GOVERNMENT OF KARNATAKA
KARNATAKA STATE PRE-UNIVERSITY EDUCATION EXAMINATION BOARD
II YEAR PUC EXAMINATION – MARCH-2013
SCHEME OF VALUATION
Subject Code: 40
Subject: ELECTRONICS
Qn.
No.
01.
Ans
02.
Ans
03.
Ans
04.
Ans
05.
Ans
06.
Ans
07.
Ans
08.
Ans
09.
Ans
10.
Ans
PART - A
What does the arrow mark indicate in the symbolic representation of a transistor?
Conventional current flow.
Name the transistor amplifier which has very high input impedance.
CC amplifier.
What happens to the distortion of the amplifier when negative feedback is given
to it?
Decreases or reduces.
What is the value of output voltage if both the input voltages are equal in the case
of ideal differential amplifier?
Zero OR non-zero OR two times input
Between LC and RC oscillators, which is preferred for generating low frequency?
RC Oscillator
Define skip zone
Skip zone: The region where there is no reception of any signal, i.e., silent zone.
Write the expression for modulation index in terms of Vmax and Vmin.
Marks
Allotted
1
1
1
1
1
Write the output of XOR gate, when the inputs are A = 0 and B = 1
1 or high
Write the excess-3 code for (201)10.
0101 0011 0100
What is voice mail?
Voice mail is an electronic telecommunication system that records, stores and
delivers voice messages.
OR
Voice mail is a device (answering machine) that records and retrieves audio
messages and play announcements to callers.
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
PART - B
11.
Ans
A transistor has α = 0.98. If Ic = 5 mA, find IB.
= IE/IC, hence IE = 5 mA/0.98 = 5.1 mA
2
1
IB = IE – IC = (5.102 – 5)m = 0.1 mA
1
Page 1
ELECTRONICS
Qn.
No.
Ans
12.
Ans
13.
Ans
Marks
Allotted
OR
β = α/(1 - α) = 0.98 / (1 - 0.98) = 49
1
β = IC/IB , hence IB = 5 mA / 49 = 0.102 mA = 102 µA
Draw the frequency response curve of a CE amplifier. Mention its bandwidth.
1
2
1
Band Width = fH - fL
1
2
Draw the circuit diagram of CC amplifier. Draw the input and output waveforms.
1
1
14.
Ans
15.
Ans
16.
Input
Output
Distinguish between positive feedback and negative feedback.
Positive feedback
Negative feedback
1. Feedback voltage in phase with
Feedback voltage out of phase with
the input
the input
2. Af = A / (1 - Aβ)
Af = A / (1 + Aβ)
3. Noise and distortion increases
Noise and distortion decreases
4. Gain increases
Gain decreases
Any two, 1 mark each.
Mention any two applications of a comparator
1. Zero crossing detector
2. Schmitt trigger
3. Phase detector
4. Voltage level detector
5. Oscillator
Any two applications, 1 mark each.
Draw the circuit symbol and electrical equivalent circuit of a crystal.
2
2
2
2
2
Page 2
Qn.
No.
Ans
17.
Ans
18.
Ans
ELECTRONICS
Marks
Allotted
1
Circuit symbol of crystal
Electrical equivalent circuit of crystal
1
What are sky waves and space waves?
EM waves sent towards the sky which get reflected by the ionosphere and return
back to the earth surface is called sky wave.
2
1
Line of sight waves are called space waves.
OR
The radio waves that are transmitted in the troposphere are called space waves.
OR
The radio waves which penetrate the ionosphere, get reflected by satellite and
reach the earth surface is called as space waves.
Draw the block diagram of AM transmitter
1
2
2
19.
Ans
20.
Ans
Distinguish between latch and flip-flop
2
Latch
Flip-Flop
1. Store data temporarily
Store data permanently
2. Clock is not required
Clock is required
Draw the logic diagram of full adder using 3-input XOR gate and basic gates
1
1
2
1
1
Page 3
Qn.
No.
21.
21.
Ans
ELECTRONICS
The truth table of a gate is given below. Identify the gate and write its logic
symbol.
Inputs
Output
A
B
Y
0
0
1
1
0
0
0
1
0
1
1
1
X-NOR gate
Marks
Allotted
2
1
1
22.
