1.2 Conservation & Dissipation of Energy
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These flashcards are for Topic 1 - Energy in AQA GCSE Physics (Triple Higher). They cover specification points 4.1.2.1 - 4.1.2.2
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Energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed.
A system where energy and matter cannot enter or escape, meaning there is no net change to the total energy within it.
Energy that is transferred to less useful stores, often lost to the surroundings as thermal energy.
Work is done against frictional forces, which causes an increase in the internal (thermal) energy of the components.
What method can be used to reduce unwanted energy transfers due to friction between moving parts and why does this help?
Lubrication, for example by applying oil, reduces friction and therefore less energy is dissipated as heat.
By using thermal insulation.
It is a measure of how well a material conducts energy when it is heated.
What does a higher value for thermal conductivity mean?
A higher value means a higher rate of energy transfer.
The higher the thermal conductivity of a material, the _______ the rate of energy transfer by conduction across the material.
The thickness of the walls and the thermal conductivity of the materials used.
Increasing the thickness of the walls reduces the rate of cooling and therefore reduces the rate of thermal energy transfer.
Materials with low thermal conductivity should be used to reduce the rate of energy transfer.
In the thermal insulation practical, what is the independent variable?
The type of insulating material used.
In the thermal insulation practical, what is the dependent variable?
The temperature of the water.
The volume of water, the starting temperature of the water, and the mass of the insulating material.
It acts as a control to allow for comparison and to show the effect of the insulation.
To reduce energy loss to the surroundings by convection and evaporation from the water's surface.
How are the results from the thermal insulation practical used to determine the best insulator?
By plotting cooling curves; the material with the shallowest gradient is the best insulator as it has the lowest rate of cooling.
The thickness of the insulating material.
As the number of layers of insulation increases, the rate of cooling decreases.
Why does the rate of cooling of hot water in a beaker decrease over time?
The rate of energy transfer is greatest when the temperature difference between the water and the surroundings is largest; this difference decreases as the water cools.
How are the principles of thermal insulation applied in home construction to build energy-efficient houses?
By using materials with low thermal conductivity and increasing the thickness of insulation.
Define 'efficiency' in the context of energy transfers.
Efficiency is the ratio of the useful output energy transfer to the total input energy transfer.
Why is it impossible for a device to have an efficiency greater than 1 or 100%?
This would mean more useful energy is transferred than the total energy supplied, which violates the principle of conservation of energy.
What is the useful energy transfer for an electric kettle?
The transfer of thermal energy to the water.
Identify two forms of wasted energy for an electric kettle?
Thermal energy transferred to the kettle itself and its surroundings, and sound energy.
What is the useful energy transfer for a filament light bulb?
Energy transferred as light radiation.
What is the main form of wasted energy for an inefficient filament light bulb?
Energy dissipated as thermal energy (infrared radiation) to the surroundings.
State a method to increase the efficiency of boiling water in a pan?
Placing a lid on the pan reduces heat loss from the surface, increasing the efficiency of the energy transfer to the water.
State a way to increase the efficiency of an intended energy transfer in a system with moving parts?
By reducing waste output through methods such as lubrication to minimise friction.
What is the 'useful power output' of a device?
The rate at which energy is transferred into the desired or intended form.
In the thermal insulation practical, a graph of ___________ is plotted against _______.
temperature, time
What equipment is used to measure the temperature change in the thermal insulation practical?
A thermometer
What equipment is used to measure the volume of water in the thermal insulation practical?
A measuring cylinder
What feature of a house's construction reduces heat loss by having a layer of trapped gas with low thermal conductivity?
Double-glazed windows
The construction technique where insulating foam is used to fill the gap between two layers of bricks is called _______ ____ ___________.
cavity wall insulation
For a television, what are the two useful energy outputs?
Light radiation and sound radiation.
What is the primary wasted energy output of most electronic devices like televisions and computers?
Thermal energy that heats the components and is then dissipated to the surroundings.
A device is designed to waste as little energy as possible. This means it has a high _________.
efficiency
A hairdryer's useful energy outputs are thermal energy to heat the air and ________ energy of the fan.
kinetic