EL/II/EC/03 Student’s Copy

2024
( CBCS )

( 2nd Semester )

ELECTRONICS

SECOND PAPER

( Semiconductor Physics )

Full Marks : 75
Time : 3 hours

The figures in the margin indicate full marks for the questions

Simple calculator may be used in this paper

( SECTION : A—OBJECTIVE )

( Marks : 10 )

Tick (3) the correct answer in the brackets provided : 1×10=10

1. Addition of impurity to a pure semiconductor is called

(a) rectification ( )

(b) drift current ( )

(c) doping ( )

(d) extrinsic semiconductor ( )

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 2. At room temperature, an intrinsic semiconductor has
(a) many holes only ( )
(b) a few free electrons and holes ( )
(c) many free electrons only ( )
(d) no hole or free electrons ( )

3. An ideal crystal diode is one which behaves as a perfect ______ when

forward biased.
(a) conductor ( )
(b) insulator ( )
(c) resistance material ( )
(d) capacitance material ( )

4. The ripple factor of a full-wave rectifier is

(a) 2 ( )
(b) 1·21 ( )
(c) 2·5 ( )
(d) 0·48 ( )

5. A p-n junction that radiates energy as light instead of as heat is called

(a) LED ( )
(b) photodiode ( )
(c) PIN diode ( )
(d) Zener diode ( )

6. Zener diodes are used primarily as

(a) amplifiers ( )
(b) voltage regulators ( )
(c) rectifiers ( )
(d) oscillators ( )

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 7. In a p-n-p transistor, the current carriers are

(a) acceptor ions ( )

(b) donor ions ( )

(c) holes ( )

(d) free electrons ( )

8. The arrow in the symbol of a transistor indicates the direction of

(a) electron current in the emitter ( )

(b) electron current in the collector ( )

(c) hole current in the emitter ( )

(d) donor ion current ( )

9. The operating point of a transistor is also called

(a) quiescent point ( )

(b) cut-off point ( )

(c) saturation point ( )

(d) intersection point ( )

10. The d.c. load line of a transistor circuit is the line

(a) on the input characteristics ( )

(b) on the output characteristics ( )

(c) along which Q-point shifts up and down ( )

(d) which does not contain the Q-point ( )

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 ( SECTION : B—SHORT ANSWERS )

( Marks : 15 )

Answer the following questions : 3×5=15

UNIT—I
1. Explain the salient features of Bohr’s atomic model.
OR

2. Discuss the formation of hole current.

UNIT—II

3. Explain the different equivalent circuits of a semiconductor diode.

OR

4. What are the important electrical properties of a capacitor and an inductor

in making a filter circuit?
UNIT—III

5. Explain the working of a Zener diode as peak clipper.

OR

6. Describe the construction of thermistor.

UNIT—IV

7. With diagram, explain the working of p-n-p transistor.

OR

8. A transistor has a = 0 × 98, I B = 100 mA and I CO = 6 mA. Calculate I C and I E .

UNIT—V

9. Write down the steps for the construction of d.c. load line.
OR

10. Write a short note on d.c. and a.c. load lines.

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 ( SECTION : C—DESCRIPTIVE )
( Marks : 50 )

Answer the following questions : 10×5=50

UNIT—I

1. (a) With diagram, explain the formation of p-type and n-type

semiconductors. 3+3=6

(b) What is energy band? Explain insulators, conductors and

semiconductors in terms of energy band. 1+3=4
OR
2. (a) From the V-I characteristics of p-n junction diode, explain zero external
voltage, forward bias and reverse bias. 6

(b) Explain the terms break-down voltage and knee voltage. 2+2=4

UNIT—II

3. (a) Explain with a diagram, how semiconductor diode can be used as a

full-wave rectifier. Show that its maximum efficiency is 81·2%. 3+3=6

(b) Describe the filtering action of a choke-input filter. 4

OR
4. (a) What is ripple factor? Derive the value of ripple factor for half-wave and
full-wave rectifiers. 1+3+3=7

(b) Describe the filtering action of a p filter. 3

UNIT—III

5. (a) Explain the working and V-I characteristics of Shockley diode. 2+2=4

(b) Describe the construction and V-I characteristics of Zener diode.

Explain how Zener diode regulates the voltage. 3+3=6

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 OR
6. (a) Describe the operation, characteristics and one application of a
photodiode. 2+2+2=6

(b) Describe the operation voltage and current of LED. 4

UNIT—IV

7. (a) Write a short note on the leakage currents in a transistor for CE

configuration. 6

(b) With diagram, explain the three primary currents which flow in a
properly biased p-n-p transistor. 4
OR

8. (a) Describe common base (CB) transistor’s static characteristics (input,

output and current transfer). 6

a
(b) Show the relation b = , where the symbols have their usual
1-a
meanings. 4

UNIT—V

9. (a) Describe the bandwidth and frequency response curve of an amplifier. 6

(b) Describe class—A, class—B, class—C and class—AB amplifiers. 4

OR

10. (a) Explain input resistance, output resistance, current gain, voltage gain,
power gain of transistor amplifier. 6

(b) Using the output characteristics along with the d.c. load line of CE
transistor circuit, explain the terms cut-off, saturation and active
region. 4

HHH

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