State the equation linking useful energy transfer output, total input energy transfer, and efficiency.
60 J of energy is transferred from a cell to a lamp.
16 J is transferred from the lamp to the thermal store of the surroundings.
State the amount of energy that is usefully transferred.
Calculate the efficiency of the lamp.
A student measures the energy transferred to a motor and the energy output by the motor.
The student says to the class that the motor has an efficiency of 1.5. Another student politely explains that this can't be correct.
Explain how the second student knows the first student's answer is incorrect.
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