# Energy and Efficiency

PHYSICS UNIT 1: Energy and Efficency Mindmap

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• ENERGY AND EFFICIENCY
• Energy
• Can be transferred or stored or dissipated
• But cannot be created or destroyed
• Devices take in energy in one form and transfer it into another
• Only part of the energy is usefully transferred
• Remaining energy is wasted in surroundings
• E.g. most of a light bulb's energy is wasted as the bulb becomes hot
• Sankey diagram
• Shows relative proportions of energy transfer using arrows
• Efficiency
• Refers to proportion of energy that is usefully transferred
• If there is a large proportion of energy usefully transferred
• ...then the device is more efficient and cost-effective
• Pay-back time
• Replacing an old TV may cost £600
• But also provide an annual saving of £60
• Pay-back time = £600/£60 = 10 years
• Efficiency values are expressed as percentages or decimals
• Efficiency = (useful energy or power out / total energy or power in) x 100%
• Electrical energy
• Most energy transferred to houses and industry in this form
• Easily transferred...
• By heaters to heat surroundings
• Into light energy (lamp)
• Into sound energy (speakers)
• Into kinetic energy (electric fan)
• Amount transferred by appliance depends on...
• How long it is switched on
• How fast it transfers energy
• Refers to proportion of energy that is usefully transferred
• If there is a large proportion of energy usefully transferred
• ...then the device is more efficient and cost-effective