Electrical Power and Energy
Power P = VI and energy E = Pt.
About this topic
Electrical power is the rate of energy transfer: P = VI = I²R = V²/R, in watts. Energy used is E = Pt, in joules, or kilowatt-hours (kWh) on bills. A 2 kW kettle running for 3 minutes uses 0.1 kWh.
At 230 V that kettle draws about 8.7 A, which is why it needs a thicker cable and a 13 A fuse. Heating in wires is I²R, which is why power lines use high voltage and low current to reduce losses: halving the current cuts the wasted heat to a quarter.
Comparing appliances' power ratings helps judge running costs and efficiency. A 10 W LED bulb gives as much light as an old 60 W filament lamp, saving about 50 W every hour it is on, and at a typical price of a few cents per kWh that adds up over a year.
Remember that a kilowatt-hour is a unit of energy, not power, and that 1 kWh equals 3.6 million joules. Power rating tells you how fast an appliance uses energy, not how much it uses in total.
Key ideas
- Unit: watt
- Kilowatt-hours bill energy
- P = I²R
Quick check
Use cases: where Electrical Power and Energy helps
- Homework: review the key idea behind Electrical Power and Energy before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Electrical Power and Energy without notes.
- Visual learning: play with the interactive lab to see how Electrical Power and Energy changes when you adjust its inputs.
- Teaching a friend: explain Electrical Power and Energy in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Electrical Power and Energy?
Power P = VI and energy E = Pt.
What will I learn in Electrical Power and Energy?
Unit: watt. Kilowatt-hours bill energy. P = I²R.
Is Electrical Power and Energy part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Electrical Power and Energy lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Electrical Power and Energy?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.