EE MCQ

SSC JE Electrical 2019 with solution SET-2
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The number of brushes required for a 4 pole, lap wound DC machine is

**Lap Winding:-**In a lap winding the number of parallel paths (a) is always equal to the number of poles (p) and also to the number of brushes. In the given question number of poles is 4 hence the number of brushes will be 4.**Wave Winding:-** In wave windings, the number of parallel paths (a) is always two and there may be two or more brush positions.

Related Question

SSC JE Electrical 2019 with solution SET-2
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The work done on or by a unit N-pole in moving once around a closed path is equal to

**Ampere works law or Circuital Law**

This law relates to work done in a magnetic circuit i.e. closed magnetic flux path.

The work done on or by a unit N-pole in moving once round any complete path is equal to the product of current and number of turns enclosed by that path

SSC JE Electrical 2019 with solution SET-2
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Creeping is a term related to instruments?

**Creeping Error**

The slow but continuous rotation of the energy meter (Induction type) when only the pressure coil is excited and no current is flowing through the current coil is called creeping. This error may be due to excessive friction compensation, excessive voltage supply, stray magnetic field, etc.

In order to prevent creeping at no-load, two holes of the same radius are drilled in the disc on the opposite side of the spindle.

SSC JE Electrical 2019 with solution SET-2
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If a circular conductor carries a current of ‘I’ ampere having radius ‘r’ meter, then the magnetizing force at the center of the coil is given by

Magnetic Field Strength (H) gives the quantitative measure of strongness or weakness of the magnetic field.

H = B/μo

Where

B = Magnetic Flux Density

μo = Vacuum Permeability

The magnetic Field strength at the center of circular loop carrying current I is given by

B = μoI/2r

B/μo = I/2r

H = I/2r At/m

Where r = Radius

SSC JE Electrical 2019 with solution SET-2
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The conductor tied between two supports takes the shape of a ‘catenary’ due to ____?

The difference in level between points of supports and the lowest point on the conductor is called sag.

When the conductor is suspended between two supports at some level, it takes the shape of a catenary. However, if the sag is very small compared with the span, then the sag-span curve is like a parabola.

The tension at any point on the conductor acts tangentially. Thus tension To at the lowest point O acts horizontally.