Charge & Current

source of potential difference

Cell, battery, or electrical generator → provides voltage → push charge round circuit.

Purpose of cell/battery in a circuit

Makes one end positive and the other negative, setting up a potential difference.

Define potential difference (voltage)

Energy transferred per unit charge between two points of a circuit

Equation linking potential difference, work done, and charge

V = W
Q

Units of potential difference, work done, and charge?

Voltage (V), Joules (J), Coulombs (C)

How is potential difference measured in a circuit?

Using a voltmeter, connected in parallel across a component.

What is electric current?

The flow of electrical charge.

Unit and symbol of current

Ampere (A), symbol I

What carries current in metals?

electrons

Formula linking charge, current, and time

Q = I × t

What is 1 Coulomb (C)?

The charge that flows when 1 A current passes for 1 second.

Why do electrons flow from negative to positive in a circuit?

Electrons are negatively charged → repelled by the negative terminal → move towards the positive terminal.

What is conventional current?

Flow of positive charge from positive terminal to negative terminal.
Used before discovery of the electron.

What is electron flow?

Actual flow of electrons, from negative terminal to positive terminal.

How is current measured in a circuit?

With an ammeter, always connected in series.

Current in a closed loop series circuit and why?

The same at every point.
Reason: The same number of electrons per second flows through all parts of the circuit.