Electronics and Communication MCQ Class XII.pptx

Multiple Choice questions (MCQs) in Electronics and Communication
(Unit - X Class XII TN State Board Syllabus)

1. Electronics and Communication MCQ Class-XII (TN State Board) (With explanation)

2. By Dr M. Arunachalam Head, Department of Physics ( Rtd .) Sri SRNM College, Sattur

3. 1. The barrier potential of a silicon diode is approximately, a) 0.7 V b) 0.3V c) 2.0 V d) 2.2V The barrier potential of a silicon diode is 0.7 V Ans: a

4. 2. If a small amount of antimony (Sb) is added to germanium crystal, a) it becomes a p-type semiconductor b) the antimony becomes an acceptor atom c) there will be more free electrons than hole in the semiconductor d) its resistance is increased Antimony (Sb) is a pentavalent atom from V group of periodic table. So it has excess of electrons. Hence, if antimony (Sb) is added to germanium, the semiconductor will have more free electrons than holes . Ans: c

5. 3. In an unbiased p-n junction, the majority charge carriers (that is, holes) in the p -region diffuse into n -region because of a) the potential difference across the p-n junction b) the higher hole concentration in p -region than that in n-region c) the attraction of free electrons of n -region d) All of the above Holes in p-region diffuse into n-region because of the higher hole concentration in p-region than that in n-region. Ans: b

6. 4. If a positive half –wave rectified voltage is fed to a load resistor, for which part of a cycle there will be current flow through the load? a) 0 –90 b) 90 –180 c) 0 –180 d) 0 – 360 The output of half wave rectifier is shown in the figure. Here current flows through 0 to π only ie . –180 Ans: c

7. 5. The zener diode is primarily used as (a) Rectifier b) Amplifier (c) Oscillator d) Voltage regulator The zener diode is primarily used as Voltage regulator Ans: d

8. 6. The principle based on which a solar cell operates is a) Diffusion b) Recombination c) Photovoltaic action ` d) Carrier flow Solar cell operates on the principle of Photovoltaic action Ans: c

9. 7. The light emitted in an LED is due to a) Recombination of charge carriers b) Reflection of light due to lens action c) Amplification of light falling at the junction d) Large current capacity. Light emitted in an LED is due to the recombination of charge carriers Ans: a

10. 8. The barrier potential of a p-n junction depends on i ) type of semiconductor material ii) amount of doping iii) temperature. Which one of the following is correct? a) ( i ) and (ii) only b) (ii) only c) (ii) and (iii) only d) ( i ) (ii) and (iii) Barrier potential of a p-n junction depends on the type of semiconductor material (For Ge it is 0.3V and for Si it is 0.7V at 25 C. It means it depends on temperature. Also it depends on the amount of doping that decides the width of depletion region. Hence Answer is ( i ) (ii) and (iii) Ans: d

11. 9. To obtain sustained oscillation in an oscillator, a) Feedback should be positive b) Feedback factor must be unity c) Phase shift must be 0 or 2π d) All the above

12. Solution Barkhausen conditions for sustained oscillations: There should be positive feedback The loop phase shift must be 0 or integral multiple of 2π Loop gain ie . lA β l must be unity Hence the answer is All the above Ans: d

13. 10. If the input to the NOT gate is A = 1011, its output is a) 0100 b) 1000 c) 1100 d) 0011 The Boolean expression for NOT gate is y = A Y – Output A - Complement of input A Hence for the input 1011, the output is 0100 Ans: a

14. 11. Which one of the following represents forward bias diode? (a) (b) (c) (d) When a p-n junction diode is forward biased, its p-side is kept at more positive than the n – side. Hence the circuit ( ie 0V at p-side and -2V at n-side) represents forward biased Ans (a)

15. 12. The given electrical network is equivalent to a) AND gate b) OR gate c) NOR gate d) NOT gate

16. Solution NOR NOT NOT Y = A+B Y Y ie . Y = A+B NOR gate Ans: c

17. 13. The output of the following circuit is 1 when the input ABC is a) 101 b) 100 c) 110 d) 010 To get Y = 1, We must have both inputs A+B and C as 1. Of the four answers we have C=1in option (a) only. 101 Ans: a

18. 14. The variation of frequency of carrier wave with respect to the amplitude of the modulating signal is called a) Amplitude modulation b) Frequency modulation c) Phase modulation d) Pulse width modulation By definition, the frequency of the carrier signal ( ie . wave) is modified in proportion to the instantaneous amplitude of the base band signal ( ie . Modulating signal) is called Frequency modulation . Ans: b

19. 15. The frequency range of 3 MHz to 30 MHz is used for a) Ground wave propagation b) Space wave propagation c) Sky wave propagation d) Satellite communication The frequency range for sky wave (or) ionospheric propagation is 3 MHz to 30 MHz Ans: c

20. Thank You