Electronics and Communication Engineering - Networks Analysis and Synthesis

31.
The function of a choke in a fluorescent lamp is
at the time of starting only
during the working of time but not at starting time
both at the time of starting and during working
none of the above
Answer: Option
Explanation:

At the time of starting the choke provides a high voltage. During working there is voltage drop across choke so that lamp gets proper voltage.


32.
A series resonant circuit is fed by a voltage having rms value V. At resonance, the voltage across inductance VL and voltage across capacitance VC are related as
VL > VC
VL < VC
VL = VC
VL = 0.5 VC
Answer: Option
Explanation:

At resonance XL = XC. Therefore IXL = IXC or VL = VC.


33.
Calculate i(t) for t ≥ 0, assuming the switch has been in position A for a long time at t = 0, the switch is moved to position B.
1 + e-5 x 103t
e-5 x 103t
1.11 e-5 x 103t
1.11 (1 - e-5 x 103t)
Answer: Option
Explanation:

When switch is in A position, C will be open, t < 0,

i(0-) = = 1.11 mA,

VC(0-) = 3 k x 3.33 volt at t > 0

i(0+) = 1.11 mA, i(t) = A + B e-at

where

5 x 103 at t = 0, A + B = 1.11

t = ∞, A = 0 i(t) = 1.11 e-5 x 103(t) .


34.
In figure, capacitor is uncharged. The switch is closed at t = 0 at t = 0+ di/dt is
100 A/s
-100 A/s
1000 A/s
-1000 A/s
Answer: Option
Explanation:

RC = 10-3, = 0.1 e-1000t. Therefore at t = 0+ equals -100 A/s.


35.
In a series RLC circuit, R = 2 kΩ, L = 1H and The resonant frequency is
2 x 104 Hz
1/p x 104 Hz
104 Hz
2p x 104 Hz
Answer: Option
Explanation:

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