22
Ans
Name the two techniques that increases channel capacity in mobile
communication
Frequency reuse
Cell splitting
2
1
1
PART – C
23.
Using the following data, calculate the experimental and theoretical values of
voltage gain for an Op-Amp non-inverting amplifier.
Input Vi = 0.5 V
Sl. No.
Ri in kΩ
1
2
23.
Ans
2.2
1.2
Rf in kΩ
V0 in volts
8.2
5.6
4
Voltage gain
Theoretical Practical
2.36
2.83
AVT =
1
AVP = Vo / Vi
1
AVT1 = 1 + (8.2 k / 2.2 k) = 4.72 ,
AVP1 = 2.36 / 0.5 = 4.72
1
AVT2 = 1 + (5.6 k / 1.2 k) = 5.66 ,
AVP2 = 2.83 / 0.5 = 5.66
1
OR
23.
23
Ans
The output waveform of Wien-bridge oscillator is shown below. Calculate the
value of resistance when C = 0.01µF (Consider R1 = R2 = R and C1 = C2 = C)
=
4
1
= 1 kHz
OR
1
Page 4
ELECTRONICS
Qn.
No.
Marks
Allotted
1
R = 15.923 kΩ
24.
1
Find the input base resistance and voltage gain of the CE transistor amplifier for
the data given below:
R1 = 47 kΩ, R2 = 12 kΩ, RC = 3.3 kΩ, RE = 1 kΩ, RL = 10 kΩ,
4
Vcc = 18 V, β = 100, VBE = 0.7 V and re’ = (52mV / IE)
24.
Ans
V2 =
=
(
)
= 3.66 V
VE
= 3.66 – 0.7 = 2.96 V
IE
= VE / RE = 2.96 / 1k = 2.96 mA
re’
= 52 mA / 2.96 mA
= 17.56 Ω
1
1
Zin base = β re’ = 100 x 17.56 = 1756Ω
Av
25.
25.
Ans
= - (Rc || RL) / re’
1
= - (3.3k || 10k) / 17.56
= -141.29
Draw the circuit diagram of RC coupled amplifier. Mention its two advantages
1
4
2
Any two advantages, 1 mark each.
1. It is less costly
2. It has wide frequency response
3. It provides less frequency distortion
4. It has no coils or transformers
5. Overall gain is high
2
Page 5
Qn.
No.
26.
Ans
ELECTRONICS
Marks
Allotted
4
An amplifier has an open gain of 150 and bandwidth of 200 kHz. Calculate its
gain and bandwidth after 4% negative feedback.
Af
= A / (1 + Aβ)
= 150 / (1 + (150 x 0.04)) = 21.42
BWf = (1 + Aβ) BW
= (1 + (150 x 0.04)) 200k = 1.4 MHz
1
1
1
1
OR
BWf
27.
= A BW / Af
= (150 x 100k) / 21.42 = 1.4 MHz
1
1
With a circuit diagram, derive an expression for the output voltage of an Op-Amp
subtractor
4
Ans
1
Let Vo1 be the output, with input V1 acting alone, assuming V2 = 0
1
------------------- (1)
Let Vo2 be the output, with input V2 acting alone, assuming V1 = 0
(
Vo
)
-------------------- (2)
1
= Vo1 + V02
If R2 = R1 and R3 = Rf, then,
=
+
1
If Rf = R1 = R, then Vo = V2 – V1
Page 6
Qn.
No.
28.
ELECTRONICS
Marks
Allotted
A Hartley oscillator oscillates at 15 kHz. If the capacitor in tank circuit has a
value of 0.01 µF and one of the inductors is 1 mH, calculate the value of the other
inductor.
4
)
√(
(
1
)
√(
1
)
1
= 0.01126 H
29.
Hence L2 = 0.01126 H – 0.001 H = 0.01026 mH = 10 mH
1
Draw the amplitude modulated waveform. Derive an expression for the
instantaneous voltage of an AM wave.
4
29.
Ans
1
Instantaneous voltage of modulating signal, vm = Vm Sin mt
1
Instantaneous voltage of carrier signal, vc = Vc Sin ct
Vm and Vc are maximum amplitudes of modulating and carrier signals
respectively.
