Thermal physics

Pure ice at its melting temperature is heated steadily. Some ice melts, but the temperature remains constant. Which statement best explains the observation?

1. A

   No energy enters because the temperature is constant.

2. B

   Energy increases particle potential energy as the solid structure changes.

3. C

   The particles stop moving while melting.

4. D

   The energy is destroyed by the phase change.

1. a

   Select and explain Select the best explanation and distinguish internal energy from temperature.

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   Correct choiceB

   1. 1

      Selects option B: melting increases particle potential energy while the structure changes.

   2. 2

      Explains that energy is transferred into the ice even though temperature is constant.

   3. 3

      Explains that the energy changes particle arrangement or potential energy rather than increasing average kinetic energy during melting.

An insulated 0.50 kg metal block is heated electrically. A joulemeter measures energy supplied. The block begins at 20.0 °C.

1. a

   Describe Describe the relationship between energy supplied and temperature rise.

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   1. 1

      States that temperature rise is approximately directly proportional to energy supplied.

   2. 2

      Supports the claim with the near-constant increase of about 4.8 °C for each 2000 J.

2. b

   Calculate Use the full data range to estimate the metal's specific heat capacity.

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   1. 1

      Finds temperature rise = 39.1 − 20.0 = 19.1 °C.

   2. 2

      Uses c = Q ÷ (mΔT).

   3. 3

      Obtains c = 8000 ÷ (0.50 × 19.1) ≈ 838 J kg⁻¹ K⁻¹.

3. c

   Evaluate The accepted value is 800 J kg⁻¹ K⁻¹. Explain one likely reason for the higher experimental value and propose a specific improvement.

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   1. 1

      Identifies a relevant effect such as energy heating the surroundings, heater, or temperature sensor rather than only the block.

   2. 2

      Explains that treating all supplied energy as block energy while the measured temperature rise is reduced makes Q ÷ (mΔT) overestimate c.

   3. 3

      Proposes a linked improvement such as better insulation and a lid, embedding the heater and probe well, or determining the apparatus heat capacity.

A food-delivery team wants to compare felt, bubble wrap, and corrugated card as insulation around identical cups. Available equipment includes cups with lids, thermometers, measuring cylinders, a kettle, a stopwatch, elastic bands, and equal-thickness samples of each material.

1. a

   Formulate Write a focused research question and a testable hypothesis with scientific reasoning.

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   1. 1

      Writes a question linking insulation material to a measured temperature change over a fixed time.

   2. 2

      States a directional, testable hypothesis identifying one material or material feature.

   3. 3

      Justifies the hypothesis using conduction, trapped air, convection, and/or radiation appropriately.

2. b

   Design Describe a safe method that makes the comparison valid and produces sufficient data.

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   1. 1

      Controls water volume, starting temperature, cup and lid, insulation area and thickness, room conditions, and measurement duration.

   2. 2

      Measures temperature at regular times for every material and an uninsulated control, with repeats or simultaneous trials.

   3. 3

      Includes safe handling of hot water and a consistent method for mixing or positioning the thermometer.

3. c

   Process State how the data should be processed to decide which material is best.

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   1. 1

      Calculates mean temperature change or cooling rate for each material from repeated trials.

   2. 2

      Compares results on the same temperature–time graph and considers spread or uncertainty before concluding.