Basic Electronics - Dec 2011

First Year Engineering (C Cycle) (Semester 1)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.

Choose the correct for the following :-

1 (a) (i) The voltage a which forward current through the diode starts increasing rapidly is called as _____
(A) Saturation voltage
(B) Breakover voltage
(C) cut in voltage
(D) cut off voltage(1 marks) 1 (a) (ii) Dynamic zener resistance is _____ in reverse breakdown condition.
(A) very high
(B) high
(C) zero
(D) very small(1 marks) 1 (a) (iii) Smaller the ripple factor, the output will have higher _____ components.
(A) AC
(B) DC
(C) Both AC and DC
(D) Pulse(1 marks) 1 (a) (iv) The transformer utilization factor of a bridge type full wave rectifier is _____
(A) 0.287
(B) 0.812
(C) 0.864
(D) 0.48(1 marks) 1 (b) Draw the AC equivalent circuit of a diode.(4 marks) 1 (c) With a circuit diagram, explain the working of a centre-tapped FWR.(6 marks) 1 (d) Prove that ripple factor of HWR is 1.21(6 marks)

Choose the correct answer for the following :-

2 (a) (i) The current conduction in bipolar junction transistor is because of _____
(A) Electrons
(B) Holes
(C) Both electrons and holes
(D) current (1 marks) 2 (a) (ii) In cut off region both base-to-collector and base to emitter junctions are _____
(A) forward biased
(B) ON
(C) Reverse biased
(D) None of these(1 marks) 2 (a) (iii) In a transistor I_B=30 mA and I_E=10 mA. What is the value of ? ?
(A) 0.92
(B) 0.99
(C) 0.98
(D) 0.96(1 marks) 2 (a) (iv) In CB-mode of a transistor when the reverse bias voltage increases, the width of depletion region also increases, which reduces the electrical base width calles as _____
(A) Depletion
(B) Early effect
(C) cut in
(D) punch through effect (1 marks) 2 (b) What are the advantages of trasistor over vaccum tube?(4 marks) 2 (c) Draw and explain the input and output characteristics of CE configuration of a transistor.(6 marks) 2 (d) For the CE-circuit shown in fig 2(d), draw the DC load line and obtain Q-point values Assume ?=100 and V_BE=0.7 V

(6 marks)

Choose the correct answer for the following :-

3 (a) (i) Ideally stability factor should be zero to get _____ Q-point.
(A) Unstable
(B) Centre of the cutoff
(C) Stable
(D) None(1 marks) 3 (a) (ii) Which of the following factor affects the Q-point stability?
(A) I_CO
(B) Coupling capacitor
(C) Emitter resistor
(D) Bypass capacitor(1 marks) 3 (a) (iii) In what biasing circuit voltage shunt negative feed back is provided?
(A) Voltage divider biasing
(B) Fixed bias
(C) Collector to base bias
(D) Emitter bias(1 marks) 3 (a) (iv) Fixed bias circuit provides _____ stability
(A) Poor
(B) High
(C) Better
(D) Very good(1 marks) 3 (b) For the circuit shown in fig. I_C=2 mA, ?=100, and V_CE=3V, Calculate R₁ and E_C. Assume V_BE=0.6V.

(8 marks) 3 (c) What factors cause instability of a Q-point? Explain it.(8 marks)

Choose the correct answer for the following :-

4 (a) (i) JFET is a _____ device
(A) Bipolar
(B) Unipolar
(C) Uni-Bipolar
(D) None of these(1 marks) 4 (a) (ii) PNPN device is an _____
(A) UJT
(B) SCR
(C) MOSFET
(D) BJT(1 marks) 4 (a) (iii) The UJT relaxation oscillator is used to generate _____
(A) Square wave signal
(B) Rectangular wave signal
(C) Sine wave signal
(D) Triggering pulse(1 marks) 4 (a) (iv) The holding current in SCR is _____ latching current
(A) More than
(B) Less than
(C) Equal to
(D) None of these(1 marks) 4 (b) Draw the equivalent circuit of a UJT and mention its applications.(4 marks) 4 (c) What are the applications of SCR?(4 marks) 4 (d) Draw the drain characteristics of a n-channel JFET and explain it.(8 marks)

