PHY/VI/12 Student's Copy
2 0 1 8
6th Semester
PHYSICS
TWELFTH PAPER
Advanced Electronics
Pre-revised
Full Marks 55
Time 2½ hours
PART A—OBJECTIVE
Marks 20
The figures in the margin indicate full marks for the questions
SECTION—A
Marks 5
Tick the correct answer in the brackets provided 1×5=5
1. If the doping level of a diode is increased, the breakdown voltage
remains the same
is increased
is decreased
becomes zero
/496 1 Contd.
2. At the base-emitter junction of a transistor, one finds
a reverse bias
a wide depletion layer
low resistance
high resistance
3. If the feedback fraction of an amplifier is 0·01, then the voltage gain with
negative feedback is approximately
500
100
1000
5000
4. In a phase-shift oscillator, the frequency determining elements are
L and C
L and C
R and C
C only
5. As the modulation level is increased, the carrier power
is increased
remains the same
is decreased
becomes infinite
SECTION—B
Marks 15
Give very short answers to the following questions 3×5=15
1. State and explain Kirchhoff's law.
2. Explain the action of Zener diode as a voltage regulator.
3. Why do we use h-parameters to describe a transistor?
4. What is the impact of negative feedback on noise in circuit?
5. What is the difference between high-level and low-level modulations?
PHY/VI/12 2 Contd.
PART B—DESCRIPTIVE
Marks 35
The figures in the margin indicate full marks for the questions
1. Draw the circuit diagram and vector diagram of Anderson bridge. Explain
the working principles to obtain the balance condition.
OR
What are and n-type semiconducting materials? 2
Explain the working of a p-n junction diode under forward bias
condition and define static and dynamic resistances. 5
2. Draw a circuit diagram and explain the working of full-wave rectifier using
semi-conductor diode. Also calculate the average d.c. current through RL
and r.m.s. value of the current.
OR
Explain the working of an transistor. Deduce the relation between a
and b.
3. Explain class-A power amplifier. How is power distributed in it? 3½
Discuss class-B amplifier and calculate its overall efficiency. 3½
OR
Derive the two equations for the hybrid equivalent circuit of a
common-emitter transistor circuit. 7
4. Draw circuit diagram of Hartley oscillator. Explain how it operates. 7
OR
What is Barkhausen criterion for oscillation? 2
Distinguish between sinusoidal and non-sinusoidal oscillators. 2
What are the impacts of positive and negative feedback on input
impedance? 3
PHY/VI/12 3 Contd.
5. What is MOSFET? Explain the principle and operation of enhancement
MOSFET.
OR
What do you mean by amplitude modulation? Obtain expression for
sideband frequencies in AM waves.