DC Motors
If conditions for maximum power for a dc motor are established, the efficiency of the motor will be

100 %
60 to 70 %
Less than 50%
80 to 90 %

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DC Motors
In variable speed motor

A stronger commutating field is needed at low speed than at high speed
None of these
Same commutating field is needed at low speed than at high speed
A weaker commutating field is needed at low speed than at high speed

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