This how it works covers Why Power Matters in Electrical Circuits within Power for GCSE Physics. Revise Power in Energy for GCSE Physics with 14 exam-style questions and 25 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 4 of 12 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
⚙️ Why Power Matters in Electrical Circuits
For electrical devices, power can also be calculated using voltage and current. This is important because electricity bills are based on the energy used — and energy used depends on both power and time.
P = I × V Power (W) = Current (A) × Voltage (V)
Rearranging gives us more useful forms:
- P = I²R — useful when you know current and resistance
- P = V²/R — useful when you know voltage and resistance
In domestic settings, energy companies charge by the kilowatt-hour (kWh):
Energy (kWh) = Power (kW) × Time (h)
For example, a 3 kW kettle running for 0.05 hours (3 minutes) uses: 3 × 0.05 = 0.15 kWh of electrical energy.
Practice questions for Power
Which of the following is the correct definition of power?
State what is meant by the term 'power' in physics and state its unit.