Physics 1A - Energy: Efficiency of Machines & The Cost of Electricity 0.0 / 5 ? PhysicsEnergyGCSEAQA Created by: ex-JohnsonfamilyCreated on: 23-03-15 13:18 What is the formula for efficiency? Efficiency = Useful Energy Out / Total Energy In 1 of 6 How do you figure out efficiency if you don't know the energy in and out of the device? Efficiency = Useful Power Out / Total Power In 2 of 6 Can a device be 100% efficient? No device is 100% efficient and the wasted energy is usually spread out as heat. 3 of 6 What is the formula for energy transferred? Power x Time. 4 of 6 1 Kilowatt-Hour is... ...the amount of electrical energy used by a 1kW appliance left on for 1 hour. 5 of 6 What is the formula for cost of energy? Cost = Energy Transferred (kWh) x Price per kWh. 6 of 6
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