Instantaneous voltage of amplitude modulated wave
vAM = (Vc + vm) Sin ct
= (Vc + Vm Sin mt) Sin ct
= Vc (1 + ma Sin mt) Sin ct
because, (Vm / Vc) = ma
1
Where ma is the modulation index.
(
)
(
1
)
Page 7
Qn.
No.
30.
ELECTRONICS
Marks
Allotted
4
With a circuit diagram, explain the working of linear diode detector.
Circuit Diagram:
1
31.
Working:
 Diode D rectifies AM wave.
 Capacitor C2 provides low reactance to carrier and high reactance to signal.
 Resistor R provides discharging path to C2.
 Capacitor C adds zero level to detected signal.
Simplify the following Boolean expression by using K-map,
Y = f(A, B, C, D) = ∑m(0, 1, 2, 4, 5, 8, 9, 10, 12, 13). Draw the logic circuit for
the simplified expression using only NAND gates.
Ans
Y = f(A, B, C, D) = ∑m(0, 1, 2, 4, 5, 8, 9, 10, 12, 13)
32.
Draw the PIN diagram of IC-741. Describe an experiment to study Op-Amp
adder.
3
4
PART – D
6
Page 8
Qn.
No.
32.
Ans
ELECTRONICS
Marks
Allotted
PIN Diagram:
1
Aim: To construct an op-amp adder and to compare theoretical and practical
values of the output voltages (for DC inputs).
Equipments and Components: Dual power supply ±12 V, variable RPS, resistors,
IC 741, voltmeter
Circuit Diagram:
1
Procedure:
1. Rig up the circuit as shown in figure
2. Set the different values of V1 and V2 and record the output voltages
2
Tabular column or observation:
Input voltage
(in volts)
V1
V2
Theoretical o/p voltage
(in volts)
Vo = - ( V1 + V2)
Practical o/p voltage
(in volts)
1
1
Result: The theoretical and practical values are agreeing with each other.
Page 9
ELECTRONICS
Qn.
No.
32.
32.
Ans
Marks
Allotted
OR
Draw the pin configuration of IC 7400. Describe an experiment to realize halfadder using NAND gates.
PIN diagram of IC 7400:
6
1
Aim: To construct half adder using IC7400 and to verify its truth table.
Equipments and components: Digital trainer kit, IC7400, LED, RPS 5V
Logic Diagram:
1
Procedure:
1. Rig up the circuit as shown in figure.
2. For various combinations of inputs A and B, as given in the truth table,
the logic levels at the output are verified, by on and off of LEDs.
Inputs
Outputs
LED response
A
B
Sum
Carry
Sum
Carry
0
0
0
0
Off
Off
0
1
1
0
On
Off
1
0
1
0
On
Off
1
1
0
1
Off
On
2
1
1
Result: Truth table of the half adder is verified.
Page 10
Qn.
No.
33.
ELECTRONICS
With the circuit diagram, describe the procedure to draw input and output
characteristic curves of a transistor in CB configuration.
Marks
Allotted
6
Ans
2
CB Amplifier
Input characteristics:
1. Set VCB constant.
2. Set different values of VEB and find the corresponding values of IE.
3. Plot the graph of IE versus VEB
1
1
Output Characteristics:
1. Set IE constant
2. Set different values of VCB and find the corresponding values of IC.
3. Plot the graph of IC versus VCB.
1
1
Page 11
Qn.
No.
34a.
34a.
Ans
ELECTRONICS
What is dark current? Draw the circuit diagram of opto-coupler. Mention its one
application.
When there is no incident light a small, thermally generated collector to emitter
leakage current, ICEO flows. This is called dark current.
Marks
Allotted
4
1
Circuit diagram:
2
34b.
34b.
Ans
Applications (any one).
1. For telephone line coupling
2. In audio applications
3. In peripheral equipment isolation
A single stage CE amplifier has a gain of 60 dB. If the input signal is 40 mV,
calculate the output voltage.
60 dB = 20 log Av
Av
= 1000
Av
35a.
Ans
1
2
1
= Vo / Vi
Hence Vo = 40 x 10-3 x 1000 = 40 V
What is an integrator? Draw the circuit diagram and obtain an expression for its
output voltage.
