# Energy and Efficiency

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- Created by: JessicaGrey
- Created on: 19-04-16 17:30

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- Energy and Efficiency
- Energy can be transferred BUT cannot be CREATED or DESTROYED
- When energy is transferred not all of it is useful, some many be given off as wasted energy.
- Wasted energy transfers to the surrounding

- When energy is transferred not all of it is useful, some many be given off as wasted energy.
- Sankey diagrams
- Width of arrow= amount of energy
- Arrow continuing straight= useful energy
- Arrows pointing down= wasted energy

- Pay back time
- eg. The double-glazing for a house costs £3,000 but saves £150 per year in fuel costs. What is its payback time?
- Answer; payback time = 3,000 ÷ 150 = 20 years

- Is something cost effective to install? How long will it take for me to start benefiting economically from it?

- eg. The double-glazing for a house costs £3,000 but saves £150 per year in fuel costs. What is its payback time?
- Efficiency
- Efficiency= useful energy out / total energy in x100%
- Efficiency= useful power out / total power in x100%
- Formulas given in exam

- Transfering electrical energy
- Everyday applianes
- Lamp; electrical energy-> heat and light energy
- Kettle; electrical energy-> heat and sound energy
- TV; electrical energy-> light, sound and heat energy
- The amount of energy an appliance transfers depends on how long the appliance is switched on and its power.

- E= P x t
- E is energy transferred in kilowatt-hours, kWh. P is power in kilowatts kW. t is time in hours, h
- E is energy transferred in joules, J. P is power in watts, W . t is time in seconds, s

- How much does it cost to use a washing machine for 1.5 hours? Power rating of washing machine = 2.0 kW cost of electricity = 6 pence per unit
- E=P x t so, E=2x1.5. E=3
- Units x cost per unit= total cost. So, 3 x 6p =18p

- E=P x t so, E=2x1.5. E=3

- Everyday applianes

- Energy can be transferred BUT cannot be CREATED or DESTROYED

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