P2 Flashcards
How can we test what materials are conductors?
Testing rods of different materials as conductors.
Rosa need to be the same width and length. Each rod is coated with a thin outer layer of wax ‘’near one end
What materials are the best conductors?
• metals conduct energy better than non-metals
• copper is a better conductor than steel
• glass conducts better than wood
Energy transferred and thermal conductivity
The greater the thermal conductivity of a material, the more energy per second it transfers by conduction.
What makes good insulators?
• materials than have low thermal conductivity, so energy transfer through them is as low as possible
• necessary for warmth in the winter
• the thicker a layer of insulating material, the lower the rate of energy transfer through it
What is specific heat capacity?
• the energy needed to raise the temperature of 1 kg of the substance by 1 degree
What are the units of specific heat capacity?
• joule per kilogram degree Celsius (J/kg•C
Measuring specific heat capacity
• heat a block of known mass
• use a joulemeter to measure the energy supplied
• use a thermometer to measure its temperature rise
• insert measurements into the equation
Storage Heaters
• uses electricity at night (off peak)
• to heat special bricks or concrete blocks in the heater
• energy transfer from the bricks keeps the room warm
• bricks have a high specific heat capacity, so they store lots of energy
• warm up slowly when the heater element is on, and cool down slowly when it is off
Methods of reducing energy transfer at home?
• loft insulation
• cavity wall insulation
• thicker bricks with lower thermal conductivity
• double glazed windows
• aluminium foil between a radiator panel and the wall
Evaluate loft insulation
• loft insulation such as fibreglass reduces the rate of energy transfer through the roof.
• fibreglass is a good insulator
• the air between the fibres also helps to reduce the rate of energy transfer by conduction
• greater the number layers of insulation, thicker the insulation will be
• rate of energy transfer is less
Evaluate cavity wall insulation
• reduces the rate of energy transfer through the outer wall of the house
• cavity of an outer wall is the space between the two layers of brick that make up the wall
• insulation is pumped into the cavity
• it is a better insulator than the air it replaces
• traps the air in small pockets, reducing the rate of energy transfer by conduction.
Evaluate aluminium foil between a radiator panel and the wall
• reflects radiation away from the wall and so reduces the rate of energy transfer by radiation
Evaluate the use of double glazed windows
• two glass panes with dry air or a vacuum between the panes
• the thicker the glass is and the lower it’s rate of thermal conductivity, the slower the rate of energy transfer through it will be
• vaccum also prevents energy transfer by convection
External walls
• if the external walls of a warm building have thicker bricks and lower thermal conductivity, the rate of transfer of energy from the inside of the building to the outside will be lower and the cost of heating will be less
Solar panels
• heating with electricity or gas can be expensive
• absorb infrared radiation from the sun and generate electricity directly (solar cell panels) or heat water (solar heating panels)
• northern hemisphere - fitted facing south to absorb as much infrared radiation from the sun as possible
