AS Physics Energy

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  • Created by: ellie
  • Created on: 01-06-13 14:27
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  • Energy
    • Potential
      • Kinetic Energy= 1/2mv^2
      • Work done to raise an object= force * distance moved in that direction (=mgdeltah). This is its change in gravitational potential energy
      • After object falls through a vertical height of deltah,1/2mv^2 is equal to mgdeltah
      • Apendulum bob- Kinetic energy = mg(h-h
      • Fairground downward track- work done to overcome friction and air resistance= mgh- 1/2mv^2
    • Power
      • Power is defined as the rate of transfer of energy
      • Power= change in work done/ change in time
      • Electrical
        • The power of a bulb can be measured in a circuit with a joulemeter. The difference in readings before and after the bulb is turned on is the energy supplied to the bulb. Power can be found using this value and the time
      • Engine
        • Output power of engine can be called its motive power
        • At constant height and velocity, the motive force= any resistant forces
        • Work done per second= force * distance moved per second
        • Output power of engine= P=Fv
      • Muscle
        • Your gain of potential energy= your weight gain * total height gain
        • Your muscle power= weight * height gain/ time taken
    • Renewable
      • Solar
        • A solar cell panel produces electricity directly
        • A Solar heating panel can heat water to 70 degrees and can absorb up to 500 J/s of energy on a British Summer day.
      • Wind
        • Typical modern wind turbine can generate about 2MW of electrical power
        • Kinetic energy per second of wind passing through turbine= 1/2pv^3A, where p= denisty of air, v= speed of air and A= area the blades sweep
      • Water
        • hydroelectric and tidal power stations make use of potential energy released by water when it runs to a lower level
        • Hydroelectric power stations release less water per second but from a much higher height than tidal power stations.
    • Efficiency
      • Work done= Fs= W
      • Output Pwer= Fv where F= output force and v= speed of object
      • Efficiency of machine= work done by machine/ energy supplied to machine
      • Efficiency= output power of machine/ input power of machine
      • To find percentage efficiency times by 100
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