DC MACHINES

1. The developed electromagnetic force and/or torque in electro mechanical energy conversion system act in a direction that tends
a) to increase the stored energy at constant flux
b) to decrease the stored energy at constant flux
c) to decrease the coenergy at constant mmf.
d) to decrease the stored energy at constant mmf
ans: b

2. For a linear electromagnetic circuit, the following statement is true
a) Field energy is equal to the coenergy
b) Field energy is greater than the coenergy
c) Field energy is lesser than the coenergy
d) Coenergy is zero
ans: a

3. In an electromechanical energy conversion device, the developed torque depends upon
a) stator field strength and torque angle
b) stator field and rotor field strengths
c) stator field and rotor field strengths and torque angle
d) stator field only
ans: c

4. In electro mechanical energy conversion devices , a small air gap is left between the stator and rotor in order to
a)  reduce the reluctance of the magnetic path
b) increase flux density in the air gap
c) permit mechanical clearance
d) none of the above
ans: c

5. A rotating electrical machine having its self inductance of both stator and rotor winding's, independent of rotor position will definitely not develop
a) starting torque
b) synchronizing torque
c) hysteresis torque
d) reluctance torque
ans: b

6. A circular metallic disc is placed in a vertical magnetic field of constant induction in the downward direction. If the disc is rotated in a horizontal plane , the emf induced will be
a) zero
b) constant independent of disc size
c) increasing radically in the outward direction
d) decreasing radically in the outward direction
ans: a

7. The emf induced in a conductor rotating in a bipolar field is
a) dc
b) ac
c) dc and ac both
d) none of these
ans: b