Physics - Energy efficiency 0.0 / 5 ? PhysicsEnergyGCSEAQA Created by: LunaShomeiRoseCreated on: 22-10-18 19:54 a light bulb has an efficiency of 0.3. what does this mean? 30% of the energy transferred in the light bulb is useful as it's transferred as light energy while the rest is wasted 1 of 8 what happens to the wasted energy? it disspotates into surroundings as thermal (heat) energy 2 of 8 How do you calculate energy efficiency? Useful energy output/ total energy input 3 of 8 if an object is 70% efficient, how much energy is wasted / transferred usefully? 70% is transferred usefully. 30% is wasted, dissipating into surroundings 4 of 8 A hob is heating water in pan. 15KJ of thermal energy is transferred by a hob. 12KJ passes into water. Calculate efficiency 12/15 =0.8 = 80% 5 of 8 How could you increase efficiency? Add lid so less energy is transferred 6 of 8 Electric current deliverers 60 watts to bulb. 3 watts are transferred as light. Calculate efficiency 3/60 = 0.05 = 5% 7 of 8 is it also true that efficiency = useful power output / total power input ? yes 8 of 8
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