A family uses a wood-burning stove in a poorly insulated cottage. Fig. 1 shows an infrared image represented by arrows leaving the stove, walls and single-g...
Question 1 Report
A family uses a wood-burning stove in a poorly insulated cottage. Fig. 1 shows an infrared image represented by arrows leaving the stove, walls and single-glazed window. The room reaches a comfortable temperature, but the family burns a large mass of logs each week. They are deciding whether to fit loft insulation or buy a larger stove.
(a) What type of energy transfer occurs through the loft insulation? [1]
(b) Describe how loft insulation reduces the rate of energy transfer. [2]
(c) Which change is most likely to reduce the mass of logs burned each week: fitting loft insulation or buying a larger stove? Give a reason. [2]
This power station is built beside a forest-products factory and uses dry wood chips that would otherwise be discarded. Fig. 1 shows a fuel store feeding a boiler. Steam from heated water turns a turbine linked to a generator. The factory claims that this biomass resource is renewable because new trees are planted each year. A fan supplies air so that the fuel burns completely.
(a) What gas is needed for complete combustion in the boiler? [1]
(b) Draw one arrow on Fig. 1 to show the useful energy transfer from the turbine to the generator. [1]
(c) Explain why biomass can be described as renewable, but may still contribute to global warming. [3]
Answer Details
Insulating the cottage
(a) Thermal energy transfer through loft insulation is by conduction. [1]
(b) Insulation contains trapped air. Air is a poor conductor, and trapping it also reduces convection currents, so the rate of thermal energy transfer falls. [2]
(c) Fitting loft insulation is more likely to reduce the mass of logs burned. It reduces energy loss from the house, so less chemical energy from the logs is needed to maintain the room temperature. [2]
Biomass power station
(a) Complete combustion requires oxygen. [1]
(b) The useful transfer is mechanical, or kinetic, energy from the turbine to the generator. [1]
(c) Biomass can be renewable because new plants can be grown to replace the fuel and absorb carbon dioxide by photosynthesis. However, burning biomass releases carbon dioxide, which absorbs infrared radiation and increases the greenhouse effect. [3]
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