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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 the filament lamp converts 15% of the electrical energy it receives into useful energy, specifically light. In numerical terms, for every 100 J of electrical energy supplied to the lamp, it effectively uses 15 J to produce light. The remaining 85 J represents energy that is not transformed into useful energy, therefore it is wasted, primarily in the form of heat.
Step 2
Draw a labelled energy flow diagram to show what happens to 100 J of electrical energy supplied to the lamp.
Answer
To illustrate this, the energy flow diagram can be represented as follows:
-
Electrical Energy Supplied (100 J)
- This is the total energy entering the lamp.
-
Useful Energy Output (Light)
- Light Output: 15 J (15% of input)
-
Wasted Energy Output
- Heat: 85 J (85% of input)
The diagram would have arrows showing the flow of 100 J into the lamp, with splits showing 15 J going to useful light energy and 85 J being wasted as heat.