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 is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. 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.
Topic position
Section 4 of 12
Practice
14 questions
Recall
25 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.