51. A balanced star-connected load with impedance of 20 ∠– 300 ohm is supplied from a 3-phase, 4-wire, 173 volts system, the voltages to neutral being 100 ∠– 900, 100 ∠– 300 and 100 ∠– 1500 V. The current in the neutral wire is _______ A
    

1. 1. 1

   
   
   

   2. 2

   
   
   

   3. 3

   
   
   

   4. None of the above

   
   
   

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1. View Hint View Answer Discuss in Forum

   Since applied 3-phase voltage is balanced and the impedances are all equal, the currents also would be balanced, as a result there is no current in the neutral wire.

   Correct Option: D

   Since applied 3-phase voltage is balanced and the impedances are all equal, the currents also would be balanced, as a result there is no current in the neutral wire.

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52. The voltage transfer ratio V₂/ V₁ for the network shown in the figure is ________
    

1. 1. 0

   
   
   

   2. 2 / 13

   
   
   

   3. 1

   
   
   

   4. 13 / 2

   
   
   

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1. View Hint View Answer Discuss in Forum

   Assume a current flowing as shown.
   
   V₂ = 1 × 4 = 4V.
   

   I1 =	4	= 2A
   	2

   
   I ₂ = 2 + 1 = 3 A.
   V_A = V₂ + 3 × 2
   = 4 + 6 = 10 V.
   

   I3 =	10	= 5 A
   	2

   
   I ₄ = I₃ + I₂ = 8A.
   V₂ = V_A + 8 × 2
   = 10 + 16 = 26 V.
   

   	V2	=	4	=	2
   	V1		26		13

   
   

   Correct Option: B

   Assume a current flowing as shown.
   
   V₂ = 1 × 4 = 4V.
   

   I1 =	4	= 2A
   	2

   
   I ₂ = 2 + 1 = 3 A.
   V_A = V₂ + 3 × 2
   = 4 + 6 = 10 V.
   

   I3 =	10	= 5 A
   	2

   
   I ₄ = I₃ + I₂ = 8A.
   V₂ = V_A + 8 × 2
   = 10 + 16 = 26 V.
   

   	V2	=	4	=	2
   	V1		26		13

   
   

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53. The v-i characteristics as seen from the terminal pair (A, B) of the network of Fig. (a) is shown in the Fig. (b). If an inductance of value 6 mH is connected across the terminal-pair (A, B), the time constant of the system will be _______μ sec
    

1. 1. 0

   
   
   

   2. 1

   
   
   

   3. 2

   
   
   

   4. 3

   
   
   

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1. View Hint View Answer Discuss in Forum

   The network, as viewed across the terminals can be described by
   v = 8 – i × 200
   ∴ R_int = 2000 ohms.
   

   Time constant of the system becomes, T =	L	=	6 × 10-3	= 3 μs
   	R		2 × 103

   
   

   Correct Option: D

   The network, as viewed across the terminals can be described by
   v = 8 – i × 200
   ∴ R_int = 2000 ohms.
   

   Time constant of the system becomes, T =	L	=	6 × 10-3	= 3 μs
   	R		2 × 103

   
   

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54. In the circuit shown in the figure, if the power consumed by the 5 ohm resistor is 10 W, then the power factor of the circuit is _______
    

1. 1. 1.06

   
   
   

   2. 0.6

   
   
   

   3. 0.06

   
   
   

   4. 1.6

   
   
   

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1. View Hint View Answer Discuss in Forum

   Power consumed by 5 ohm resistor = 10 W
   

   ∴ Current, I =	√P
   	√R

   
   

   =	√10	= √2 A
   	√5

   
   Power consumed by the 10 ohm resistor = 2 × 10 = 20 W
   Total power consumed = 30 W
   

   Circuit volt ampere =	50	× √2 = 50 W
   	√2

   
   

   ∴ Power factor =	30	= 0.6 (lagging)
   	50

   Correct Option: B

   Power consumed by 5 ohm resistor = 10 W
   

   ∴ Current, I =	√P
   	√R

   
   

   =	√10	= √2 A
   	√5

   
   Power consumed by the 10 ohm resistor = 2 × 10 = 20 W
   Total power consumed = 30 W
   

   Circuit volt ampere =	50	× √2 = 50 W
   	√2

   
   

   ∴ Power factor =	30	= 0.6 (lagging)
   	50

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55. In the circuit shown in the figure, i(t) is a unit step current. The steady-state value of v(t) is _______ .
    

1. 1. 0.1 Volt

   
   
   

   2. 0.4 Volt

   
   
   

   3. 1.1 Volt

   
   
   

   4. None of the above

   
   
   

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1. View Hint View Answer Discuss in Forum

   At steady state, since capacitor is open and inductor short circuited, therefore current through	1	Ω
   	8

   
   
   

   and V(t) =	4	×	1	= 0.1 Volt
   	5		8

   
   

   Correct Option: A

   At steady state, since capacitor is open and inductor short circuited, therefore current through	1	Ω
   	8

   
   
   

   and V(t) =	4	×	1	= 0.1 Volt
   	5		8

   
   

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