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What is the effiency of a motor that converts100j of electrical energy into 70j of useful kinetic energy?
70 percent
What is the efficiency of a motor that converts 100J of electric energy into 70j of useful energy?
70% efficient Take: Useful work out --------------------- X 100 = efficiency Work in
Is heat energy produced with the light energy in a torch?
Yes. The heat and light energy in a torch are separate. From the total energy input to the torch (chemical energy from batteries), Some is useful (the light energy) and some is wasted. (heat/thermal energy) The more efficient an appliance is ,the less energy out of the input energy is wasted. For example, an appliance may be 70% efficient. If it is supplied with 100J (joules) of energy, 70J will be useful and 30J will be wasted. Along with light energy, heat energy is also produced by a torch and is wasted. Heat energy is the most common form of wasted energy in appliances. Other appliances will waste energy in the form of heat, though it may not always be obvious.
