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Test: Torque in DC Machines - Electrical Engineering (EE) MCQ


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10 Questions MCQ Test Electrical Machines - Test: Torque in DC Machines

Test: Torque in DC Machines for Electrical Engineering (EE) 2024 is part of Electrical Machines preparation. The Test: Torque in DC Machines questions and answers have been prepared according to the Electrical Engineering (EE) exam syllabus.The Test: Torque in DC Machines MCQs are made for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Torque in DC Machines below.
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Test: Torque in DC Machines - Question 1

 What is the principle of torque production in a dc machine?

Detailed Solution for Test: Torque in DC Machines - Question 1

Though all the mentioned laws contribute towards the torque generation, but primarily its the Lorentz’s forces which initiate and define the torque direction.

Test: Torque in DC Machines - Question 2

 The torque induced beyond the pole shoes in the DC machine is

Detailed Solution for Test: Torque in DC Machines - Question 2

The magnetic field vanishes at the pole terminals and thus the cross product with the magnetic field yields zero.

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Test: Torque in DC Machines - Question 3

The simple rotating loop between pole faces connected to a battery and resistor through a switch, the specifications of this machine are radius = 0.5m, length 1m, resistance = 0.3 ohms and magnitude strength = 0.25T is supplied with 120V. Suddenly the switch is closed at t=0, what is observed in the circuit?

Detailed Solution for Test: Torque in DC Machines - Question 3

 Initially the induced emf in the armature is zero. But the current will flow as there is terminal source voltage.

Test: Torque in DC Machines - Question 4

The simple rotating loop between pole faces connected to a battery and resistor through a switch, the specifications of this machine are radius = 0.5m, length 1m, resistance = 0.3 ohms and magnitude strength = 0.25T is supplied with 120V. What will be the magnitude of the following current at t=0+?

Detailed Solution for Test: Torque in DC Machines - Question 4

 I=(V-E)/r
=(120-0)/0.3
=400 A.

Test: Torque in DC Machines - Question 5

If the torque induced is zero in the dc machine, it can be said that

Detailed Solution for Test: Torque in DC Machines - Question 5

The torque at steady state of operation is zero as the emf induced is equal to the source voltage. Also the the very much starting the current will be zero which will not let the emf to get induced.

Test: Torque in DC Machines - Question 6

The simple rotating loop between pole faces connected to a battery and resistor through a switch, the specifications of this machine are radius = 0.5m, length 1m, resistance = 0.3 ohms and magnitude strength = 0.25T is supplied with 120V. What is the steady state angular velocity at no-load?

Detailed Solution for Test: Torque in DC Machines - Question 6

 v = V/(2*r*l*B)
= 120/(2*0.0005*1*0.25)
= 480 rad/s.

Test: Torque in DC Machines - Question 7

 If the torque is in the direction of rotation, the DC machine acts as

Detailed Solution for Test: Torque in DC Machines - Question 7

The electromagnetic torque generated in the dc generator is in the direction in which the prime mover is rotated.It is produced due to the action of armature current and stator field.

Test: Torque in DC Machines - Question 8

The cogging torque is absent in the permanent magnet dc machine is due to

Detailed Solution for Test: Torque in DC Machines - Question 8

 It is due to the fact that no field poles are induced in PMDC to create magnetic flux leading to harmonics.

Test: Torque in DC Machines - Question 9

DC Motor torque depends on

Detailed Solution for Test: Torque in DC Machines - Question 9

The torque will indeed depend on the geometry as well the magnetic materials used in the construction of the dc machine. Though this remains constant with the machine.

Test: Torque in DC Machines - Question 10

For a universal motor, the rated supply current is 10A giving a rated torque of 100 N-m. If a current of 5A is applied, what will be generated torque vary to?

Detailed Solution for Test: Torque in DC Machines - Question 10

The torque is proportional to the square of the current.
So the new torque will be 100*(2^2)= 400 N-m.

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