Chapter 2 – Energy Transfer by Heating
2.1 – Energy Transfer by Conduction
Metals are the best conductors of thermal energy
Non- metal material such as wool and fibreglass are the best insulators of thermal energy
The higher the thermal conductivity of a material, the higher the rate of energy transfer through
the material
A thick layer of insulating material will have a low rate of energy transfer through it
The rate of thermal energy transfer through a material depends on the temperature difference
across the material, the thickness, and the thermal conductivity of the material
To reduce the rate of thermal energy transfer the material should have as low a thermal
conductivity as possible and be as thick as possible
2.2 – Infrared Radiation
All objects emit and absorb infrared radiation
The hotter an object is, the more infrared radiation it emits in a given time
Black body radiation is radiation emitted by a perfect black body (a body that absorbs all the
radiation that hits it)
Infrared radiation is part of the electromagnetic spectrum
2.3 – More About Infrared Radiation
The temperature of an object increases if it absorbs more radiation than it emits
The earth’s temperature is affected by the level of absorption of infrared radiation from the sun,
and the emission of infrared radiation from the earth’s surface and atmosphere
An object with a light, shiny outer surface emits radiation at a lesser rate than an object with a
dark, matt surface
The temperature of the earth depends on the rate at which radiation from the sun is reflected or
absorbed by the earth and the rate at which radiation is emitted from the earth
2.4 – Specific Heat Capacity
The specific heat capacity of a substance is the amount of energy needed to change the
temperature of 1 kg of the substance by 1oC
The greater the mass of an object, the more slowly its temperature increases when it is heated
Δ E=m ×c × Δθ
E :- Energy needed (Joules, J)
M :- mass (kilograms, kg)
C :- specific heat capacity (J/kg oC)
θ :- temperature change (degrees Celsius, oC)
2.5 – Heating and Insulating Buildings
Houses are heated by electric or gas heaters, oil, or gas central heating systems, or by solid fuel
in stoves or fireplaces
The rate of energy transfer from houses can be reduce by using loft insulation, cavity wall
installation, double-glazed windows, aluminium foil behind radiators and having external walls
built with thicker bricks that have a lower thermal conductivity
Cavity wall insulation is insulation used to fill the cavity between the two brick layers of an
external house wall
2.1 – Energy Transfer by Conduction
Metals are the best conductors of thermal energy
Non- metal material such as wool and fibreglass are the best insulators of thermal energy
The higher the thermal conductivity of a material, the higher the rate of energy transfer through
the material
A thick layer of insulating material will have a low rate of energy transfer through it
The rate of thermal energy transfer through a material depends on the temperature difference
across the material, the thickness, and the thermal conductivity of the material
To reduce the rate of thermal energy transfer the material should have as low a thermal
conductivity as possible and be as thick as possible
2.2 – Infrared Radiation
All objects emit and absorb infrared radiation
The hotter an object is, the more infrared radiation it emits in a given time
Black body radiation is radiation emitted by a perfect black body (a body that absorbs all the
radiation that hits it)
Infrared radiation is part of the electromagnetic spectrum
2.3 – More About Infrared Radiation
The temperature of an object increases if it absorbs more radiation than it emits
The earth’s temperature is affected by the level of absorption of infrared radiation from the sun,
and the emission of infrared radiation from the earth’s surface and atmosphere
An object with a light, shiny outer surface emits radiation at a lesser rate than an object with a
dark, matt surface
The temperature of the earth depends on the rate at which radiation from the sun is reflected or
absorbed by the earth and the rate at which radiation is emitted from the earth
2.4 – Specific Heat Capacity
The specific heat capacity of a substance is the amount of energy needed to change the
temperature of 1 kg of the substance by 1oC
The greater the mass of an object, the more slowly its temperature increases when it is heated
Δ E=m ×c × Δθ
E :- Energy needed (Joules, J)
M :- mass (kilograms, kg)
C :- specific heat capacity (J/kg oC)
θ :- temperature change (degrees Celsius, oC)
2.5 – Heating and Insulating Buildings
Houses are heated by electric or gas heaters, oil, or gas central heating systems, or by solid fuel
in stoves or fireplaces
The rate of energy transfer from houses can be reduce by using loft insulation, cavity wall
installation, double-glazed windows, aluminium foil behind radiators and having external walls
built with thicker bricks that have a lower thermal conductivity
Cavity wall insulation is insulation used to fill the cavity between the two brick layers of an
external house wall
