IB Physics HL B.1 Thermal energy transfers questions

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Question 1

Multiple choiceMedium1 mark

During a 10.0 min interval, a sample is melting at constant temperature. A 400 W heater is on for a total of 5.0 min; assume all energy supplied while it is on enters the sample. Which row gives the energy supplied by the heater and the particle behaviour during melting?

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Answer: B. The energy supplied is E=PtE=Pt using the time for which the heater is on: E=(400 W)(5.0×60 s)=1.2×105 J=120 kJE=(400\ \text{W})(5.0\times60\ \text{s})=1.2\times10^5\ \text{J}=120\ \text{kJ} During melting, the energy changes particle behaviour and arrangement while the average kinetic energy, and therefore the temperature, remains constant.
A: treats 5.0 min as 5.0 s, giving 2.0 kJ.
C: calculates the energy correctly but applies the temperature-rise model instead of recognizing a phase change.
D: uses the full 10.0 min interval as the heater-on time, giving 240 kJ.
Remember: energy can be transferred during a phase change without increasing the temperature.

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