The circuit whose output is proportional to the integral of the input is referred to
as an integrator.
Circuit Diagram:
1
4
1
1
Page 12
ELECTRONICS
Qn.
No.
From the figure
Therefore,
if = ii
if = dQ/dt = Cd(V0 - VG)/dt = Cd(V0)/dt
ii = (VG-Vi)/R = -Vi/R
Cd(V0)/dt = -Vi/R
V0  -
Marks
Allotted
..…..(1)
…….(2)
……(3)
1
1
 Vi dt
RC
(Proper steps must be considered)
1
35b.
Calculate the output voltage in the circuit shown below:
2
35b.
Ans
Note: If the quastion number (35b) is written by the student, full (2) marks must be
awarded because signs of inverting and non inverting terminals of the first op-amp
is printed wrongly in question paper.
2
36a.
With a circuit diagram, explain the working of phase shift oscillator. Write the
expression for frequency of oscillations.
Circuit diagram:
Ans
4
1
1
√
3 RC sections produce a phase shift of 60o each and the total phase shift is 180o in
the RC network.
The op-amp inverting amplifier introduces a phase shift of 180o between its input
and output.
Total phase shift is 360o and loop gain Aβ = 1, which are required for the
sustained oscillations.
Page 13
1
1
Qn.
No.
36b.
ELECTRONICS
Marks
Allotted
2
Calculate the feedback factor in the tank circuit shown below.
C1 = 1 µF, C2 = 10 µF, L = 2 mH
36.b
Ans
37a.
37a.
Ans
37b.
37b.
Ans
38a.
38a.
Ans
β = C1 / C2
1
= 1µ / 10µ = 0.1
Draw the block diagram of FM receiver. Mention two advantages of FM.
Block diagram:
1
4
2
Any two advantages: (1 mark each)
1. All transmitted power is useful.
2. Noise supression is better than AM
3. Signal interference from adjacent channel is very less
4. Signal to noise ratio is high
A 50 MHz carrier is modulated by a 40 Hz audio signal. If the carrier voltage is
4V, and the maximum deviation is 10 kHz, calculate the bandwidth.
BW = 2 (  + fm)
2
2
1
1
4
= 2 (10 k + 400) = 20.8 kHz
Draw the block diagram of digital computer. Explain the function of ALU and
memory unit.
Block diagram:
\
2
Page 14
ELECTRONICS
Qn.
No.
ALU: Arithmetic Logic Unit is designed to perform basic arithmetic operations
(add, subtract), logical operations (AND, OR, etc)
Marks
Allotted
1
Memory unit: The function of the memory unit is to store programs and data.
38b.
Ans.
̅
̅ (
39a.
39a.
Ans
̅
Express the expression
1
̅ into canonical SOP form.
2
̅
̅)
̅(
̅)
̅
̅ ̅
̅
̅
̅ ̅
̅
1
̅ ̅
1
With a block diagram, explain the working of RS flip-flop
Block diagram:
4
1
The output of an RS flip-flop remains in the same state as long as the clock pulse
is zero, regardless of the R&S inputs.
1. When clock=1, R=0, S=0, the output remains in the previous state.
2. When clock=1, R=1, S=0, the output is reset
3. When clock=1, R=0, S=1, the output is set
4. When clock=1, R=1, S=1, the output is in forbidden state
39b.
Ans
Truth table:
Inputs
Output
Clock
State
̅
S
R
Q
X
X
NC
NC
0
Remains in the previous state
0
0
NC
NC
1
Remains in the previous state
1
0
1
0
1
SET
0
1
0
1
1
RESET
1
1
1?
1?
1
Forbidden or invalid condition
Construct OR and AND gates using NOR gates
OR Gate using NOR gate
1
1
1
2
1
Page 15
ELECTRONICS
Qn.
No.
Marks
Allotted
AND Gate using NOR gate
1
40a.
Ans
Draw the block diagram of monochrome TV receiver.
4
4
Block diagram of monochrome TV receiver
40b.
Ans
What are uplink and downlink signals?
The signal transmitted from the earth to satellite is called uplink signal.
2
1
The signal transmitted from the satellite to earth is called downlink signal.
1
*******s*s********
Page 16