Heat Flashcards
Heat energy can be transferred by conduction, convection and radiation.
Distinguish between the three methods of heat transfer.
Conduction is the transfer of heat energy in a solid by passing on kinetic energy from molecule to molecule.
Convection is the transfer of heat energy by the circulation of the heated parts of a liquid or gas.
Radiation is the transfer of heat energy as electromagnetic (EM) waves, without the need for a medium.
What is the thermometric property (i) of a thermocouple (ii) of a mercury thermometer.
(i) Length of liquid column
(ii) Electrical resistance
Heat
Heat is a form of energy and is measured in joules.
Temperature
Temperature is a measure of the hotness or coldness of an object.
Describe the operation of the heat pump.
Coolant is evaporated inside the fridge.
It takes specific latent heat of vaporisation from the inside of the fridge to do this. (This lowers the temperature of the fridge inside).
The coolant is pumped outside the fridge and is compressed into a high pressure liquid.
It releases its latent heat of vaporisation at this point to the surrounding air.
The liquid coolant is pumped back inside the fridge and the process repeats again
State two desirable physical properties of fluid used in a heat pump.
The fluid used in a heat pump would ideally have:
A low boiling point
A high specific latent heat of vaporisation.
Thermometric Property
A physical property that changes measurably and repeatedly with temperature change.
Emf
Emf is the voltage applied to an electric circuit.
What is the SI unit of temperature?
Degrees Celsius
What is the advantage of using the SI unit of temperature in scientific measurements?
The absolute temperature scale has the advantage that the temperature measured in Kelvin is directly proportional to the actual average energy of the particles, whose temperature is being measured.
Describe a labatory experiment to demonstrate the principle of operation of a thermocouple.
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Give the advantage of using a thermocouple thermometer instead of a mercury-in-glass thermometer.
Thermocouples have a number of advantages over mercury thermometers:
- They have a very wide range of temperatures at which they can operate.
- They respond very quickly to changing temperatures.
- They do not make use of such a hazardous material as mercury.
On what thermometric properties are the following based: (i) the thermocouple thermometer and (ii) the mercury-in-glass thermometer.
(i) The emf of a thermocouple
(ii) Length of liquid column
Latent heat
The latent heat of a substance is the heat energy required to change its state without a change in temperature.
Storage heaters are frequently used to heat buildings. State the principle that underlies the operation of an electrical storage heater.
- Large heat capacity
Explain why heat does not travel through solids by means of convection.
The particles cannot move freely.
Explain why snow is slow to melt as the air temperature rises above 0 degrees celsius.
The latent heat of snow is large.
How is energy transferred from the sun to earth?
Radiation
Why is it necessary to have a standard thermometer?
Due to different thermometric properties vary differently with temperature.
Give an advantage of geothermal heating system over a solar heating system.
- Geothermal system functions all the time
- Solar heating system works only during daytime
Heat capacity
The heat capacity of an object is the heat required to change its temperature by 1 kelvin.
Specific heat capacity
The amount of heat energy required to change 1kg of the substance by 1 kelvin.
Specific latent heat
The amount of heat energy required to change the state of 1kg of the substance without a change in temperature.
Specific latent heat of vaporisation
The amount of heat energy required to change 1kg of the substance from a liquid to a gas without a temperature change.
Specific latent heat of fusion
The amount of heat energy required to change 1kg of the substance from a solid to a liquid without a temperature change.
Solar constant
The amount of solar energy striking 1m^2 of the Earth’s atmosphere every second.
U-Value
The amount of heat energy that can be transmitted across 1m^2 of its surface every second, so long as there is a temperature difference of 1K each side of the material.
