EE MCQ

SSC JE Electrical 2019 with solution SET-2
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For a three-phase induction motor slip at No Load ÷ slip at Full Load

In terms of slip, the actual speed of the motor (N) can be expressed as

N = Ns(1 − s)

At start, the motor is at rest and hence its speed N is zero.

s = 1 ( start)

This is the maximum value of slip s possible for the induction motor which occurs at start. While s = 0 gives us N = N. which is not possible for an induction motor. So slip of the induction motor cannot be zero under any circumstances.

Practically motor operates in the slip range of 0.01 to 0.05 i.e. 1 % to 5 %. The slip corresponding to the full load speed of the motor is called full load slip.

Related Question

SSC JE Electrical 2019 with solution SET-2
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Two coils are said to be ‘magnetically isolated’ provided the coefficient of coupling K

When there is no mutual flux between two coils, they are said to be magnetically isolated. In this case. k = 0 and M = 0.

SSC JE Electrical 2019 with solution SET-2
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Oxygen is a/an ____ gas?

Atoms or ions with unpaired electrons are attracted to a magnetic field; the more unpaired electrons, the greater is the attraction. Such substances are called **paramagnetic**. Molecular oxygen is a paramagnetic gas by virtue of its two unpaired electrons.

SSC JE Electrical 2019 with solution SET-2
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If the connected light load in a house is 3000W and power sub-circuit load 6000W, then what is the total number of sub-circuits required?

Indian Electricity Rules specify that the maximum load on a light/fan sub-circuit should not exceed 800 watts and the number of points should be limited to 10.

Hence for light load number of sub-circuit = 3000/800 = 3.75 = 4

Indian Electricity Rules specify that the maximum load on a power sub-circuit should not exceed 3000 watts and the number of outlets should be limited to two.

For the power sub-circuit load number of sub-circuit = 6000/3000 = 2

Total subcircuit = 4 + 2 = 6

SSC JE Electrical 2019 with solution SET-2
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Conductors experience skin effect in

**Skin Effect**

The steady direct current distributes itself uniformly over the whole section of a conductor but the alternating current does not distribute uniformly rather than it tends to concentrate near the surface of a conductor. In fact in the AC system, no current flows through the core and the entire current is concentric at the surface regions. This phenomenon is called skin effect.

The skin effect causes the effective resistance of the conductor to increase with the frequency of the current. The skin effect is due to eddy currents set up by the AC current. The skin effect has practical consequences in the design of radiofrequency and microwave circuits and to some extent in AC electrical power transmission and distribution systems.