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Electronics and Communication Engineering - Networks Analysis and Synthesis

Exercise : Networks Analysis and Synthesis - Section 5
11.
In the circuit of figure the voltage across C at t = 0+ is
0 V
20 V
very large
7.5 V
Answer: Option
Explanation:

Voltage across a capacitor cannot change instantaneously.

12.
The frame of electric motor is connected to three plates having earthing resistance of 10 Ω, 20 Ω and 30 Ω respectively. The materials of the three plates are copper, aluminium and iron respectively. The percentage of energy dissipated by 10 Ω earthing plate
is more than 50% of total energy
is less than 50% of total energy
depends on the materials of the three plates
may be more or less than 50% of total energy
Answer: Option
Explanation:

The parallel combination of 30 Ω and 20 Ω is 12 Ω. Since 12 Ω and 10 Ω are in parallel, the 10 ohm plate draws more than 50% current and dissipates more than 50% energy.

13.
In the circuit of figure, the power consumed in resistance R is measured when one source is acting at one time. These values are 18 W, 50 W and 98 W. When all source act together the maximum and minimum power can be
98 W and 18 W
166 W and 18 W
450 W and 2 W
166 W and 2 W
Answer: Option
Explanation:

Let R = 1 Ω.

Then I1 = 32 A, I2 = 52 A and I3 = 72 A.

(I1 + I2 + I3)2 R = (152)2 R = 450 Ω.

14.
The resistance RAB in the circuit is
10 Ω
12 Ω
9 Ω
3 Ω
Answer: Option
Explanation:

(6 + 6/5) || (18 + 18/5) = 5.4

5.4 + 3.6 9 Ω.

15.
In the circuit of figure the current through L at t = ∞ is
0 A
10 A
6.67 A
5.1 A
Answer: Option
Explanation:

At t = ∞ inductance behaves as short-circuit.

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