P2: ENERGY TRANSFER BY HEATING
Energy Transfer by Conduction
Metals are the best conductors of energy
Non-metal materials such as wool and fibreglass are the best insulators
The higher the thermal conductivity of a material, the higher the rate of energy transfer through it
The thicker a layer of insulating material, the lower the rate of energy transfer through it
Infrared Radiation
All objets emit and absorb infrared radiation
The hotter an object is, the more infrared insulation it emits in a given time
Blackbody radiation is radiation emitted by a body that absorbs all the radiation incident on it
The temperature of an object increases if it absorbs more radiation than it emits
The Earth's temperature depends on a lot of factors, including the absorption of infrared radiation from the Sun, and the emission of radiation from the Earth's surface and atmosphere
Specific Heat Capacity
The specific heat capacity of a substance is amount of energy needed to change the temperature of 1kg of the substance by 1°C
energy needed = mass x specific heat capacity x temperature change
The greater the mass of an object,the more slowly its temperature increases when it is heated
Heating and Insulating Buildings
Electric and/or gas heaters and gas or oil-fired central heating or solid-fuel stoves are used to heat houses
The rate of energy transfer from houses can be reduced by using:
loft insuation
cavity wall insulation
double-glazed windows
aluminium foil behind radiators
external walls with thicker bricks and lower thermal conductivity
Cavity wall insulation is insulation material that is used to fill the cavity between the two brick layers of an external house wall