P = IV — Use when you know current AND voltage
P = I²R — Use when you know current AND resistance (no voltage given)
P = V²/R — Use when you know voltage AND resistance (no current given)
How these all connect (combining P = IV with V = IR):
- P = IV, substitute V = IR → P = I × (IR) = I²R
- P = IV, substitute I = V/R → P = (V/R) × V = V²/R
This deep dive covers Three Power Equations — When to Use Each within Electrical Power & Energy for GCSE Physics. Revise Electrical Power & Energy in Electricity for GCSE Physics with 15 exam-style questions and 30 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 2 of 15 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Electrical Power & Energy
What is the unit of electrical power?
A television has a power rating of 120 W and is left on for 3 hours. Calculate the energy transferred by the television in this time. Use the equation: energy transferred = power x time. Give your answer in joules.