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Thermal Physics Questions Specific heat capacities:
| copper |
400Jkg-1K-1 |
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| iron |
460Jkg-1K-1 |
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| water |
4200Jkg-1K-1 |
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| ice |
2100Jkg-1K-1 |
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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 1
| A piece of metal of mass 0·2kg is heated to a temperature of 200°C. It is then put into 0·2kg of water at 20°C in a container of negligible heat capacity. The "final" temperature, after stirring, is 40°C. Calculate the specific heat capacity of the metal. |
Question 2
| A piece of ice at -20°C is put into a copper calorimeter of mass 0·2kg which contains 0·15kg of water at 20°C. The water is stirred until all the ice has melted. At this time the temperature of the water (and calorimeter) is 15°C. Calculate the mass of the piece of ice. |
Question 3
| A refrigerator is capable of removing 50J of heat per second from a container of water. How long will it take to change 2kg of water at 10°C into ice at -5°C? Assume that the rate of removal of heat remains constant and that the container has negligible heat capacity.
Are these
assumptions likely
to be valid in
practice? |
Question 4
| A piece of metal of mass 100g, has a temperature of 100°C. It is put into 100g of water at 20°C in a container of negligible heat capacity. After stirring, the maximum temperature of the "mixture" (metal and water) is 27·5°C. Calculate the specific heat capacity of the metal. |
Question 5
| How long will it take to change the temperature of 200kg of water from 15°C to 40°C, using a heater of power 3kW. Assume that all the thermal energy remains in the water. |
Question 6
| The diagram below show a cross-section view of a sheet of metal (of thermal conductivity, k) covered on each side by a layer of plastic of thermal conductivity k/1000. The lower face of the plastic is maintained at a steady temperature, T4 = 150°C. The top surface is maintained at a steady temperature, T1 = 20°C. Calculate the temperatures of the surfaces of the metal, T2
and T3. Assume that the heat lost through the sides of the metal (and plastic) is negligible. |
Question 7
| A rectangular piece of metal is 20·00cm×30·00cm, at 20°C. The linear expansivity (linear expansion coefficient) for the metal is a = 1×10-6°C-1. |
| Calculate |
| a) |
the surface area, Ao, of the piece of metal at 20°C (yes I know its difficult, but try…) |
| b) |
the lengths of the sides of the piece of metal at 80°C |
| c) |
the surface area, A, of the piece of metal at 80°C |
| d) |
the value of the quantity |
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Compare this figure with the value of a. |
Question 8
| a) |
Considering question 9 part d), define, in words, the area expansion coefficient of a substance and state how it is related to the linear expansion coefficient. |
| b) |
Suggest a definition of the volume expansion coefficient of a substance and predict how it might be related to the linear expansion coefficient. |
Question 9
| Two moles of an ideal gas are heated at a constant pressure of 105Pa. The temperature of the gas increases from 293K to 313K. |
| Calculate |
| a) |
the total amount of heat supplied |
| b) |
the change in internal energy of the gas |
| c) |
the work done by the gas during expansion |
| d) |
the change in volume of the gas. |
Question 10
| 20mols of an ideal gas are in a cylinder of initial volume 0·5m3 at a temperature of 27°C. The gas is supplied with 10000J of heat at constant pressure. Calculate |
| a) |
the final temperature of the gas |
| b) |
the final volume of the gas |
| c) |
the change in internal energy of the gas |
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© David Hoult 2008 |
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