Heat Flashcards
Heat
Is the form of energy transferred from the hotter substance to the cooler substance as a result of the temperature difference between them.
Temperature
A measure of coldness or hotness of a body
Internal Energy
The energy possessed by a body due to the random vibrations of its’ molecules.
Thermometric property
Any physical property that changes measurably with temperature
Heat Capacity
The amount of heat energy required to change an object’s temperature by 1K
Specific Heat Capacity
The heat energy required to change the temperature by 1K for a substance of 1kg
Latent Heat
The heat energy required to change an object’s state without a change in temperature.
Specific Latent Heat
Amount of heat energy needed to change the state of a 1kg substance without a change in temperature.
Specific latent heat of fusion
Amount of heat energy needed to change 1kg of a substance from a solid to a liquid without a change in temperature
Specific latent heat of vapourisation
Amount of heat energy needed to change 1kg of a substance from a liquid to a gas without a change in temperature
Convection
The circulation of heat in a fluid due to the motion of the fluid itself.
Conduction
The transfer of heat with no net movement of the medium due to a difference in temperature within the medium.
Radiation
The transfer of heat between two points by means of electromagnetic waves
Solar Constant
Average amount of the Sun’s energy falling per second perpendicularly on 1m squared on the Earth’s atmosphere.
U-value
A measure of the heat flow through 1 m2 of material each second when a temperature difference of one kelvin exists between the two sides
Why is a standard thermometer necessary?
Different thermometers based on different thermometric properties give slightly different values for the same temperature.
How many kelvin in 0 degrees celsius?
273.15 K
Give four examples of thermometric properties.
Volume of column of mercury
Emf of a thermocouple
Resistance of Wire
Colour of liquid crystals
Name one essential feature of a clinical thermometer.
Constriction
In words explain the operation of a heat pump?
- Volatile liquid called refrigerant with low boiling point flows along a pipe as shown.
- This liquid takes heat energy from the air and food inside the fridge and the liquid is vaporised to a gas.
- The air and food inside the fridge is now cooler
- The gas flows into condenser unit and is compressed back to a liquid releasing latent heat to the surrounding air.
- The cycle repeats until a certain low temperature inside the fridge is achieved which is determined by a thermostat control.
What is the function of operation of a heat pump?
A heat pump takes energy from a cooler region and transfers it to a warmer region.
How does perspiration occur?
- When we exercise are body temperature rises.
- Liquid forms on skin and is vapourised.
- Latent heat needed to vapourise so heat is taken from the body which is lowered to normal temperature.
Why does the high specific latent heat of ice make it a good coolant?
Takes in a lot of heat energy when melting.
How can an object be engineered to reduce heat loss? (3)
Add insulating lid
Lag with cotton wool
Reduce specific heat capacity of materials