Specific heat capacity and specific latent heatEdexcel International A Level Physics: Subtopic test

1. 1
   A student heats 0.50 kg of water in a well-insulated beaker using a 60 W immersion heater. The specific heat capacity of water is 4180 J kg⁻¹ K⁻¹. The heater is switched on for 520 s.

   (a)

   The temperature of the water rises by 15 K. What is the energy transferred to the water?

   [1 mark]

   • A2.1 kJ
   • B63 kJ
   • C0.14 kJ
   • D31 kJ

   (b)

   How long would the 60 W heater take to supply that energy to the water if no energy were lost?

   [1 mark]

   • A520 s
   • B1.9 × 10⁶ s
   • C1.9 × 10⁻³ s
   • D8.7 s

   (c)

   The student measures a temperature rise of 12 K, not 15 K. Calculate the percentage of the electrical energy supplied that was transferred to the water.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A catering company uses ice to keep food chilled and steam to cook it. The specific latent heat of fusion of ice is 3.34 × 10⁵ J kg⁻¹ and the specific latent heat of vaporisation of water is 2.26 × 10⁶ J kg⁻¹. A cool box contains 0.30 kg of ice at 0 °C, which absorbs energy from the food at an average rate of 20 W.

   (a)

   What is the energy absorbed by the ice as it melts completely at 0 °C?

   [1 mark]

   • A1.1 × 10⁶ J
   • B1.0 × 10⁵ J
   • C3.3 × 10⁵ J
   • D9.0 × 10⁻⁷ J

   (b)

   How long does the ice take to melt completely if it absorbs energy at 20 W?

   [1 mark]

   • A2.0 × 10⁶ s
   • B2.0 × 10⁻⁴ s
   • C5.0 × 10³ s
   • D5.0 × 10⁴ s

   (c)

   Calculate the energy released when 0.040 kg of steam at 100 °C condenses to water at 100 °C.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student determines the specific latent heat of vaporisation of water. A beaker of water is placed in an insulated container on a top-pan balance, and a 12.0 V electric heater with an ammeter in series is lowered into the water. Once the water is boiling steadily, the student records the balance reading and switches the heater on for a measured time, then records the balance reading again.

   (a)

   The ammeter reads 4.20 A and the heater is on for 300 s. The balance reading falls by 6.0 g. Calculate the specific latent heat of vaporisation of water from these results.

   [3 marks]

   (b)

   The accepted value is 2.26 × 10⁶ J kg⁻¹. Suggest why the student's value is higher, and describe two improvements to the experiment.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A greenhouse heater is switched on by a control circuit when the potential difference across an NTC thermistor exceeds 3.0 V. The thermistor is connected in series with a 1.0 kΩ fixed resistor across a 6.0 V supply of negligible internal resistance. The circuit is to be calibrated so that it acts as a thermostat.

   (a)

   Describe how the circuit can be calibrated so that it acts as a thermostat which switches the heater at a chosen temperature.

   [6 marks]

   (b)

   The thermistor has a resistance of 2.4 kΩ at 12 °C, 1.0 kΩ at 18 °C and 0.60 kΩ at 25 °C. Determine whether the heater is on at 12 °C and at 25 °C, find the temperature at which the circuit switches, and determine the fixed resistance needed to make the circuit switch at 25 °C instead.

   [6 marks]

   Total for question 4: 12 marks

End of questions