## Tuesday, 23 September 2014

### Thermal Physics Questions

Specific heat capacities:
 copper 400Jkg-1K-1 iron 460Jkg-1K-1 water 4200Jkg-1K-1 ice 2100Jkg-1K-1
Specific latent heat of fusion of ice = 3·3×105Jkg-1
Molar heat capacities of a diatomic ideal gas:
Cv = 12·5J(molK)-1 and Cp = 20·8J(molK)-1
Question 18
 You are given an uncalibrated thermometer (that is, a thermometer which has no graduations on it). Explain how you would mark a centigrade scale on it.
 Your answer must include definitions of the terms “lower fixed point” and “upper fixed point”.
Question 19
 Metals expand when they are heated and contract when they are cooled.
 a) Describe briefly one problem caused by the expansion of metals. b) (i) What is a “bi-metal strip”? (ii) What is a thermostat? (iii) Explain briefly how a bi-metal strip can be used to make an electrical thermostat.
Question 20
 a) In what way is the expansion and contraction of water unusual? b) State the temperature at which water has its maximum density. c) Describe one problem caused by the unusual expansion of water and one advantage it brings
Question 21
 The specific heat capacity of water is very high. What effect does this have on the weather conditions experienced by people living on islands?
Question 22
 Draw diagrams to represent
 a) a heat engine b) a heat pump (or fridge) On the diagrams, label the work done, w, the energy taken from the source, Q1 and energy given to the sink, Q2.
Question 23
 Referring to the diagrams of the previous question: write down expressions for the thermodynamic efficiency,  of
 a) a heat engine b) a heat pump c) a fridge.