Efficiency - Power useful energy = efficiency x total energy efficiency = useful energy total energy total energy = useful energy efficiency (Power is energy per second, the equations are the same but energy is replaced by power) 1. A 60W television transfers 30W to light and sound. What is the efficiency of the television? 2. A radio transfers 20W. The radio turns 5W into sound is. What is the efficiency of the radio? 3. A computer transfers 120W. 80W of heat is given out. What is the efficiency of the computer? How much is wasted? 4. An electric fire has a power rating of 2 kW. 200 W is wasted. What is the efficiency of the electric fire? 5. A kettle is rated at 1.2 kW. 1.1 kW is transferred to the water. Calculate the efficiency of the kettle. 6. A tungsten filament light bulb of 100W is only 1% efficient. How much power is wasted and how much is useful? 7. A compact fluorescent lamp (CFL) which is equivalent to the 100W tungsten is rated at 20W. It is 20% efficient. How much is power is wasted and how much is turned into light? How efficient is it compared to the tungsten filament bulb? 8. A LED bulb equivalent to the 100W tungsten is 7W. How much more efficient is it? 9. Official figures comparing bulbs for the same amount of light per Watt are; Tungsten 14, CFL 55 and LED 123. How do the efficiencies compare? 10. A 40W electric fan is 60% efficient. How much power is wasted as heat and sound? And finally 11. A wind farm over a year could have produced 17,586,000 MW hours of energy running at full capacity. In reality, 3,881,900 MW hours was generated so what was the efficiency?
