Basic Electronics - Jan 2013

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 answer:

1 (a) (i) A device which allows the current flow in one direction but does not allow it in the opposite direction is called ____
a) Transistor
b) Filter
c) Regulator
d) Rectifier(1 marks) 1 (a) (ii) The capacitance of a forward biased p-n junction is called ____
a) Diffusion
b) Conventional
c) Drift
d) Transition(1 marks) 1 (a) (iii) The zener power dissipation is given by the product of ____
a) V_R, I_Z
b) V_F, I_Z
c) V_Z, I_Z
d) None of these(1 marks) 1 (a) (iv) The maximum efficiency of a full wave rectifier is ____
a) 40.6%
b) 60.4%
c) 78.5%
d) 81.2%(1 marks) 1 (b) Explain the forward and reverse characteristics for a Ge-diode, with a neat figure.(5 marks) 1 (c) With a circuit diagram, explain the working of a full wave rectifier. Draw relevant waveforms.(6 marks) 1 (d) A 9V reference source is to be designed using a zener diode and a resistor connected in series to a 30V supply. Select suitable components and calculate the circuit current when the supply voltage drops to 27V. Assume I_ZT=200mA.(5 marks)

Choose the correct answer:

2 (a) (i) A transistor is cutoff when _____
a) Both emitter and collector junction reverse biased.
b) The emitter junction is reverse biased but the collector junction is forward biased.
c) Both emitter and collector junction are forward biased.
d) The emitter junction is forward biased but the collector junction is reverse biased.(1 marks) 2 (a) (ii) If ?=0.95, then the value of ? of the transistor is ____
a) 0.05
b) 19
c) 100
d) 120(1 marks) 2 (a) (iii) The output characteristics of CE configuration is a graph between:
a) V_BE, I_B
b) V_BE, V_CE
c) V_CE, I_C
d) V_BE, I_E(1 marks) 2 (a) (iv) The Q-point is also known as:
a) Open point
b) Operating point
c) D.C. point
d) A.C. point(1 marks) 2 (b) Explain the working of current amplification using transistor.(5 marks) 2 (c) Explain with the help of circuit diagram the working of input and output characteristics of transistor in CB configuration.(7 marks) 2 (d) For a certain transistor circuit I_C=12.42mA and I_B=200�A
find:
i) I_E
ii) ? and ? of transistor.(4 marks)

Choose the correct answer:

3 (a) (i) In the biasing circuit, the one which gives the most stable operating point.
a) Base bias
b) Collector to base bias
c) Voltage divider bias
d) None of these(1 marks) 3 (a) (ii) Stability factor S for base bias circuit is ____
a) S=1+?
b) S= 1-?
c) S=1/(1-?)
d) S=1/(1+?)(1 marks) 3 (a) (iii) Diode can be used for compensation of ____ changes in voltage divider bias circuit.
a) V_BE
b) V_CE
c) V_CC
d) V_E(1 marks) 3 (a) (iv) In emitter bias circuit ____ is connected between emitter and ground.
a) Inductor
b) Capacitor
c) Resistor
d) Diode(1 marks) 3 (b) With a circuit diagram, explain the operation of collector-to-base bias circuit.(8 marks) 3 (c) The voltage divider bias circuit has V_CC=15V, R₁=6.8k?, R₂=3.3k?, R_C=900?, R_E=900? and h_FE=50, V_BE=0.7V. Find the levels of V_E, I_B, I_C, V_CE and V_C. Draw the DC load line and mark the Q-point on it.(8 marks)

Choose the correct answer:

4 (a) (i) SCR is a ____ device.
a) NPN
b) PNP
c) PNPN
d) PNN(1 marks) 4 (a) (ii) SCR crowbar circuit is used for protection against
a) Under voltage
b) Over current
c) Under current
d) Over voltage(1 marks) 4 (a) (iii) The intrinsic stand-off ratio of UJT ____
a) Must be less than unity
b) Must be greater than unity
c) Must be zero
d) Must be negative(1 marks) 4 (a) (iv) FET is a ____ controlled device.
a) Voltage
b) Current
c) Power
d) None of these(1 marks) 4 (b) Explain the working of two transistor model of SCR.(6 marks) 4 (c) Explain with a neat figure the construction of a p-channel JFET.(6 marks) 4 (d) Give the equivalent circuit of UJT.(4 marks)

Choose the correct answer:

