# Objective Questions on Network Analysis 11

1. Find i(t) when VS (t) = 100 sin(2510 t).

2. What is h(t) in following circuit ?

Step response is given as [1 – e -α t]u(t).
h(t) is an impulse response.

3. In a pure parallel LC circuit under resonance condition, current drawn from main supply is

Current in LC circuit is 0 at resonance, because of infinite of parallel LC circuit.

4. Z may comprise of following circuit

Series combination of 2.5 mH and 16 μ F will result in a loss less resonant L-C circuit with constant V.
But parallel combination of 2.5 mH and 16 μF will result in an exponentially increasing sinusoidal response as shown.

5. In a RLC circuit (series) if C is increasing and remaining R and L are constants, then resonant frequency will be

As resonant frequency, f0,

6. If all the transmission zeros of a network are at infinity then it is a

So it will be a low pass filter.

7. At lower half power frequency current in series R-L-C circuit has the phase relation with reference to supply voltage as

8. A circuit with a resistor, inductor and capacitor in series is resonant of f0 Hz. If all the component values are now doubled the new resonant frequency is

9. In a series RLC high Q circuit, the current peaks at a frequency

Now high Q means low R, C and high L.
So bandwidth = f0 / Q.
Since less bandwidth, hence sharp resonance.

10. A sinusoidal voltage V and frequency f connected to a series circuit at variable resistance R and a fixed reactance X. The locus of the tip of the current phase or I as R is varied from zero to infinity is

Above equation is a semicircle equation with radius V / 2X.

11. In the network shown below, switch S was closed and steady state is a attained. If S is opened at t = 0 and i(t) = 2 cos 100t then what is the value of V ?

Circuit starts oscillating when switch is opened.
Here I = 2, R = 2.5 Ω.

12. Circuit shown below has been in steady state when switch S is opened, the current I is given by

When the switch is closed and circuit reached its steady state condition. Since inductor offers short circuit path. So
I = 10 / 1 = 10 A.
Now, when switch is opened,

13. The current i(t) at any instant t in the network shown in the figure will be after closing the switch S at t = 0

The value of the current at t = 0 + and at t = infinity which should be zero and 10 / 1 = 10 A respectively.

14. A series RLC circuit consisting of R = 20 ohms XL = 20 ohms is connected across an AC supply of 200 V rms. The rms voltage across the capacitor is

Z = 20 Ω.
I = 200 / 20 = 10 A.
V C = –JIXC.

15. In a RC circuit consisting R = 10 kΩ and phase angle between current and voltage is 45°. What is the value of C at Ω = 1 ?

So, XC / R = 1.
XC = 10 kΩ.
or, 1 / C = 10 kΩ.

16. In a series RLC circuit the phasor diagram shown as below. Which of following is true regarding phasor diagram for the series RLC circuit ?

17. In a RLC series circuit consisting VR = 3 V, VC = 8 V and VL = 4 V, Find the value of source excitation voltage ?

18. In a parallel RL Circuit has i = 10 A and iR = 8 A. Find the value of current flowing through the inductor ?

19. If a capacitor is added in parallel with inductor C in the above question, which draws a current of 6 A then i will be

20. Consider the following circuit diagram. If R = 25 Ω XL = XC = 25 Ω then what is the value of θ? [ Assuming V as reference phasor. ]

tanθ = XL / R.