulombs, C),
• $\Delta t$ = time taken for the charge to pass (measured in seconds, $s$).
• Explanation: Current is the amount of electric charge flowing past a point per second. Higher current means more charge is passing each second.

2. Potential Difference ($V$)

• Definition: Potential difference (often called voltage) is the energy transferred per unit charge between two points in a circuit. It represents the work done to move a charge from one point to another.
• Formula:

$$V = \frac{W}{Q}$$

Where:

• $V$ = potential difference (measured in volts, $V$),
• $W$ = energy transferred (measured in joules, $J$),
• $Q$ = charge (measured in coulombs, $C$).
• Explanation: Voltage can be thought of as the "push" provided to charges, helping them move through the circuit. A higher potential difference means more energy is provided to each coulomb of charge.

3. Resistance (R)

• Definition: Resistance is a measure of how much a component in a circuit opposes the flow of charge. It indicates how difficult it is for current to pass through a material.
• Formula:

$$R = \frac{V}{I}$$

Where:

• $R$ = resistance (measured in ohms, $\Omega$ ),
• $V$ = potential difference across the component (volts, $V$),
• $I$ = current through the component (amperes, $A$).
• Explanation: Resistance affects the current for a given potential difference. Components with higher resistance allow less current to pass for the same voltage.