5 (a) (i) In an oscillator we use ____ feedback.
a) Positive
b) Negative
c) Neither
d) Unity gain(1 marks) 5 (a) (ii) The two Barkhausen conditions to be satisfied by oscillator are ____
a) |A?| ? 1, shift = 0°
b) |A?| ? 1, shift = 0°
c) |A?| ? 1, shift = 90°
d) |A?| ? 1, shift =180°(1 marks) 5 (a) (iii) In a RC couple amplifier the DC component is blocked by ____
a) Load resistance R_L
b) Coupling capacitor C_C
c) R_B
d) The transistor(1 marks) 5 (a) (iv) f₁(f_L) and f₂(f_H) are known as ____ frequencies.
a) half
b) half power
c) decibel
d) mid band(1 marks) 5 (b) With the help of circuit diagram, explain the working of a RC couple single stage CE amplifier.(6 marks) 5 (c) List the advantages of negative feedback.(5 marks) 5 (d) Calculate the value of an inductor to be used in Colpitt's oscillator to generate a frequency of 10 MHz. Assume C₁=100 pF and C₂=50 pF.(5 marks)

Choose the correct answer:

6 (a) (i) The ideal value of CMRR is ____
a) 90 dB
b) 2×10⁵
c) 0
d) ?(1 marks) 6 (a) (ii) The PSRR is generally measure in ____
a) dB
b) mV/V
c) �V/V
d) V/�s(1 marks) 6 (a) (iii) The gain of voltage follower is ____
a) Zero
b) Infinite
c) Negative
d) Unity(1 marks) 6 (a) (iv) If we apply a square waveform to a differentiator, then we get ____ at the output.
a) Cosine wave
b) Ramp
c) Sine wave
d) Train of impulses(1 marks) 6 (b) Give the characteristics of an ideal op-amp.(5 marks) 6 (c) With the help of circuit diagram, explain the working of an op-amp as an integrator.(6 marks) 6 (d) Design an adder circuit using op-amp to obtain an output expression. V_O=-(0.1V₁+0.5V₂+20V₃), where V₁, V₂, V₃ are the inputs. Select R_F=10k?.(5 marks)

Choose the correct answer:

7 (a) (i) Over modulation exists when modulation index is ____
a) 1
b) 0
c) >1
d) <1(1 marks) 7 (a) (ii) The relation between carrier power and total power in an AM wave is ____
a) P_C=P_T(1+(m²/4))
b) P_C=P_T(1+(m²/2))
c) P_T=P_C(1+(m²/4))
d) P_T=P_C(1+(m²/2))(1 marks) 7 (a) (iii) The amplitude of both the side bands in an AM wave is ____
a) E_C²/2m
b) m²E_C/2
c) mE_C/2
d) m²E_C²/4(1 marks) 7 (a) (iv) Hexadecimal and octal numbering systems are similar for the first
a) 9 digits
b) 8 digits
c) 7 digits
d) 6 digits(1 marks) 7 (b) Explain the need for modulation.(6 marks) 7 (c) With the help of a block diagram, explain the working of a super heterodyne receiver.(6 marks) 7 (d) Perform the following decimal subtraction using 9's complement method:
i) 49-24
ii) 321-579(4 marks)

Choose the correct answer:

8 (a) (i) For EX-NOR gate the output is 1 if ____
a) Even number of inputs is 0.
b) Even number of inputs is 1.
c) Odd number of inputs is 0.
d) Odd number of inputs is 1.(1 marks) 8 (a) (ii) Which of the following are universal gates?
a) Only NOR
b) Only NAND
c) Both NOR&NAND
d) NOT, AND, OR(1 marks) 8 (a) (iii) The result of binary addition 1+1+1 is ____
a) carry 0, sum 0
b) carry 0, sum 1
c) carry 1, sum 0
d) carry 1, sum 1(1 marks) 8 (a) (iv) A half adder has ____ inputs and <u> </u> outputs.
a) 1,1
b) 1,2
c) 2,1
d) 2,2(1 marks) 8 (b) State DeMorgan's theorem(4 marks) 8 (c) Simplify the following Boolean expressions:
i) Y=AB+A'C+BC
ii) Y=(A+B'+C')(A+B'+C)
iii) Y=C(B+C)(A+B+C)(6 marks) 8 (d) What is a full adder? Give its truth-table, implement the full adder using logic gates.(6 marks)