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A student has a battery-powered torch - Edexcel - GCSE Physics - Question 6 - 2017 - Paper 1
Question 6
A student has a battery-powered torch. When the lamp in the torch is lit for 10 s, 9 J of energy is transferred in a useful way and 61 J is wasted. Complete the ta... show full transcript
Worked Solution & Example Answer:A student has a battery-powered torch - Edexcel - GCSE Physics - Question 6 - 2017 - Paper 1
Step 1
Complete the table with correct energy values.
Answer
The useful energy transferred when the lamp is lit is 9 J. The wasted energy is 61 J. Therefore, the total electrical energy supplied to the lamp can be calculated as:
The table should be filled as follows:
| form of energy | amount of energy in 10 s / J |
|---|---|
| thermal (heat) | 61 |
| light | 9 |
| electrical | 70 |
Step 2
Explain why the temperature of the filament in the lamp remains the same.
Answer
The filament reaches a steady high temperature because the heat produced by electric current flowing through it balances the heat lost to the surroundings. Although electricity is continuously supplied, the temperature remains constant because the power input and power output are in equilibrium.
In other words, the heat energy generated by the electrical energy being converted into thermal energy is equal to the heat energy lost, preventing any further increase in temperature.