100 W heater is used to melt 50 g of ice at 0°C. How long should the heater be switched on? (Specific latent heat of fusion of ice is 334 J/g)
Correct answer: C. 2.8 min
- A. 28 min
- B. 16.7 min
- C. 2.8 min
- D. 167 min
Explanation
First, calculate the total heat needed: Q = mL = (50 g) × (334J/g) = 16,700 J. The heater provides power (P) of 100 W, which is 100 J/s. Time required is t = Q/P = 16,700J/100J/s=167seconds. Converting to minutes: 167 s / 60 s/min ≈2.8 minutes.
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Thermal equilibrium means that bodies in contact have the same temperature and no net heat flows between them. The topic distinguishes heat from temperature, uses the zeroth law of thermodynamics, and covers heat transfer, specific heat capacity, thermal expansion and the conditions for reaching equilibrium.
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