Permanent Magnet & Brushless D.C Motor - MCQs with Answers

Permanent Magnet & Brushless D.C Motor - MCQs with Answers

Q1. The torque constant (K_m), of a permanent magnet d.c. motor is 0.25 V sec/radian and armature resistance is 2 ohm. If the applied armature voltage is 90 V, then its zero speed torque is

a. 10.45 N-m
b. 11.25 N-m
c. 13.65 N-m
d. 15.56 N-m

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Q2. The speed of permanent magnet d.c. motor cannot be controlled by

a. Flux control method
b. Rheostatic control method
c. Electronic circuits
d. None of these

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Q3. The number of windings on the field of permanent magnet d.c. motor is

a. More compared to shunt motor
b. Less compared to shunt motor
c. Absent
d. None of these

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Q4. Permanent magnet d.c. motors are extensively used in

a. Automobiles
b. Heaters
c. Air conditioners
d. All of these

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Q5. In the biomedical instruments like artificial heart pumps, the commonly used motor is

a. Permanent magnet d.c. motor
b. Brushless d.c. motor
c. Ward-Leonard system
d. Series motor

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Q6. A machine operating as motor may go into regenerative braking mode if its speed becomes

a. Sufficiently high to make back emf greater than supply voltage
b. Sufficiently low to make back emf greater than supply voltage
c. Sufficiently high to make back emf half of the supply voltage
d. Sufficiently low to make back emf half of the supply voltage

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