Quiz on dc Machine

Torque in a DC series motor is

• Proportional to armature current

• Proportional to square of armature current

• Proportional to field current

• Proportional to back emf

The shaft torque of a 10kW DC motor at a speed of 600 rpm is

• 6.28 N.m

• 62.8 N.m

• 628 N.m

• 0.628 N.m

The angular velocity of a motor shaft which rotates at 1200 rpm is;

• 1256 rad/s

• 12.5 m/s

• 125. 6 N.m

• 125.6 rad/s

The back emf generated in a dc lap wound motor with following specification. Armature current - 10ANo. of poles - 4No. of armature conductor - 100Rated speed - 1200 rpm Flux per pole- 1 Wb

• 110 V

• 220 V

• 1kV

• 2000 V

Which of the following losses are significantly reduced by laminating the core of a D.C. generator?

• Hysteresis losses

• Eddy current losses

• Windage losses

• Copper losses

WHEN THE ARMATURE OF A D.C. MOTOR ROTATES, E.M.F. INDUCED IS

• Counter emf

• Self induced emf

• Mutually induced emf

• Self and mutually induced emf

THE POWER MENTIONED ON THE NAME PLATE OF AN ELECTRIC MOTOR INDICATES

• Gross power

• Power developed in the armature

• Shaft power

• Power input

IN THE D.C. MOTOR THE IRON LOSSES OCCUR IN

• Field coil

• In the armature coil

• In the armature core

• In the Yoke

IN A D.C. SERIES MOTOR, IF THE ARMATURE CURRENT IS REDUCED BY 50%, THE TORQUE OF THE MOTOR WILL BE EQUAL TO

• 100% OF THE PREVIOUS VALUE

• 50% of the previous value

• 25% of the previous value

• 60% of the previous value

What happens when the DC motor speed increases?_

• Back EMF decreases, but line current increases

• Back EMF increases, but line current decreases

• Both the back EMF and the line current decrease

• Both the back EMF and the line current increase