P1 Revision Notes
- Energy is transferred and stored
- They are not different "forms".
- All objects emit infrared radiation
- The bigger the difference between the object and it's surroundings, the faster energy is transferred.
- Measured with a thermopile
- The Leslie Cube: Black surfaces give out more infrared radiation than white surfaces, dull surfaces give out more infrared radiation than shiny surfaces.
- Kinetic theory describes the energy of particles and the way they move.
Conduction and Convection
- Conduction is how energy is transferred through solids when heated.
- Conductors transfer energy easily
- Insulators do not transfer energy easily
- Convection is how energy is transferred in liquids and gases.
Evaporation and Condensation
- Evaporation is a liquid gaining enough heat energy for particles to escape and for the liquid to change state to a gas
- Condensation is when a gas loses heat energy and it cools and changes state to a liquid.
- An example of evaporation and condensation is the water cycle
Rate of Energy Transfer
- An object transfers energy to its surroundings depending on the material it's made from, it's size and shape (large surface area transfers energy faster), the type of surface and the temperature difference between the object and it's surroundings.
- U-value shows how well something acts as a thermal insulator, the lower number the better.
- Insulation saves money on heating bills.
- Payback time is the amount of time it takes to save as much money as the insulation cost.
Specific Heat Capacity
- Specific heat capacity is how much energy is needed to raise the temperature of 1kg of material by 1 degree celcius.
- Specific heat capacity is measured in joules per degree celcius.
- E = m x c x θ
Energy transferred = mass (kg) x specific heat capacity x temperature change
Energy transfer and waste
- Sankey diagrams show energy transfer and waste.
- An efficient object does what it is designed for using as little energy as possible and wasting as little as possible.
- Efficiency = useful energy out ÷ total energy in
- Batteries store energy in chemicals. The energy is transferred by an electrical current when the battery is connected to a circuit
Energy and Appliances
- Energy is transferred from a power station to places as an electrical current.
- Free electrons in the metals the cables are made of, transfer charge down the line. The rate at which this happens is measured in amperes (A).
- Watts are joules per second.
- J = w x t
The Cost of Electricity
- Electricity companies charge for how many kilo-watt hours are used.
- kWh = kW x h
- total cost = kwh x cost…