EE MCQ

SSC JE Electrical 2019 with solution SET-1
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The voltmeter is shown in the circuit reads:

Total resistance in the given circuit

R = (250 + 250)MΩ = 500 MΩ

Current I = V/R = 24/(500 × 103)

Now the Voltage in the voltmeter

= \dfrac{{24}}{{500 \times {{10}^3}}} \times 250 \times {10^3}

V = 12 V

Related Question

SSC JE Electrical 2019 with solution SET-1
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The law that explains about the economic size of a conductor is:

In transmission lines, a large amount of power is transmitted over a long distance. So, voltage regulation is not important because in some lines, 40% regulation is considered satisfactory. In such cases, only the economy is important. The cost of the conductor is the main part which decides the total cost of the transmission line. Hence, the selection of the proper size of the conductor for a particular line is most important.

The most economical area of the conductor is that for which the total annual cost of the transmission line is minimum. This is known as Kelvin’s law and was given by Lord Kelvin in the year 1881.

It states that the most economical cross-section of a conductor is the value at which the annual cost of the electric energy wasted in the conductor, and annual cost of the interest and depreciation on the capital cost of the conductor are equal. Thus, the total annual charge on an overhead transmission line can be expressed as :

Total annual charge =P1 + P2α or Variable part of the energy charge = Annual cost of energy wasted.

where

P1 and P2 are constants

α is the area of the X-section of the conductor.

SSC JE Electrical 2019 with solution SET-1
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A shaded pole motor is basically a motor

The shaded-pole motor is the original type of AC single-phase induction motor. Shaded pole-type single-phase induction motors are provided with shading rings on their poles which are the projected type of poles. The stator of such motors has projected poles like DC machines as shown in Fig. 5.7. The rotor is a squirrel cage type similar to that of split-phase-type motors. The poles are excited by giving a single-phase AC supply. A single-turn thick coil in the form of a ring called the shading ring is fitted on each side of every pole as shown. The portion of the poles where the shading ring is fitted is called the shaded portion, while the other portion is called the unshaded portion.

The shaded pole motor has the lowest starting torque as compared to the all single-phase induction motors.

SSC JE Electrical 2019 with solution SET-1
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P = ρQHg is the water power equation. Head ‘H’ is measured in meter ‘g’ gravity constant is measured in meter/second square, then the measuring unit of ‘Q’, the flow rate of water is:

P = ρ QHg is the water power equation.

Where

H = heead = meter

g = gravity =m/s2

ρ =density = (kg/m3)

P = power = watt = N-m/sec

Q = water flow rate = m3/sec

SSC JE Electrical 2019 with solution SET-1
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A three-phase induction machine, when it is operating like a motor, the range of slip is given by

Torque speed characteristic of induction motor

Motoring mode: 0 ≤ s ≤ 1

For this range of slip, the load resistance in the circuit is positive, i.e. torque developed is in the direction in which the rotor rotates.

In this region the value of slip lies between 0 to 11 i.e., slip is positive.

The motor rotates in the same direction as that of a rotating magnetic field.

At s = 0 (synchronous speed), the torque produced by the motor is zero because the induced voltage in the rotor is zero when N= Ns.

The torque increases as the slip increases while the air gap flux remains constant.

The torque-slip characteristic from no-load to somewhat beyond full-load is almost linear.

Generating mode: s <0

In this operating mode, the slip s is negative i.e., s < 0. The slip will be negative if and only if the rotor speed N is greater than the synchronous speed Ns (N> Ns). However, the rotor and R.M.F both rotate in the same direction.

In this region, the motor acts as a generator and return the power back to a.c. source.

Braking or plugging Mode: s > 1

In this region, the value of slip is greater than 1 and the rotor rotates in the opposite direction of the rotating magnetic field.

This is achieved by interchanging any two phases of the stator supply.

SSC JE Electrical 2019 with solution SET-1
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Relate ‘Reluctance with the following:

The reluctance of any part of a magnetic circuit may be defined as the ratio of the drop in magnetomotive force to the flux produced in that part of the circuit. It is measured in ampere-turns/Weber and is denoted by S.

Reluctance = m.m.f ⁄ flux