Choose the correct answer for the following :-

5 (a) (i) If the voltage gain of the amplifier is 0.001, what is the value of gain is dB's?
(A) -60
(B) -62
(C) 60
(D) 100(1 marks) 5 (a) (ii) With negative feedback, the bandwidth of an amplifier _____
Decreases
(B) Increases
(C) Both A and B
(D) Constant(1 marks) 5 (a) (iii) In oscillator circuit _____ feedback is used,
(A) Voltage seriers
(B) Positive
(C) Negative
(D) Both +ve and -ve(1 marks) 5 (a) (iv) In RC-phase shift oscillator each section of RC-network produces phase shift of _____
(A) 60°
(B) 30°
(C) 180°
(D) 90°(1 marks) 5 (b) With a neat diagram, explain the operation of Colpitt's oscillator.(8 marks) 5 (c) Explain the operation of single stage RC coupled amplifier and draw its frequency response.(8 marks)

Choose the correct answer for the following :-

6 (a) (i) For a differential amplifier A₄=10000 and CMRR=10⁸. What is the value of A_C?
(A) =10^-4
(B) 10^-6
(C) 10⁴
(D) 100(1 marks) 6 (a) (ii) For an inverting op-amp if R₁=R_F then circuit is called _____
(A) Sign changer
(B) Sign multiplier
(C) +ve sign
(D) None of these (1 marks) 6 (a) (iii) The ideal bandwidth of an op-amp is _____
(A) Zero
(B) Infinity
(C) High
(D) Medium(1 marks) 6 (a) (iv) Buffer and level shifter is usually a
(A) Current follower
(B) Collector follower
(C) Resistance follower
(D) Emitter follower(1 marks) 6 (b) Define the following terms with respect to op-amps
(A) Slew rate
(B) Power supply rejection ratio
(C) CMRR.(6 marks) 6 (c) Derive the expression of output voltage of a op-amp differentiator.(5 marks) 6 (d) Determine the output voltage for the op-amp adder circuit shown in fig.

(5 marks)

Choose the correct answer for the following :-

7 (a) (i) The carrier frequency is _____ modulating frequency
(A) Lower than
(B) Higher than
(C) Equal to
(D) None of these(1 marks) 7 (a) (ii) The bandwidth of AM waves is _____
(A) 2fm
(B) fm
(C) fm/2
(D) None of these(1 marks) 7 (a) (iii) Find the decimal equivalent of (10AB)₁₆.
(A) 3267
(B) 4265
(C) 4268
(D) 4267(1 marks) 7 (a) (iv) What is the binary equivalent of (1126)₈?
(A) 001 001 010 110
(B) 100 001 010 110
(C) 110 110 001 001
(D) 001 001 110 010 (1 marks) 7 (b) Draw the block diagram of superheterodyne receiver and explain the function of each block.(8 marks) 7 (c) Convert (BCDE)₁₆= ( )₂=( )₈=( )₁₀.(3 marks) 7 (d) Subtract (57)₁₀ from (43)₁₀ 2's complement form.(5 marks)

Choose the correct answer for the following :-

8 (a) (i) For NAND-Gate both inputs are high, then output will be _____
(A) High
(B) Low
(C) Tristate
(D) None of these(1 marks) 8 (a) (ii) Y=AB+AB is a Boolean expression for
(A) EX-OR
(B) EX-NAND
(C) EX-NOR
(D) None of these(1 marks) 8 (a) (iii) A+(B+C)=(A+B)+C is a _____ property
(A) Associative
(B) Commutative
(C) Distributive
(D) None of these(1 marks) 8 (a) (iv) The expression Y=AB+BC+BC when simplified is _____
(A) B+C
(B) AB
(C) A+B
(D) AB+C(1 marks) 8 (b) Simplify the following Boolean expression
Y=ABC+ABC+ABC+ABC
Y=(A B+AC)(BC+B C)(ABC)(6 marks) 8 (c) Draw the logic circuit of a full adder and also write its truth table with sum and carry expressions.(6 marks) 8 (d) Realize the expression F=(X+Y(Z+Y)) using only NAND-Gates.(4 marks)