Key points over the whole topic. Forms of energy
- Energy exists in different forms.
- Energy can change into one form into another form.
- When an object falls and gains speed, its gravitational potential energy decreases and its kinetic energy increases.
Conservation of energy
- Energy cannot be created or destroyed.
- Conservation of energy applies to all energy changes
- Useful energy is energy in the place we want it and in the form that we need it.
- Wasted energy is energy that is not useful energy.
- Useful energy and wasted energyboth end up being transferred to the surroundings, which becomes warmer.
- As energy spreads out, it gets more and more difficult to use for further energy transfers.
Energy and efficiency
- The efficiency of a device = useful energy transferred by the device ÷ total energy aupplied to the device (x100%)
- No machine can be more than 100% efficient.
- Measures to make machines more efficient include reducing friction, air resistance, electrical resistance and noise due to vibrations.
- Electrical appliances can transfer electrical energy into useful energy at the flick of a switch.
- Uses of everyday electrical appliances including heating, lighting, making objects move (using an electric motor) and creating sound and visual images.
- An electrical appliance is designed for a particular purpose and should waste as little energy as possible.
- Power is rate of transfer of energy.
- You can calculate power using P=E/T
- Efficiency = useful power out/total power in (x100%)
Using electrical energy
- The kilowatt-hour is the…