P2 Energy transfer by heating

P2.1 Energy transfer by conduction

• Metals are the best conductor 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
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• Bildunterschrift: Roof and wall insulation inside a house

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 space of time
• Blackbody radiation is radiation emmitted by a body that absorbs all the radiation incident on it
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• Bildunterschrift: Infrared spectrum

P2.3 More about infrared radiation

• The temperature of an object increases if it absorbs more radiation than it emits
• The Earth's temperature depends on a lot of factors:
• absorption of infrared radiation from the sun
• emission of radiation from the Earth's surface and atmosphere
• some gases in the atmosphere such as water vapour, methane and carbon dioxide absorb infrared radiation from the Earth and prevent it from escaping into space
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• Bildunterschrift: How greenhouse gases keep the Earth warm

P2.4 Specific heat capacity

• The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1kg of the substance by 1 degree celcius
• The unit for specific heat capacity is J/kgᵒC
• ∆E = mc∆Ө
• The greater the mass of an object, the more slowly its temperature increases when it is heated
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• Bildunterschrift: Formula to calculate specific heat capacity

P2.5 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 insulation
• 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 fil the cavity between the two brick layers of an external house wall
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• Bildunterschrift: The effect of insulation