SSC JE 2013 electrical question paper with solution

24 Comments / SSC previous year solved electrical papers / April 10, 2022

Ques 11.  Phasor diagram of load voltage (V), current in pressure coil (I P ) and current in the current coil (I C ) is shown in the figure when an electrodynamic wattmeter is used to measure power. The reading of the wattmeter will be proportional to

Phasor diagram of load voltage (V), current in pressure coil

  1. cos⁡(β + ψ)
  2. cos⁡ψ
  3. cosβcosψ
  4. cosβcos⁡(β + ψ)

 Answer 3. cosβcosψ

Explanation: 

P = VI cos β. Ic cos ψ

Where β is the angle by which Ip is lagging behind applied voltage V

ψ is the power factor of the load

Therefore the reading of the wattmeter will be proportional to

P  ∝ cos β cos ψ

 

Ques 12. Two parallel conductors carrying current in opposite directions will exert on each other

  1. An attractive force
  2. A repulsive force
  3. An axial force
  4. No force

Answer.2. A repulsive force

Explanation:

  • If the current flowing in the same direction then the conductor attracts each other and if the current flowing in the opposite direction then the conductor generates a repulsive force.

 

Ques 13. The unit of the reluctance of the magnetic circuit is

  1. AT/m
  2. Weber/m
  3. AT/Weber
  4. Weber/AT

Answer.3. AT/Weber

Explanation:

Reluctance is defined as

ℜ = F/Φ

F = magnetomotive force (MMF) in ampere-turns

Φ =  the magnetic flux in webers.

Therefore the unit of Reluctance is ampere-turns per Weber ( AT/Weber) (a unit that is equivalent to turns per Henry)

 

Ques 14. In indicating instrument the springs are mainly used to

  1. Conduct the current on the coil
  2. Hold the pivot in position
  3. Control the pointer movement
  4. Reduce the vibration of the pointer

Answer.3. Control the pointer movement

Explanation:

Spring provides the controlling force in the measuring instrument if the controlling force is absent the pointer will not comes back to starting position i.e zero when the current is removed.

 

Ques 15.  A balanced 3-phase, 3-wire supply feeds balanced star-connected resistors. If one of the resistors is disconnected, then the percentage reduction in load will be

  1. 33.33 %
  2. 50 %
  3. 66.67 %
  4. 75 %

Answer.2. 50

Explanation:

Underbalanced condition P = √3

A balanced 3-phase, 3-wire supply feeds balanced star connected resistors. If one of the resistors is disconnected, then the percentage reduction in load will be

If one of the resistors is disconnected it becomes a single-phase circuit with power

A balanced 3-phase, 3-wire supply feeds balanced star connected resistors. If one of the resistors is disconnected, then the percentage reduction in load will be

 

Ques 16.  The total flux at the end of a long permanent bar magnet is 100×10 -6 Wb.The end of its magnet is withdrawn through a 1000 turn coil in 1/20 seconds. The induced emf in the coil is

  1. 20.0 V
  2. 2.0 V
  3. 0.2 V
  4. 0.02 V

Answer.2. 2.0 V

Explanation:

solution 13

 

Ques 17.  In reference to the figure, the voltage waveform v(t) is measured by a PMMC, a PMMC combined with the bridge rectifier, and a moving iron (MI) instrument. Two lists are provided thereafter

In reference to the figure, the voltage waveform v(t) is measured by a PMMC, a PMMC combined with the bridge rectifier and a moving iron (MI) instrument. Two lists are provided thereafter


  In reference to the figure, the voltage waveform v(t) is measured by a PMMC, a PMMC combined with the bridge rectifier and a moving iron (MI) instrument. Two lists are provided thereafter

The correct option relating to the instrument and their reading is

  1. a-i, b-ii, c-iii
  2. a-iii, b-ii, c-i
  3. a-ii, b-iii, c-i
  4. a-iii, b-i, c-ii

Answer.2. a-iii, b-ii, c-i

Explanation:

PMMC type instrument measure average value

= Area of graph / Total Time

= Area of Graph = 10 x 4 = 40 unit

= Total time = 16 ms

= 40 /16 = 2.5 V

 

Ques 18.  The switching transistor as shown carries on the collector side an RMS current of 8 mA. If the frequency of rectangular pulse train v i is 50 Hz, then the on-time of the transistor is

numerical 3

  1. 20 ms
  2. 6.4 ms
  3. 12.8 ms
  4. 16 ms

 

Ques 19. An ammeter of resistance Rm is placed in an arrangement as shown in the figure. The material of Rm, Rsh is copper whereas that of Rs, Rx is manganin. The condition for which the meter performance is compensated against the temperature is

numerical 4

  1. 1/Rm + 1/Rsh = 1/Rs + 1/Rx
  2. RmRsh = RsRx
  3. Rm + Rsh = RsRx
  4. Rm/Rs =Rsh/Rx

[box type=”info”] Answer 4. Rm/Rs =Rsh/Rx

Explanation:

The condition for which the meter performance is compensated against the temperature will be when the resistance material is equally balanced

RmRx = RshRx

Rm/Rs =Rsh/Rx 

 

Ques 20.  If a 110 V, 50 Hz is supplied across a PMMC voltmeter of full-scale range 0-220 V and internal resistance of 10 kΩ, the reading of the voltmeter will be

  1. 0 V
  2. 110 √2 V
  3. 78 V
  4. 55 V

Answer 1. 0V

For sinusoidal voltage, PMMC reads zero

PMMC type instrument uses two permanent magnets in order to create the stationary magnetic field. If we apply AC current to these types of instruments the direction of current will be reversed during the negative half cycle and hence the direction of torque will also be reversed which gives the average value of torque zero.

Also If a.c. supply given to these instruments, an alternating torque will be developed. Due to the moment of inertia of the moving system, the pointer will not follow the rapidly changing, alternating torque and will fail to show an,y readings 

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