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Electronics and Communication Engineering - Electronic Devices and Circuits

Exercise : Electronic Devices and Circuits - Section 12
46.
A source of angular frequency 1 rad sec has a source impedance consisting of 1 Ω resistance in series with 1 H inductance. The load that will obtained the maximum power transfer is
1 Ω resistance
1 Ω resistance in parallel with 1 H inductance
1 Ω resistance in series with 1 F capacitor
1 Ω resistance in parallel with 1 F capacitor
Answer: Option
Explanation:

According to question Z = R + jωL

ω = 1, L = 1 Z = R + j

max. power transfer will take place when Z = R - j C = 1.

47.
When tracing through a resistance we always get a voltage drop.
True
False
Answer: Option
Explanation:

It depends on direction of current.

48.
A copper coil has a resistance of 40 ohm at 20°C. At 100°C the resistance is likely to be
44 Ω
54 Ω
84 Ω
104 Ω
Answer: Option
Explanation:

Temperature coefficient of copper = 0.00393

R100 = 40 (1 + 0.00393 x 80) 54 Ω

49.

Assertion (A): In a parallel circuit with three branches having R, L and C respectively and fed by a step current I, the current through inductance is always zero.

Reason (R): The time constant of R-L circuit is L/R.

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:

The current through inductance is zero at t = 0 and equal to I at t = ∞.

50.
When a source is delivering maximum power to a load through a network, the ratio of power delivered to the source power
may be 50% or less than 50%
is 50%
may be 50% or more than 50%
may be 50% or more less than 50%
Answer: Option
Explanation:

The network can be replaced by Thevenin's equivalent circuit. The load gets maximum power from the network but Thevenin's theorem does not guarantee that this will be half of maximum power.

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