IGNOU BPHET-143 December 2025 Previous Year Question Paper

Q1.Attempt any five parts : 5x2=10

(a) List any four factors that affect the conductivity of semiconductors.

(b) Calculate the maximum input voltage that can be applied to a non-inverting amplifier using op-amp with gain 10 to get distortion free output if supply voltage Vcc is + 15 V.

(c) Convert the hex number BA6x into binary number.

(d) If change in load voltage is 10 mV and nominal load voltage is 10 V, calculate the percentage (%) source regulation of a voltage regulator.

(e) What are the advantages of negative feedback in ampliers ?

(f) Ifthe peak voltage across a transformer secondary is 100 V, what is the dc. voltage value Va of

(i) a half wave rectifier, and

(ii) a full wave rectifier ?

(g) What is CMRR for an op-amp ?

(h) What is the frequency of the displayed signal if one complete cycle covers 5 horizontal divisions on the CRT screen, with a time/div setting of 2us/div ?

Q2.Attempt any two parts: 2x5=10

(a) With a suitable diagram, explain the formation of depletion region in a p-n junction. What happens to the depletion region when the reverse bias voltage is increased ?

(b) What is photovoltaic effect ? Using a suitable diagram, explain the working of a solar cell.

(c) An n-p-n transistor with B = 50 is used in a CE circuit shown in Fig. 1 with Voc = 10 V and Rc = 2 kQ. The self bias is obtained by connecting a 100 kQ resistance (Rg) from collector to base. Assume Vzge = 0.7 V. Determine the Q-point for the circuit : Voo=10V {Ip +Ic Ro=2kQ at kQ Ip] {Ic Fig. 1 :

Q3.Attempt any two parts: 2x5=10

(a) Prove the following Boolean equation using the laws of Boolean algebra : ABC+ABC+ ABC+ABC = AB+BC+AC

(b) For the following logic equation : Y = ABC+ ABC+ABC+ ABC

Q4.Write its truth table.

(ii) Simplify using K-map and draw its circuit after simplification.

(c) Write the truth table of a Full Adder. Simplify the expressions for SUM and CARRY.

Q5.Attempt any two parts: 2x5=10

(a) Plot the frequency response curve for an RC-coupled amplifier with a voltage gain of 1000 in the frequency range 400 Hz to 25 kHz and a 3 dB drop on either side of these frequencies at 80 Hz and 40 kHz. Calculate the gain in dB at the cut-off frequencies also (80 Hz and 40 kHz).

(b) Draw a labelled circuit diagram and explain the working of Colpitts’ oscillator. Write the expression for its frequency of oscillation.

(c) Draw the labelled circuit diagram and derive the expression for voltage gain of inverting amplifier using Op-Amp.

Q6.Attempt any two parts: 2x5=10

(a) Explain with a labelled diagram how a Zener diode can be used for shunt voltage regulation.

(b) Explain briefly the functions of the following components of CRO: = 1+2+2 @) Electron Gun assembly

(ii) Deflection system

(iii) Time base circuit

(c) Draw the circuit diagram of an astable multivibrator using IC 555 timer. Explain its working with the help of associated waveforms. 243 Rp = 100k Q Wear Sara a wre Voo=10V Ig tc Ro=2kQ = ka 8550 23130 + ७480 + ७82 + ABC = AB+BC+AC Y = ABC + ABC+ ABC+ ABC