Heat Flashcards
What is heat?
A form of energy that causes a rise in temperature when added and a fall in temperature when withdrawn
What is the SI unit of heat?
Joule (J)
What is heat capacity?
Denoted by C, it is the heat required to change an objects temperature by 1 kelvin
What is specific heat capacity?
Denoted by c, it is the heat required to change 1kg of a substance by 1 kelvin
What is latent heat?
It is the heat required to change the state of a substance without changing its temperature
A solid changing to liquid is…
Melting
A liquid changing to solid is…
Freezing
A liquid changing to gas is…
Vaporisation
A gas changing to liquid is…
Condensation
A solid changing to gas is…
Sublimation
A gas changing to solid is…
Deposition
A gas changing to plasma is…
Ionisation
Plasma changing to gas is…
Deionization
What is specific latent heat?
Denoted by l, it is the heat required to change the state of 1kg of a substance without changing its temperature
What do heat pumps do?
They force a change of state and uses the latent heat energy for its purpose
Give two examples of heat pumps.
Perspiration and fridges
Explain perspiration.
Liquid sweat forms on the surface of the skin and evaporates. The body takes the latent heat the body’s energy level is lowered.
Explain how a fridge works.
High pressure liquid (hpl) enters an expansion mechanism which forces it to a low pressure liquid (lpl) by moving it’s particles apart. The lpl tries to change state to a low pressure vapour (lpv) and it takes the latent energy required from the fridge contents. The lpv enters a compressor which forces its particles together and becomes a high pressure vapour (hpv). The hpv tries to change state to a hpl and the latent energy it releases is given out from the back radiator fins of the fridge. The cycle repeats.
What are the three methods of heat transfer?
Conduction, convection and radiation
What is conduction?
The transfer of heat in solids by passing kinetic energy from molecule to molecule
What is convection?
The transfer of heat energy in liquids or gasses through circular currents
What is heat radiation?
The transfer of heat energy as electromagnetic waves without the need of a medium
What is the solar constant?
The amount of solar energy striking 1 square meter of the earth’s atmosphere every second, 1.37kW-²
How do solar heating panels work?
They consist of liquid filled pipes in a glass box. The dark coloured pipes absorb the sunlight which heats up the liquid.
What do photovoltaic cells do?
They convert light energy to electrical energy
What is a U-value?
An indicator of how good a substance is at transmitting heat across it.
A high U-value means the substance is…
A good conductor
A low U-value indicates the substance is…
A good insulator
What is the U-value of a substance? (Advanced)
The amount of heat energy that can be transmitted across 1 square meter of a substances surface every second
