When the motor is at its maximum speed then back emf will be______________?

Related Mcqs:

1. An aeroplane of wingspan 10m flies from the equator towards the North Pole. The wings are perpendicular to the vertical component of the earths magnetic field (B = 4×10-5T). At maximum speed an emf of 96mV is induced across the wing tips. The maximum speed of the aeroplane is____________?

   A. 150msec-1
   B. 384msec-1
   C. 38.4msec-1
   D. 200msec-1

2. A metal rod of 25 cm length is moving at a speed of 0.5/sec in direction perpendicular to 0.25T magnetic field. Emf produced in the rod is_____________?

   A. 0 volt
   B. 3.125 volt
   C. 31.25 volt
   D. 0.03125 volt

3. ________________ motor is a constant speed motor?

   A. Synchronous motor
   B. Schrage motor
   C. Induction motor
   D. Universal motor

4. A coil of wire is arranged with its plane perpendicular to a uniform magnetic field o flux density B. when the radius of the coil increases from r1 to r2 in time Δt then what is the emf induced in the coil ?

   A. ωB/r22-r12/Δt
   B. ωB(r2-r1)2/Δt
   C. ωB(r22-r12)/Δt
   D. ωB(r22+r12)/Δt

5. emf induced in a circuit according to Faradays law depends on the_____________?

   A. maximum magnetic flux
   B. rate of change of magnetic flux
   C. change in magnetic flux
   D. initial magnetic flux

6. The emf induced in a coil by a changing magnetic flux may have unit as______________?

   A. ms-1A
   B. ms-2A-1
   C. kgms2A-1
   D. kgm2s-1A-1

7. The emf induced in a conductor of unit length moving with unit velocity at right angles to a magnetic field is equal to_____________?

   A. Magnetic flux density
   B. Torque
   C. Mutual induction
   D. Motional emf

8. A wound rotor induction motor is preferred, as compared to squirrel cage induction motor, when major consideration is____________________?

   A. slop speed operation
   B. high starting torque
   C. low windage losses
   D. all of the above

9. Two coils have inductances of 8 mH and 18 mH and a co-efficient of coupling of 0.5. If the two coils are connected in series aiding, the total inductance will be______________?

   A. 32 mH
   B. 38 mH
   C. 40 mH
   D. 48 mH

10. Two oppositely charged balls A and B attract third conducting ball C when placed near them turn by turn. Then ball C must be______________?

    A. positively charged
    B. electrically neutral
    C. negatively charged
    D. positively and negatively charged