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Thermal physics
5 NET Physics questions with answers and explanations.
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What is the maximum efficiency of an engine working between 600 K and 300 K?
- 1 25%
- 2 75%
- 3 50%
- 4 100%
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Correct answer: 50%
Carnot efficiency = 1 - 300/600 = 0.5, which is 50%.
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The power radiated by a hot body is proportional to its absolute temperature raised to the power of:
- 1 1
- 2 2
- 3 3
- 4 4
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Correct answer: 4
This is the Stefan-Boltzmann law: power is proportional to T^4.
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A sealed rigid container of gas is heated from 27 degrees C to 327 degrees C. By what factor does the pressure change?
- 1 It doubles
- 2 It halves
- 3 It becomes 12 times larger
- 4 It does not change
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Correct answer: It doubles
The temperatures are 300 K and 600 K. At constant volume the pressure is proportional to absolute temperature, so it doubles.
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A gas expands at a constant pressure of 1 x 10^5 Pa, and its volume increases by 2 x 10^-3 m3. How much work does it do?
- 1 50 J
- 2 100 J
- 3 200 J
- 4 2000 J
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Correct answer: 200 J
Work = P x change in volume = 10^5 x 2 x 10^-3 = 200 J.
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A 1 m metal rod lengthens by 1.2 mm when its temperature rises by 100 degrees C. What is its coefficient of linear expansion?
- 1 1.2 x 10^-5 per degree C
- 2 1.2 x 10^-3 per degree C
- 3 1.2 x 10^-2 per degree C
- 4 1.2 x 10^-7 per degree C
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Correct answer: 1.2 x 10^-5 per degree C
alpha = change in length / (length x temperature change) = 1.2 x 10^-3 / (1 x 100) = 1.2 x 10^-5 per degree C.