SSC JE Basic Electrical Questions (2009 – 2018) Solved (Part-3)

Ques.91. The permissible variation of frequency in power system P_{s} is (SSC – 2009)

± 1%

± 3%

± 5%

± 10%

Answer.2. ± 3%

Explanation

According to CENTRAL ELECTRICITY REGULATORY COMMISSION OF INDIA

Ideal Range of frequency variation

f = 50 ± 1%

49.5 to 50.5 Hz

Practical permissible Range of frequency variation

f = 50 ± 3%

48.5 to 51.5 Hz

The grid frequency should be maintained at 48.6 Hz. and above at all times.

Ques.92. In a series R-L-C circuit, susceptance is equal to (SSC – 2009)

1/X

1/R

R/Z^{2}

X/Z^{2}

Answer.4. X/Z^{2}

Explanation:-

In electrical engineering, susceptance (B) is the imaginary part of admittance, where the real part is conductance. The inverse of admittance is impedance, where the imaginary part is reactance and the real part is resistance.

The general equation defining admittance is given by

where

Y is the admittance, measured in Siemens.

G is the conductance, measured in Siemens.

j is the imaginary unit and

B is the susceptance, measured in Siemens.

The admittance (Y) is the inverse of the impedance (Z)

Ques.93. The current read by the ammeter A in the AC circuit shown in the following figure is (SSC – 2009)

9A

5 A

3 A

1 A

Answer.2. 5 A

Explanation:-

Current for a Parallel RLC Circuit

I_{s} = 5A

Ques.94. The voltage across the various elements are marked, as shown in the figure given below. The maximum input voltage is (SSC – 2009)

27 V

24 V

10 V

5 V

Answer.4. 5 V

Explanation

Maximum Input voltage in series RLC circuit

Ques.95. The principle of dynamically induced emf is utilized in (SSC – 2009)

Choke

Transformer

Thermocouple

Generator

Answer.4. Generator

Explanation:-

In dynamically induced emf the magnetic field system is kept stationary, and the conductor is moving, or the magnetic field system is moving, and the conductor is stationary thus by following either of the two processes the conductor cuts across the magnetic field and the emf is induced in the coil. Hence the emf induced in a coil due to the relative motion of the conductor and the magnetic field is called dynamically induced emf.

Dc generator works on the principle of dynamically induced emf. Whenever a conductor cuts magnetic flux, dynamically induced e.m.f. is produced in it according to Faraday’s Laws of Electromagnetic Induction. This e.m.f. causes a current to flow if the conductor circuit is closed

Ques.96. The rating of fuse is expressed in terms of (SSC – 2009)

Amperes

Volts

VAR

KVA

Answer.1. Amperes

Explanation:-

Fuses are ‘overcurrent protection devices’ and therefore will be rated in current units, i.e. Amperes. A fuse opens or “blows” and opens the circuit when the current (amperes) exceeds a preset limit.

Ques.97. When the frequency of the source voltage decreases, the impedance of a parallel RC circuit (SSC – 2009)

Increase

Decrease

Remain Same

Decrease to zero

Answer.2. Decrease

Explanation

In parallel circuit 1/Z = 1/R + 1/Xc.

Since Xc = 1/(2πfc) which is Xc is inversely proportional f.

Thus in the parallel circuit the higher the resistance the lower the total resistance(impedance) therefore if the frequency decrease, the impedance will be decreased.

Ques.98. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 20 Q. If frequency is increased to 100 Hz, reactance becomes_____ohms. (SSC – 2009)

5

5

10

15

Answer.3. 10

Explanation

Capacitive reactance

Xc = 1/2πf

Therefore X_{C1}/X_{C2} = 2πf_{2}/2πf_{1}

= 20/X_{C2} =100/50

= X_{C2} = 10

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