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D.C. Motors - section-1
  1. The condition for maximum efficiency for a D.C. generator is

    2. A.

     Eddy current losses = stray losses
    B.

     Hysteresis losses = eddy current losses
    C.

     Copper losses = 0
    D.

     Variable losses = constant losses

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  2. If a D.C. motor is connected across the A.C. supply it will

    3. A.

     Run at normal speed
    B.

     Not run
    C.

     Run at lower speed
    D.

     Burn due to heat produced in the field winding by eddy currents

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  3. The speed of a D.C. shunt motor can be increased by

    4. A.

     Increasing the resistance in armature circuit
    B.

     Increasing the resistance in field circuit
    C.

     Reducing the resistance in the field circuit
    D.

     Reducing the resistance in the armature circuit

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  4. The armature voltage control of D.C. motor provides

    5. A.

     Constant torque drive
    B.

     Constant voltage drive
    C.

     Constant current drive
    D.

     None of the above

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  5. Starters are used with D.C. motors because

    6. A.

     These motors have high starting torque
    B.

     These motors are not self-starting
    C.

     Back e.m.f. of these motors is zero initially
    D.

     To restrict armature current as there is no back e.m.f. while starting

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  6. If I2 be the armature current, then speed of a D.C. shunt motor is

    7. A.

     Independent of Ia
    B.

     Proportional to Ia
    C.

     Varies as Ia
    D.

     None of these

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  7. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because

    8. A.

     Back e.m.f. is equal to armature drop
    B.

     Armature drop is negligible
    C.

     Flux is proportional to armature current
    D.

     Flux is practically constant in D.C. shunt motors

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  8. A direct on line starter is used: for starting motors

    9. A.

     Up to 5 H.P.
    B.

     Up to 10 H.P.
    C.

     Up to 15 H.P.
    D.

     Up to 20 H.P.

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  9. The ratio of starting torque to full-load torque is least in case of

    10. A.

     Series motors
    B.

     Shunt motors
    C.

     Compound motors
    D.

     None of the above

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  10. For starting a D.C. motor a starter is required because

    11. A.

     It limits the speed of the motor
    B.

     It limits the starting current to a safe value
    C.

     It starts the motor
    D.

     None of the above

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