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Motional EMF in an Open Conductor

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Question

An electric motor operates with an efficiency of $90$ %. A pump operated by the motor has an efficiency of $80$ %. The overall efficiency of the system is:

A

85 %

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B

100 %

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C

72 %

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D

60 %

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Solution

The correct option is D $72 %$
Efficiency $=$ (Efficiency of motor) $\times$ (Efficiency of pump)
Efficiency $= 0.9 \times 0.8 \times 100$ % $= 72$ %

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