previous year question papers for semester exam.

1. (a) Explain class-A, class-B and class-C amplifiers in detail along with circuit diagram.
(b) Explain the principle of push pull amplifier. Show the circuit of class-B push pull
amplifier and explain its working.
2. (a) Derive an expression for the current flowing through A.C circuit containing R,L C in
series. Derive the formula for resonant frequency and impedance of the circuit.
(b) A series circuit of R= 10Ω, L= 2H and C = 20μF is connected to A.C source of v=50 sin
ωt. Determine the resonant frequency ω₀ and expression for resonant current.
Also show the necessary circuit diagram.
3. (a) What is need of modulation? State various methods of modulation. Explain in detail the
process of amplitude modulation along with circuit diagrams and wave forms.
(b) An A.M wave is represented by the expression v = 5 (1+0.6 cos 6280t) sin 211× 104 t
volts. Then
(i) what are the minimum and maximum amplitudes of the AM waves and
(ii) What frequency components are contained in the modulated wave and what is
amplitude of each component.
4. (a) What is SSB modulation? How would you develop SSB signals.
(b) With the help of detailed block diagram explain the working of A.M transmitter.
5. (a) Why is it necessary to demodulate the modulated signal? Explain the linear diode
detector circuit.
(b) The carrier frequency in F.M modulation is 1000 KHz. If the modulating frequency is
15 KHz what are the first three upper side bands and lower side band frequencies.
6. (a) The impedance Z1=(10+j5) and Z2=(8+j6) are joined in parallel and connected across a
voltage v=200+j0. Determine the circuit current, its phase and branch currents.
(b) In a series circuit containing the resistor and inductor the current and the voltages are
expressed as I(t) = 5 sin (314t + 2π/3) and v(t) = 15 sin (314t + 5π/6). Calculate
(i) impedance of the circuit
(ii) the resistance,
(iii) the inductance
(iv) average power drawn by the circuit and
(v) power factor.
7. Write short notes on any TWO of the following:
(a) RC coupled amplifier.
(b) Balanced slope detector.
(c) Diode modulator circuit.