EE MCQ

SSC JE Electrical 2019 with solution SET-1
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A coil is wound with 50 turns and a current 8A produces a flux of 200μWb. Calculate the inductance of the coil

The inductance of the coil is given by the relation

L = Nφ/I

Where

N = number of turns = 50

φ = flux = 200μWb

I = current = 8 A

L = 50 × 200 × 10−6 ⁄ 8

L = 1.25 mH

Related Question

SSC JE Electrical 2019 with solution SET-1
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Which of the following should be used under no-load conditions?

Isolator or disconnecting Switch: An isolator is a switch that is designed to open a circuit under no-load condition. Its main purpose is to isolate one portion of the circuit from the other and is not allowed to be opened while current is flowing in the line. Such switches are used on both sides of a circuit breaker so that its repair works or replacement could be done.

Note that an isolator is never opened until the circuit breaker in the circuit is opened and it is closed before the circuit breaker is closed. If an isolator is switched OFF when a high current is flowing through the circuit, a heavy spark will be produced. This heavy spark may break the supporting insulator of the isolator which may cause a fatal accident to the operator.

SSC JE Electrical 2019 with solution SET-1
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Two coupled coils with L1 = L2 = 0.5H have a coupling coefficient of K = 0.75. The turn ratio N1 ⁄ N2 = ?

The self-inductance is given as

L = μN2A/I

L ∝ N2

where

N is the number of turns of the solenoid

A is the area of each turn of the coil

l is the length of the solenoid

and μ is the permeability constant

L1/L2 = N21/N22

0.5/0.5 = N21/N22

N1/N2 = 1

SSC JE Electrical 2019 with solution SET-1
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What is the reason behind using a centrifugal switch in a single-phase induction motor?

The centrifugal switch is used to disconnect the starting winding of the motor once the motor approaches its normal operating speed i.e 50% – 70% speed.

SSC JE Electrical 2019 with solution SET-1
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An electric motor in which both the rotor and stator fields rotate with the same speed is called

In the synchronous motor, the stator and rotor rotate at the same speed.

SSC JE Electrical 2019 with solution SET-1
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_______ is the measuring unit of inductive susceptance

Susceptance is symbolized by the capital letter B. It is the reciprocal of AC reactance. Susceptance, like reactance, can be either capacitive or inductive. In the case of a magnetic field, the susceptance is inductive. In the case of an electric field, the susceptance is capacitive. Capacitive susceptance is symbolized BC and inductive susceptance is symbolized BL. In the case of a magnetic field, the susceptance is inductive. In the case of an electric field, the susceptance is capacitive. Inductive susceptance is assigned negative imaginary number values, and capacitive susceptance is assigned positive imaginary number values.

The formula for inductive susceptance is

BL =–1/2πfL

The unit of Inductive susceptance is Siemen or Mho.