# MCQs on Electronics – page -15

1. A moving coil of a meter has 100 turns, and a length and depth of 10 mm and 20 mm respectively. It is positioned in a uniform radial flux density of 200 mT. The coil carries a current of 50 mA. The torque on the coil is

Torque on the coil T = NBAI
Where N = 100, B = 200 mT, A = Area of the coil = Length × Breadth = 200 × 10-6 sq. mt., I = current through the coil = 50 mA .
Therefore T = 200 μNm.

2. Transient response is improved in case of

Basically a lead network has the improved transient response, good stability and reduced steady state error.

3. Attraction and repulsion type instruments are the two different types of which instrument ?

The attraction and repulsion type instruments are called as moving iron instruments because the soft iron piece is placed in a magnetic field to become strongly magnetized. Hence, due to the attraction or repulsion action happens in the iron piece and thereby it moves. That is why those instruments are also called as moving iron instruments.

4. Speed of data transmission in 4-G network of telecom is

Speed of data transmission in 4G network of telecom is from 100 mbps to 1 gbps.

5. The number of electrons in the outer most orbits of carbon atom is

A Carbon atom has 6 protons, there are 4 electrons orbiting in its outer shell and 2 within its inner shell.

6. In a delta network each element has value R. The value of each element in equivalent star network will be

If the delta connected system has same resistance R at its three sides, then equivalent star resistance REQ will be, REQ = [(R*R) / (R + R + R)] = R/3.

7. A transistor has how many pn junctions?

We know that the transistor has three layers. So, in between the two layers, there must be a junction. Hence, the total number of junctions = number of layers – 1 = 3 – 1 = 2.

8. What is one important thing transistors do?

We know that the transistor can act as an amplifier. The amplifier amplifies the weak signals.

9. Who invented the first junction transistor?

It was invented by William Shockley at Bell Labs on June 23, 1948 (patent filed June 26, 1948).

10. The barrier potential across each silicon depletion layer is

For silicon depletion layer, the barrier potential is 0.7 Volts. For germanium depletion layer, the barrier potential is 0.3 Volts.

11. In an npn transistor, the majority carriers in the emitter are

In an NPN transistor, the majority current carriers are electrons. In a PNP transistor, the majority current carriers are holes.

12. The emitter diode is usually

In typical operation, the base emitter junction is forward biased, which means that the p-doped side of the junction is connected with positive potential and the n-doped side of the junction is connected with negative potential. Hence, the base emitter junction acts as a diode in forward bias and that is why it is called as emitter diode.

13. For normal operation of the transistor, the collector diode has to be

In typical operation, the base collector junction is forward biased, which means that the p-doped side of the junction is connected with negative potential and the n-doped side of the junction is connected with positive potential. Hence, the base collector junction acts as a diode in reverse bias and that is why it is called as collector diode.

14. The base of an npn transistor is thin and

In a NPN transistor, the Base and Collectors are lightly doped because it should accept those charge carriers.

15. Most of the electrons in the base of an npn transistor flow

In an NPN transistor, few electrons are injected by the emitter into the base of the transistor and few electrons are entering the base flow directly through the base to the positive battery terminal. Most of the emitter current of electrons diffuses through the thin base into the collector. Moreover, the small base current produces a larger change in collector current.

16. Most of the electrons in the base of an npn transistor do not recombine because they

Current gain is directly proportional to the recombination lifetime of the electrons in the base and inversely proportional to the base width. In an NPN transistor, the current gain of the electrons in the base is very high. Hence, it has a long lifetime.

17. Most of the electrons that flow through the base will

In an NPN transistor, few electrons are injected by the emitter into the base of the transistor and few electrons are entering the base flow directly through the base to the positive battery terminal. Most of the emitter current of electrons diffuses through the thin base into the collector. Moreover, the small base current produces a larger change in collector current.

18. The beta of a transistor is the ratio of the

The common emitter current gain is represented by beta (β). It is approximately the ratio of the DC collector current to the DC base current in forward active region.

19. Increasing the collector supply voltage will increase

By increasing the collector voltage, the load can get the increased voltage at the output side. It does not disturb any of the above mentioned currents.

20. The fact that there are many free electrons in a transistor emitter region means the emitter is

By increasing the emitter junction efficiently by providing heavy doped substrates, the electrons can be transferred majority of electrons which is emitted from emitter to collector.

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