The total energy supplied to an electric motor is E. Energy Q is wasted and the remaining energy does useful work.
What is the efficiency of the motor?
A Q/E
B (Q/E) - 1
C 1 - (Q/E)
D (1 - Q) / E
ANSWER: C
The Physics Behind
- Efficiency is the useful work or energy divided by the input energy or the total energy supplied.
- Let E be the total energy and W be the remaining energy or work.
E = W + Q
- With efficiency as e, the above can then be written mathematically as
e = W / (W + Q)
e = (E - Q) / (W + Q)
e = E/(W + Q) - Q/(W + Q)
but E = W + Q
so, e = E/E - Q/E
e = 1 - Q/E
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