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P1: Quiz 8 – Answers
P1: Quiz 8 – Answers
1) Energy cannot be created or destroyed. Instead, energy is transferred usefully, stored or dissipated (wasted)
2) Thermal energy (heat)
3)
a) A frictional force is created when parts move past each other. This frictional force causes energy to be transferred to the thermal energy stores of the moving parts, which results in the moving parts getting hot. The parts getting hot is not useful, so energy is being wasted
b) Lubricating moving parts makes it easier for the moving parts to pass each other. This reduces the frictional forces between the moving parts which reduces the energy transferred to the thermal energy stores of the parts, thus reducing unwanted energy transfer
4)
a) Conduction of thermal energy is where particles with more energy in their kinetic energy stores (hotter particles) pass on some of their kinetic energy to neighbouring particles by vibrating and knocking into them
b) Thermal conductivity measures how quickly thermal energy is transferred through a material
5)
a) Convection is when particles that have more energy in their kinetic energy stores (hotter particles) move around faster which increases the distances between the particles. This results in the density of the particles with more kinetic energy decreasing, which means that the particles with more kinetic energy (hotter particles) rise above denser cooler regions where the particles have less kinetic energy (colder particles); these hotter particles rise up and take their energy with them. Cooler particles then replace the hotter particles that have just risen, which creates convection currents
b)
i) Convection does not occur in solids as the particles cannot move
ii) Convection does occur in liquids as the particles can move
iii) Convection does occur in gases as the particles can move
c)
2) Thermal energy (heat)
3)
a) A frictional force is created when parts move past each other. This frictional force causes energy to be transferred to the thermal energy stores of the moving parts, which results in the moving parts getting hot. The parts getting hot is not useful, so energy is being wasted
b) Lubricating moving parts makes it easier for the moving parts to pass each other. This reduces the frictional forces between the moving parts which reduces the energy transferred to the thermal energy stores of the parts, thus reducing unwanted energy transfer
4)
a) Conduction of thermal energy is where particles with more energy in their kinetic energy stores (hotter particles) pass on some of their kinetic energy to neighbouring particles by vibrating and knocking into them
b) Thermal conductivity measures how quickly thermal energy is transferred through a material
5)
a) Convection is when particles that have more energy in their kinetic energy stores (hotter particles) move around faster which increases the distances between the particles. This results in the density of the particles with more kinetic energy decreasing, which means that the particles with more kinetic energy (hotter particles) rise above denser cooler regions where the particles have less kinetic energy (colder particles); these hotter particles rise up and take their energy with them. Cooler particles then replace the hotter particles that have just risen, which creates convection currents
b)
i) Convection does not occur in solids as the particles cannot move
ii) Convection does occur in liquids as the particles can move
iii) Convection does occur in gases as the particles can move
c)
6) Any 3 from the following:
- Loft insulation – this is a layer of fibreglass wool underneath the floorboards in the loft. The insulation has a low thermal conductivity, which means that there is very little conduction from the floor below the loft to the loft. This means that the floor in the loft is colder, which reduces convection currents in the loft. Loft insulation is fairly cheap.
- Double glazing – double glazing is made out of 2 layers of glass with a gap of air in the middle. The gap of air reduces the amount of conduction through the window. Double glazing is fairly expensive.
- Curtains – windows are in contact with the outside and are considerably colder than the inside of the room. If there were no curtains, the windows would cause the temperature of the room to decrease because of conduction and convection. Curtains provide an air buffer against the cold glass in the windows, thus reducing the amount of heat loss through conduction. Curtains are cheap and provide a significant saving.
- Cavity wall insulation – the exterior walls of homes are made out of 2 walls with an air gap in between the two walls known as a cavity. We can fill the cavity with insulation that has a very low thermal conductivity. The insulation reduces the amount of heat that is lost through conduction and convection in the cavity. Cavity wall insulation is quite expensive.
- Draught proofing – this reduces heat loss through convection. Draught proofing is making sure that all draughts are prevented from coming inside the house. Draught proofing is fairly cheap.
Questions
1) What is the law of conservation of energy?
2) What is the usual wasted energy store that energy is transferred to?
3) We can reduce unwanted energy transfer by lubricating moving parts.
a) Why would we want to lubricate moving parts?
b) Discuss how lubricating moving parts reduces unwanted energy transfer.
4)
a) Explain conduction.
b) What does the thermal conductivity of a material measure?
5)
a) Explain convection.
b) Does convection occur in the following states? Explain your answers.
i) Solid
ii) Liquid
iii) Gas
c) The diagram below shows a heater in a room.
1) What is the law of conservation of energy?
2) What is the usual wasted energy store that energy is transferred to?
3) We can reduce unwanted energy transfer by lubricating moving parts.
a) Why would we want to lubricate moving parts?
b) Discuss how lubricating moving parts reduces unwanted energy transfer.
4)
a) Explain conduction.
b) What does the thermal conductivity of a material measure?
5)
a) Explain convection.
b) Does convection occur in the following states? Explain your answers.
i) Solid
ii) Liquid
iii) Gas
c) The diagram below shows a heater in a room.
Draw the convection current in the air produced by the heater.
6) Give 3 ways that households can reduce the amount of heat lost from their homes. Briefly explain what the ways are, how the ways reduce the amount of heat lost from a home and comment on the cost.
6) Give 3 ways that households can reduce the amount of heat lost from their homes. Briefly explain what the ways are, how the ways reduce the amount of heat lost from a home and comment on the cost.