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

Ques.51.  A series RLC  circuit will have a unity P.F is operated at a frequency of (SSC-2012)

  1. 1/LC
  2. LC
  3. 1/2π√LC
  4. 1/2LC 

Answer.3. 1/2π√LC

Explanation:-

Series RLC circuit will have a unity power factor when resonant will occur.

For resonant, XC = XL

So, 1 / (2π fC) = 2π fL.

f2 = 1/4π2fL

f = 1/2π√LC

 

Ques.52. An electric iron is rated at 230 V, 400 W, 50 Hz. The voltage rating 230 V refers to (SSC-2012)

  1. RMS value
  2. Peak-to-Peak Value
  3. Average Value
  4. Peak Value

Answer.1. RMS value

Explanation:-

In the AC system, we can’t take the average value because the average value is equal to zero over a period in AC.

So now to calculate different parameters like voltage, current, etc we need RMS value. This is the reason why we use RMS quantities while dealing with AC.

 

Ques.53. A sinusoidal periodic waveform is free from DC component, cosine components, and even harmonics. The waveform has (SSC-2012)

  1. Half wave and odd function symmetry
  2. Half wave and even function symmetry
  3. Only odd function symmetry
  4. Only half-wave symmetry

Answer.1. Half wave and odd function symmetry

Explanation:-

Half-wave symmetry implies that the second half of the wave is exactly opposite to the first half. If a waveform has half-wave symmetry, only odd (odd cosine and odd harmonics will be present and DC offset is zero, as one half must exactly cancel out the other. In other words, all even (even cosine and even sine) harmonics will be zero.

 

Ques.54. A periodic train of rectangular pulses x(t) with a time period of 25 seconds has a pulse width of 9 seconds as shown in the figure. The RMS value of the waveform is (SSC-2012)

  1. 10 V
  2. √6 V
  3. 3.6 V
  4. 2.16 V

Answer.3. 3.6 V

Explanation:-

The RMS value of the waveform is

XRMS = Xmax(Ton/T)1/2

6(9/25)1/2

3.6 V

 

Ques.55. The time constant of the network shown in the figure is (SSC-2012)

  1. CR/4
  2. CR/2
  3. CR
  4. 2CR

Answer.3. CR

Explanation:-

Req = (R x R)/R + R = R/2

Ceq = C + C = 2C

Time constant of RC circuit is

τ = RC

τ = (R/2 x 2C) = RC

 

Ques.56. In the series RC circuit, the voltage across C starts increasing, the moment the circuit is switched to V volts DC. The rate of increase of voltage across C at the instant just after the switch is closed (i.e at t = 0t(SSC-2012)

  1. RV/C
  2. CV/R
  3. V/RC
  4. R/CV

Answer.3. V/RC

Explanation:-

Consider an RC circuit at time t =0

The voltage across the capacitor at any time t

 

Ques.57. Form factor of an alternating wave is (SSC-2012)

  1. Form factor = average value/RMS value
  2. Form factor = (RMS value)2/Average value
  3. Form Factor = RMS value/Average value
  4. Form factor = RMS value x Average value

Answer.3. Form Factor = RMS value/Average value

Explanation:-

In Electrical, the form factor of an alternating current waveform (signal) is the ratio of the RMS (root mean square) value to the average value.

 

Ques.58. The phase difference between the following voltage and current waves

V = 311 sin(100πt + 30°) volts and i = 17 sin(100πt – 20°) (SSC-2012)

  1. 20°
  2. 50°
  3. 10°
  4. 30°

Answer.2. 50°

Explanation:-

Phase difference Φ = Φ1 – Φ2

=30 -(-20) = 50°

 

Ques.59. Match the items given in List-I (Material) and those in List-II (Temperature Coefficient of Resistance). Select your answers using codes given in the lists (SSC-2012)

  1. a → R, b → Q, c → P
  2. a → Q, b → P, c → R
  3. a → P, b → Q, c → R

Answer.3. a → R, b → P, c → Q

Explanation:-

  • Temperature coefficient of aluminium is + 0.0034 (positive)
  • Temperature coefficient of manganin is 0.000002 (negligibly small)
  • Temperature coefficient of carbon is −0.0005 (negative)

 

Ques.60. Which of the following material posses the least resistivity? (SSC-2012)

  1. Copper
  2. Manganin
  3. Aluminum
  4. Iron

Answer.1. Copper

Explanation:-

  • The resistivity of the copper is 1.68×10−8
  • The resistivity of the Manganin is 4.82×10−7
  • The resistivity of the Aluminium is 2.65×10−8
  • The resistivity of the Iron is 9.71×10−8

So copper has the least resistivity than Iron, manganin, and aluminum

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