Edexcel GCSE Physics 1PH0
Key Concepts of Physics
Motion and Forces
Conservation of Energy
Waves
Light and the Electromagnetic Spectrum
Radioactivity
Astronomy
Energy – Forces Doing Work
Forces and Their Effects
Electricity and Circuits
Static Electricity
Magnetism and the Motor Effect
Electromagnetic Induction
Particle Model
Energy – Forces Doing Work
The watt, and calculating efficiency
- 3 things to know
- Paper 2
Overview
One watt as one joule per second, energy from power and time, and efficiency from useful and total energy or power, as a decimal or a percentage.
What you need to know
Answer each one before you reveal it.
Express the watt in terms of joules and seconds.
Calculate the energy transferred by a 60 W bulb left on for 30 s.
Questions from this subtopic
Each one with the model answer underneath.
- 1
State the energy transfer represented by a power of one watt.
Model answer
One joule transferred each second.
- 2
Express the watt in terms of joules and seconds.
Model answer
One watt is one joule per second, J/s.
- 3
A lamp is marked 12 W. State the energy it transfers in one second.
Model answer
12 J.
- 4
Calculate the energy transferred by a 60 W bulb left on for 30 s.
Model answer
Energy = 60 × 30 = 1800 J.
- 5
A machine transfers 250 J of energy each second. State its power.
Model answer
250 W.
- 6
A motor does 4500 J of useful work while 6000 J is supplied to it. Calculate its efficiency.
Model answer
Efficiency = 4500 ÷ 6000 = 0.75.
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