Energy revision

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  • Created on: 15-05-14 18:29
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Energy transfer
Efficiency (%) = (useful energy output ÷ total energy input) x 100
(Change in) Gravitational potential energy (J) = mass (kg) x g x height (m)
Work done (J aka. Nm) = power (W) x time (s)
Work done (J) = force (N) x distance (m)
Kinetic energy (J) = ½ x mass (kg) x speed2 (m/s)
m = <3
Density (kg/cm3) = mass (kg) ÷ volume (cm3) (N.B. V )
- When energy converted, some into unwanted forms = wasted energy
- More wasted energy less efficient appliance
Sankey diagram
Energy saving bulb
for a filament bulb
- Energy is ability to do work
- Power is rate of doing work
- 1J of work is done when 1N is applied through 1m in the direction of the force
- Work done = energy transferred
- The Law of Conservation of Energy: `Energy is not created or destroyed in any
process' (only ever converted)
- Amount of energy in universe is constant but Earth is small and some escapes
through atmosphere
- N.B. Energy is transformed from one type to another but transferred between
objects
Thermal energy
- Heat always moves from hot to cold
- Metals are good conductors as they have free electrons
- Convection: when heat energy is carried by hot particles rising and cold particles
falling. Happens in gases and liquids. Hot air rises because more space between
the particles as they are moving fast, so less dense. Cold particles fall for
opposite reasons.

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Energy transfer
- Conduction: when heat energy is transferred from particles to neighbouring
particles. Happens in solids.
- Radiation (aka. Infrared): electromagnetic waves so does not need particles (and
can happen in a vacuum). Affected by colour of the surfaces.…read more

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Energy transfer
Power type Advantages Disadvantages Renewable
Nuclear- an isotope of - Clean- doesnt emit - Risk of accidents No
uranium (The fuel) used to greenhouse gases - Problem of disposal of
boil water steam turns - Low cost per unit of radioactive material once power
turbine turns generator electricity station finished with it
Hydroelectric- dam built to - Low cost as no fuel - Loss of land ruins habitats Yes
trap water (GPE) water cost - Drought/climate change affect it
allowed to flow through…read more

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