Electrical Machines
A 240 V DC series motor takes 40 A when giving its rated output at 1500 rpm. Its resistance is 0.3 ohms. The value of resistance which must be added to obtain rated torque at 1000 rpm is

 6 ohms.
 5.7 ohms.
 2.2 ohms.
 1.9 ohms.

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Electrical Machines
With the increase in speed of a DC motor

 both back emf as well as line current fall.
 both back emf as well as line current increase.
 back emf increases but line current falls.
 back emf falls and line current increases.

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