# Test: Magnetic Circuits of Electrical Machines

## 10 Questions MCQ Test Topicwise Question Bank for Electrical Engineering | Test: Magnetic Circuits of Electrical Machines

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Attempt Test: Magnetic Circuits of Electrical Machines | 10 questions in 30 minutes | Mock test for Electrical Engineering (EE) preparation | Free important questions MCQ to study Topicwise Question Bank for Electrical Engineering for Electrical Engineering (EE) Exam | Download free PDF with solutions
QUESTION: 1

### What is the inductance of a coil in which a current of 0.1A increasing at the rate of 0.5 A/s represents a power flow of 0.5 watt?

Solution:

Power flow through the coil is: p = ei or, QUESTION: 2

### A coil of 100 turns is wound on a torroidal magnetic core having a reluctance of 104 AT/Wb. When the coil current is 5 A and is increasing at the rate of 200 A/s, the voltage across the coil would be (assume coil resistance to be 2 Ω)

Solution:    QUESTION: 3

### The field winding of a dc electro-magnet is wound with 960 turns and has a resistance of 50 Ω. The excitation voltage is 230 V and the magnetic flux linking the coil is 5 mWb. The energy stored in the magnetic field is

Solution:

Current through the field winding,   So, energy stored in magnetic field QUESTION: 4

The flux in a magnetic core is alternating sinusoidally at a frequency of 600 Hz. The maximum flux density is 2 Tesla and the eddy current loss is 15 Watts. What would be the eddy current loss in the core if the frequency is raised to 800 Hz and the maximum flux density is reduced to 1.5 Tesla?

Solution:

We know that eddy current loss, or  QUESTION: 5

Two inductances of 15 mH and 25 mH are connected in series such that their fluxes oppose each other. They are so placed that the coefficient of coupling is 0.8. The value of mutual inductance between them will be

Solution: QUESTION: 6

The property of a material which opposes the production of magnetic flux in it is known as:

Solution:

Resistance in electrical circuit corresponds to reluctance in magnetic circuit. Reluctance opposes the production of magnetic flux in a magnetic circuit and resistance opposes the flow of current in electrical circuit.

QUESTION: 7

Air exhibits

Solution:
QUESTION: 8

The laws of electromagnetic induction are summarized in the following equation:

Solution:

From Faraday’s law of electromagnetic induction, (minus sign is due to Lenz’s law).

QUESTION: 9

EMF induced in a coil rotating in a uniform magnetic field will be maximum when the

Solution: Hence, emf induced is maximum when di/dt is maximum.

QUESTION: 10

The emf induced in a conductor rotating in a bipolar field is

Solution:

It is nothing but the EMF in a conductor in a rotating magnetic field is sinusoidal and alternating. It may be observed from the process of EMF generation in a conductor. In the initial position, the conductor is parallel with magnetic flux lines. So, there is no EMF. When it reaches perpendicular to flux lines, EMF generation is maximum. After that again it reaches the parallel path to flux lines. So, EMF is zero now. This same action happens again, but it is in the reverse direction. So, again there is an EMF but is in the negative direction. Hence, we get the sinusoidal waveform that has a bipolar field and that is nothing but the AC. Use Code STAYHOME200 and get INR 200 additional OFF Use Coupon Code