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This lamp has a wire filament that glows white hot when it is in use - Edexcel - GCSE Physics - Question 2 - 2012 - Paper 1
Question 2
This lamp has a wire filament that glows white hot when it is in use. (a) A 100 W filament lamp is 15% efficient. (i) Explain the meaning of the term 15% efficient... show full transcript
Worked Solution & Example Answer:This lamp has a wire filament that glows white hot when it is in use - Edexcel - GCSE Physics - Question 2 - 2012 - Paper 1
Step 1
Explain the meaning of the term 15% efficient.
Answer
The term '15% efficient' means that out of the total electrical energy supplied to the lamp, only 15% is converted into useful energy, which in this case is light. Therefore, for a 100 W filament lamp, it effectively uses 15 W of power for lighting purposes while wasting the remaining 85 W as heat or other forms of energy that are not useful for providing illumination.
Step 2
Draw a labelled energy flow diagram to show what happens to 100 J of electrical energy supplied to the lamp.
Answer
To create the energy flow diagram, you would start with 100 J of electrical energy supplied to the lamp. This energy can be represented as:
- 100 J electrical energy → 15 J useful energy (light)
- 85 J wasted energy (heat/other)
In the diagram, you would label the input as 'Electrical Energy (100 J)', with arrows pointing to two outputs: one arrow leading to 'Useful Energy (Light - 15 J)' and another arrow leading to 'Wasted Energy (Heat - 85 J)'.