DC Motors
If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor

Of higher H.P. should be selected
Is to be de-rated by a factor recommended by manufacturer and select the next higher H.P. motor
Of lower H.P. should be selected
Can be used for 50°C ambient temperature also

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DC Motors
In a dc compound machine,

Both play equally dominant role
Either can play dominant role
Shunt field winding plays dominant role
Series field winding plays dominant role

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DC Motors
In variable speed motor

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