P2 Energy Transfer by Heating

Thermal conductors are materials that allow thermal energy to move through them easily. All metals are good thermal conductors.

Thermal insulators are materials that do not allow thermal energy to move through them easily. materials such as fibreglass and wool are good thermal insulators because they trap air.

The rate of thermal energy transfer through a material depends on:

• the tempreture difference across the material
• the thickness of a material
• the thermal conductivity of the material

To trduce the rate of thermal energy transfer, the insulating material should:

• have as low as a thermal conductivity as possible
• be as thick as possible

Infared waves are part of the electromagnetic spectrum. They are waveslengths a little longer than the wavelength of visible red light. We can detect infrared radiation  from our skin - it makes us feel warm.

• All objects emit (give off) infrared radiation. 
• The hotter an object is, the more infrared radiation emits in a given time.
• An object at constant tempreture emits infrared radiation at the same rate as it absorbs it.
• A perfect black body is an object that absorbs all the radiation that hits it.
• A perfect black body is also the best possible emitter of radiation. The radiation emitted from a perfect black body is called black body radiation.
• An object that has a constant tempreture emits radiation across a continueous range of wavelengths.

The Specific Heat Capacity of the substance is the ammount of energy required to raise the temprature of 1kg of the substance by 1°C (Degree Celcius).

The greater the specific heat capacity of a substance, the more energy you would need to supply to the substance in order to increase the temprature by 1°C .

you calculate the energy required to change the tempreture of a substance by a set amount,Δ0, using the equation ΔE = m x c x Δ0 where:

ΔE is the energy needed in joules, J

m is the mass of the sample in kilograms, kg

c is the specific heat capacity of the substance in joules per kilogram degrees celcius. J/kg
°C

Δ0 is the temperature change in degrees celsius,°C

People want to minimise the ammound of heat transfer from their homes in order to reduse tax

Fibreglass - loft insulation reduces the rate of energy transfer through the roof

Cavity wall insulation - reduces the rate of energy transfer through the outer walls

Aluminium foil - behind radiators reflects the infrared radiation back into the room

Double Glazing - reduces the rate of energy transfer through windows

thick bricks - reduce the rate of energy transfer through exterior walls