Energy And Heat Flashcards
(22 cards)
What is energy and what is the unit
Energy is the capacity for doing work
Unit is Joules [J]
What is Power and what is the unit?
Power is the rate at which energy is used.
Unit is Watts [W]
Sun beam falling on a surface,why for the surface temperature increase?
Energy can flow from
Regions of high temp to regions of low temperature
Or high vapour pressure to low vapour pressure
What does the amount of heat that flows depend on? (3)
-the difference in temperature between two region
-the surface area between the regions
-the nature of the medium through which the heat flows (the wooden and menta spoon on a hot pan example)
How much is 1J/s in Watts?
1J/s=1 Watts
Example of chemical energy
Burning methane gas
Example of nuclear energy
The sun
Example of electric energy
Transfer of electrons through copper
Example of electormagnetic energy
Light and other forms of radiation
How much is 1 kWh in Joules?
3600000J or 3.6MJ
How much is 1 therm in kWh?
1 therm= 29.3 kWh
What is Conductivity?
Transfer of heat in solids and fluids.
Directly between neighbouring atoms or molecules.
What is Convection?
Heat transfer via movement of fluid (liquid and gas) such as air or water
What is the unit of Thermal Conductivity?
k=W/(mK)
What is the unit of Thermal Resistance?
R=m^2 K/W
What is the equation for therms resistivity? What js the unit
r=1/k (mk/W)
What is the unit of hc - convectiv heat transfer coefficient?
hc - W/(m^2K)
What is the unit for Convective Heat Transfer (Qc)
W/m^2
What is Latent heat?
Heat transfer that involves change of chemical state (or change of phase)
What is the latent heat of evaporation of water?
Approximately 2450 kJ/kg
What is the value of the latent heat of fusion of water (freezing/melting)?
334kJ/kg
What is “dew point temp”
Temp the air needs to be Cooled to achieve a relative humidity of 100%
