PhysicsChapter 11: Electricity

Electrical Power

Electrical power is the rate at which electrical energy is transferred or converted by a circuit component.

Formula sheet

Key equation

P=VI

P: electrical power (W)
V: potential difference (V)
I: current (A)

Key equation

P=I²R

Key equation

P=V²R

Key equation

W=Pt=VIt

Key equation

1\ kWh=3.6×10⁶\ J

Use P=VI for any component with known V and I.
Use P=I²R or P=V²R for a resistor.
The watt is one joule per second.
Appliance ratings give operating voltage and power.
Electrical energy billed commercially is measured in kilowatt-hours.

Quick solved example

A 12 V device draws 2.0 A for 5.0 min:

Key equation

P=VI=(12)(2.0)=24\ W

Key equation

t=5.0×60=300\ s

Key equation

W=Pt=(24)(300)=7.2×10³\ J

Did you understand this topic?

Your answer is saved with your learning record. It does not mark the topic as mastered.

Exam preparation

Exam Focus

Quick revision

Revision Zone

Review the key facts, formulas and checks before you move on.