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Electronics and Communication Engineering - Electronic Devices and Circuits

Exercise : Electronic Devices and Circuits - Section 9
1.
If P = 250 W and p.f. = 0.707 lagging, Q =
250 vars
- 250 vars
176.7 vars
- 176.75 vars
Answer: Option
Explanation:

Apparent power = , Q = 250 vars and lagging vars are taken as positive.

2.
Figure shows an R-L circuit. The current is i = 1 - e-t. The rate of change of current at t = 1 second is
1 A/s
0.63 A/s
0.37 A/s
0
Answer: Option
Explanation:

3.

Assertion (A): Energy stored in inductance is and that in capacitance is

Reason (R): Inductance and capacitance are dual of each other.

Both A and R are true and R is correct explanation of A
Both A and R are true and R is not the correct explanation of A
A is true but R is false
A is false but R is true
Answer: Option
Explanation:

In principle of duality L is dual of C and I is dual of V.

4.
The time constant of the circuit after the switch shown in the figure is opened is
0.2 s
5 s
0.1 s
dependent on R and hence cannot be determined unless R is known
Answer: Option
Explanation:

.

5.
A series RLC circuit is at resonance at 200 Hz. If capacitance is increased to four times, the circuit will be in resonance at
200 Hz
400 Hz
100 Hz
800 Hz
Answer: Option
Explanation:

. If C becomes four times, f is reduced to half.

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