Electronics

06ELN15/25

Model Question Paper Basic Electronics Time: 3 hrs.

Max. Marks:100

Note: 1. Answer any FIVE full question selecting atleast TWO questions from each Part 2. Answer all objective types questions only in first and second writing pages. 3. Objective types questions should not be repeated. PART – A 1

a. i) A Substance for which the width of the forbidden energy is less than 1eV is called a) Conductor b) Semiconductor e) Insulator d) none. ii) A p – n junction diode can be used as a) controlled rectifier b) rectifier c) oscillator d) none. iii) The variation of d.c. output voltage as a function of d.c. load current is called a) circulation b) regulation c) coagulation d) none. iv) The diodes which are designed with adequate power dissipation capabilities to operate in the breakdown region may be employed as _____________devices. a) constant current b) constant voltage c) variable voltage d) variable current (04 Marks) b. Draw the circuit of bridge rectifier and show that ripple factor to a bridge rectifier is 0.48. c. Explain how zener diode can be used as voltage regulator.

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(08 Marks) (08 Marks)

a. i)

In the active region of a common emitter amplifier the base emitter junction is a) forward biased b) reverse biased c) not biased d) none. ii) The arrow in the graphic symbol of transistor defines the direction of ___________ current a) base b) collector c) emitter d) none iii) In the saturation region, the collector base junction is _____________. a) reverse biased b) forward biased c) not biased d) none iv) The stabilization factor ‘S’ is rate of change of collector current with respect to a) saturation current b) reverse saturation current c) emitter current d) none (04 Marks)

b. c.

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Draw input and output characteristics curve of a transistor in common emitter configuration. Explain their nature and shape. What do their slope represent? (08 Marks) Show that a transistor can be used as an amplifier. (08 Marks)

i) The operating point is a fixed point on the characteristic and is called a) P point b) Q point c) D point d) none ii) If the output signal is not faithful reproduction of input, we can say operating point is a) satisfactory b) unsatisfactory c) occasionally satisfactory d) none. iii) Lower stability factors imply lower variations in the ____________currents. a) base b) collector c) emitter d) both base and collector. iv) Reverse saturation current doubles for every______________0C rise in temperature. a) 50 b) 40 c) 30 d) 10 (04 Marks) b. Define biasing of a transistor. Explain with neat circuit the operation of voltage divider (08 Marks) bias circuit. c. For the base bias circuit for a npn transistor, find IB, IC and VCE if RC = 2.2 kΩ, RB = 470kΩ, VCC = 18V, hFE = 100, VBE = 0.7V. Draw the DC load line and indicate Q point. (08 Marks) a.

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i) The SCR is a _______________junction pnpn device. a) 3 b) 4 c) 5 d) 6 ii) Holding current in SCR is ____________ latching current. a) more than b) less than c) equal to d) none iii) BJT is a ____________ controlled device. a) voltage b) current c) power d) both voltage and current iv) FET is a ___________ controlled device. a) current b) voltage c) fire d) solar (04 Marks) b. Draw the complete equivalent circuit of a JFET. Explain each component. (08 Marks) c. Explain basic construction and operation of UJT. Draw the equivalent circuit of UJT. a.

(08 Marks)

PART – B i) If f1 and f2 are two half power frequencies, then bandwidth is given by a) f2 / f1 b) f2 – f1 c) f2 f1 d) f1 + f2 ii) Negative feedback results in ____________ voltage gain. a) increased b) decreased c) zero d) none iii) Oscillations will not be sustained if at the oscillator frequency, the magnitude of the product of the transfer gain of the amplifier and magnitude of the feedback network are __________ than unity. a) less b) more c) equal d) none iv) The frequency stability of an oscillator is a measure of its ability to maintain ___________ frequency as possible over as long a time interval. a) fixed b) variable c) fixed or variable d) none (04 Marks) b. Compare positive feed back and negative feedback amplifier with the help of a neat block diagram. (10 Marks) c. Estimate the values of ‘R’ and ‘C’ for an output frequency of 1kHz in a RC phase shift oscillator. Assume RC = 4kΩ, VCC = 12V, B = 75. (06 Marks)

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a.

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a.

i) If the same input is applied to both the inputs of op-amp then mode is called a) common b) difference c) mixed d) none ii) If Op – amp input is zero and the output reads 25mV then this voltage is called ________ voltage. a) offset b) upset c) cutest d) none iii) Maximum rate at which amplifier output can change in volts per microsecond. (V/µs) is called. a) slew rate b) over rate c) under rate d) none iv) The output impedance of ideal op – amp is (04 Marks) a) 0 b) ∞ c) 10,000Ω d) none b. Draw the circuit of Op - amp as integrator and derive an expression for output voltage. (06 Marks)

c. Draw the noninverting voltage amplifier circuit using an Op – amp expression for closed loop voltage gain.

and derive an (10 Marks)

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(11 011.01)2 = (_________)8. a) 33.2 b) 31.02 c) 32.01 d) none ii) (3580)10 = (__________)16. a) DFC b) FDC c) CDF d) none iii) (11 0 11)2 = (__________)10. a) 25 b) 26 c) 27 d) none iv) 2’s complement of binary number 11 0 11 is (04 Marks) a) 0 0 11 b) 0 1 0 1 c) 0 0 1 0 d) 1 0 0 1 b. Explain the need for modulation. (04 Marks) c. Draw the block diagram of a superheterodyne AM receiver and explain the function of each block. (08 Marks) d. Subtract using 2’s complement [75 – 23]. (04 Marks)

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a.

8

a.

i)

i) Redundancy or absorption theorem states that A + AB = ___________. a) A b) B c) AB d) none ii) Idempotency theorem states that a) A + A = A b) A + A = 1 c) A + A = 0 d) none iii) A + A + AB = ___________. a) 0 b) A c) AB d) none iv) The output is high, when all the inputs are high, such gate is called a) NOR gate b) NOT gate c) AND gate d) NAND gate b. Simplify the following Boolean expressions : i) AB + AC + ABC(AB + AC) ii) AB + A + AB . c. Realize the following expression using basic gates : i) Y = B C + AC + AB ii) Y = ABC + AB + A B C . d. Implement XNOR using only NOR gate.

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(04 Marks) (06 Marks) (06 Marks) (04 Marks)