Brainlag PlusE = Pt and E = QV, energy in kilowatt-hours, and working out what it costs to run an appliance.
Two ways to find the energy
Energy transferred depends on how fast it goes (power) and for how long:
energy transferred = power × time
E = P × t
Energy in joules (J), power in watts (W), time in seconds (s). You can also count the charge: each coulomb that passes through a p.d. of 1 V transfers 1 J, so:
energy transferred = charge flow × potential difference
E = Q × V
Energy in J, charge in coulombs (C), p.d. in V. Recall both (AQA, Edexcel and OCR).
- A 1500 W hairdryer is used for 4 minutes
- t = 4 × 60 = 240 s
- E = 1500 × 240 = 360 000 J = 360 kJ
Minutes into seconds (× 60) before you multiply, and kJ is J ÷ 1000.
The rest of this lesson and its 9 practice questions are in Plus.
Screen 1 of 4, free to read.
- 9 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards