DC Motors
The variable resistor shunting the field of a dc series motor is called a

Potential divider
Field divertor
Armature divertor
Voltage regulator

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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

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

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