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Electronics and Communication Engineering - Electronic Devices and Circuits

Exercise : Electronic Devices and Circuits - Section 4
1.
A magnetic circuit has an iron length of 20 cm and air gap length 0.1 cm. If μr = 200 then
mmf for iron and air gap are equal
mmf for iron is much less than that for air gap
mmf for iron is much more than that for air gap
either (a) or (c)
Answer: Option
Explanation:

2.
A circuit is fed by two sources of the same frequency and values 100 ∠0° V and 20 ∠30°V. The current in a particular branch is 5 ∠19° A. If the magnitudes of the sources and changed to 200 ∠0° V and 40 ∠30° V, the current in that branch should be
5 ∠19° A
10 ∠19° A
10 ∠38° A
10 ∠9.5° A
Answer: Option
Explanation:

Since strengths of both sources are doubled, the current would become twice.

3.
Two coils X and Y have self inductances of 5 mH and 10 mH and mutual inductance of 3 mH. If the current in coils X change at a steady rate of 100 A/s, the emf induced in coil Y is
0.3 V
0.5 V
1 V
1.5 V
Answer: Option
Explanation:

4.
Two capacitors of 2 μF and 4 μF capacitance are connected in series across a 30 V dc battery. After the capacitors have been charged, the voltage across them will be
15 V each
10 V and 20 V
20 V and 10 V
30 V each
Answer: Option
Explanation:

Charge will be the same. Since Q = C V voltage will be inversely proportional to Q. Hence 20 V and 10 V.

5.
A 50 Hz current has an amplitude of 10 A. The rate of change of current at t = 0.005 after i = 0 and is increasing is
2221.44 A/s
0
- 2221.44 A/s
- 3141.6 A/s
Answer: Option
Explanation:

i = 10 sin 314.16 t, At t = 0.005, i = 314.16 cos (314.16 x .005) = 0.

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