IGCSE Physics (Extended) - Unit 4: Electricity (Full Cheat Sheet until Series and Parallel Resistance)

Current (I)

The rate of flow of electric charge.

Voltage (V) or Potential Difference

The work done per unit charge to move a charge between two points.

Resistance (R)

Opposition to the flow of current; it causes energy to be transferred as heat.

Ohm’s Law

The current through a conductor is directly proportional to the voltage across it, provided temperature remains constant.

Charge (Q)

A physical property of matter that causes it to experience a force in an electric field.

Electron flow

From negative to positive.

Conventional current

From positive to negative.

Series Circuit

A circuit where components are connected end-to-end and share the same current.

Parallel Circuit

A circuit where components are connected across the same two points and share the same voltage.

Ohm’s Law formula

V = I × R

Charge formula

Q = I × t

Voltage formula

V = I × R

Energy formula

E = Q × V or E = I × V × t

Power formula

P = V × I

Total resistance in series formula

Total R (series) = R₁ + R₂ + …

Total resistance in parallel formula

1/Rtotal (parallel) = 1/R₁ + 1/R₂ + …

Current unit

Measured in Amperes (A).

Voltage unit

Measured in Volts (V).

Resistance unit

Measured in Ohms (Ω).

Energy unit

Measured in Joules (J).

Charge unit

Measured in Coulombs (C).

Power unit

Measured in Watts (W).