1.8 Specific Heat Capacity

Transcription

1 1.8 Specific Heat Capacity Questions on energy transfers and insulation 46 minutes 46 marks Answer all questions. Write in pen, draw in pencil. If you have any problems please come and see me before the homework is due. Page 1 of 13

2 Q1. The diagrams show the cross-section of three double glazed windows. The gap between the two sheets of glass can be filled with either air or a mixture of air and argon. The U-values for different types of double glazed windows, using different types of glass X and Y, are given in the table. The larger the U-value; the greater the energy loss through the window. Type of window 12 mm gap 16 mm gap 20 mm gap 1 Glass type X with air Glass type X with air and argon Glass type Y with air Glass type Y with air and argon (a) Which type of window, 1, 2, 3 or 4 is the least energy efficient?... (b) Which two windows should be compared to decide if adding argon to the gap improves the energy efficiency of the window? Window...and window.... Page 2 of 13

3 (c) A householder is going to buy new windows. The sales assistant recommends the householder to buy windows with a 20 mm gap. These windows are much more expensive than those with a 16 mm gap. Is it worth the householder paying the extra cost to buy 20 mm windows rather than 16 mm windows? Draw a ring around your answer. Yes / No Explain, in terms of energy efficiency, the reason for your answer (d) Windows are given an energy rating, from A down to G. The diagram shows the energy label from one type of double glazed window. All new double glazed windows must have an energy rating of C or above. Windows having a C rating have a U-value of 1.9. Which windows given in the table would the householder be unable to buy?... (ii) Which statement gives the reason why this type of label is useful to a householder who is going to buy new windows? Put a tick ( ) in the box next to your answer. Can compare the cost of different windows. Can compare the energy efficiency of different windows. Can see which window would look best. Page 3 of 13

4 (iii) Changing old windows for new ones will reduce a householder s energy bills by 100 a year. New windows will last 30 years before they need replacing. Assuming energy costs stay the same, how much will the householder save over the lifetime of the windows? Show clearly how you work out your answer Total savings =... (Total 7 marks) Q2. (a) The diagram shows how much heat is lost each second from different parts of an uninsulated house. Each year, the house costs 760 to heat. How much money is being wasted because of heat lost through the roof? Show clearly how you work out your answer. Page 4 of 13

5 (ii) Insulating the loft would cut the heat lost through the roof by 50 %. The loft insulation has a payback time of years. How much did the loft insulation cost to buy? Cost of loft insulation =... (b) What happens to the wasted energy? (Total 4 marks) Q3. (a) The graph shows the temperature inside a flat between 5 pm and 9 pm. The central heating was on at 5 pm. What time did the central heating switch off?. Page 5 of 13

6 (ii) Closing the curtains reduces heat loss from the flat. What time do you think the curtains were closed?. Give a reason for your answer.. (b) Less heat is lost through double-glazed windows than through single-glazed windows. Complete the following sentences by choosing the correct words from the box. Each word may be used once or not at all. conduction conductor convection evaporation insulator radiation Air is a good.... When trapped between two sheets of glass it reduces heat loss by... and... (3) (c) The table gives information about three types of house insulation. Type of insulation Cost to install Money save each year on heating bills Payback time Double glazing years Loft insulation years Cavity wall insulation Page 6 of 13

7 Use the information in the table to calculate the payback time for cavity wall insulation.. (ii) Explain why people often install loft insulation before installing double glazing or cavity wall insulation..... (Total 9 marks) ## (a) The table gives information about some ways of reducing the energy consumption in a house. Method of reducing energy consumption Installation cost in Annual saving on energy bills in Fit a new hot water boiler Fit a solar water heater Fit underfloor heating Fit thermostatic radiator valves Which way of reducing energy consumption is most cost effective over a 10-year period? To obtain full marks you must support your answer with calculations. (3) Page 7 of 13

8 (b) Explain why using an energy-efficient light bulb instead of an ordinary light bulb reduces the amount of carbon dioxide emitted into the atmosphere. (Total 5 marks) Q5. (a) The diagram shows an immersion heater used to heat water inside a tank. Heat is transferred through the water by convection. (ii) Draw arrows on the diagram to show the movement of the water in the tank when the heating element is switched on. Explain how a convection current is set up in the water. The explanation has been started for you. When the heating element is switched on, the hot water nearest the element rises because... Page 8 of 13

9 (b) The diagram shows two ways to reduce heat loss through the walls of a house. How is the aluminium foil able to reduce heat loss? (ii) The plastic foam is good at reducing heat loss through the walls. Explain why. (3) (c) Evaporation is an important heat transfer process. When sweat evaporates, it takes heat energy from your body. As humidity increases, you are more likely to feel hot and uncomfortable. Explain why (Total 10 marks) Page 9 of 13

10 Q6. The drawing shows parts of a house where it is possible to reduce the amount of energy lost. (a) Give one way in which the amount of energy lost can be reduced from each of the following parts of the house. 1, 2 and (3) (b) Energy consumption can be reduced by using a more efficient boiler or more efficient light bulbs. What is meant by a more efficient light bulb? (Total 4 marks) Page 10 of 13

11 Q7. (a) The diagram shows the ways in which heat energy can be transferred from an old house. Calculate the percentage of energy transferred by draughts. % energy transferred by draughts =... (ii) Complete the following sentence using one of the words from the box. conduction convection radiation Draughts transfer heat energy by... (iii) State one way of reducing the heat transfer by draughts.. Page 11 of 13

12 (b) The diagram shows a section through the walls of a house built in Explain how the air cavity between the two walls reduces the heat transfer from the house. (c) The table shows the installation costs and yearly savings on energy bills for different methods of insulating a house. Method of insulation Installation cost in Yearly saving on energy bills in Double glazing Loft insulation Cavity wall insulation Give one reason why loft insulation is often fitted to an old house before double glazing or cavity wall insulation... (ii) The time it takes for the saving on energy bills to equal the cost of installing the insulation is called the pay-back time. Calculate the pay-back time for loft insulation.. Pay-back time =... years (Total 7 marks) Page 12 of 13

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