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Students can Download 2nd PUC Electronics Previous Year Question Paper March 2019, Karnataka 2nd PUC Electronics Question Bank with Answers helps you to revise the complete Karnataka State Board Syllabus and score more marks in your examinations.

Karnataka 2nd PUC Electronics Previous Year Question Paper March 2019

2nd PUC Electronics Previous Year Question Paper March 2019

Time : 3 hrs. 15 min.
Max Marks: 70

Instructions:

• The question has five Parts A, B, C and D.
• Part – A has no choice
• Part – D has two parts. Part -1 is from problems, Part – II is of essay type questions.
• Circuit diagram/timing diagram/truth tables are drawn wherever necessary.
• Problems without necessary formula/formulae carry no marks.

Part – A

Answer all questions: 10 x 1 = 10

Question 1.
Name the charge carriers in N-channel JFET.
Answer:
Electrons.

Question 2.
Write the value of bandwidth of an ideal OPAMP.
Answer:
Infinity.

Question 3.
Draw the waveform of damped oscillations.
Answer:

Question 4.
What is the function of transmitter in a radio communication system?
Answer:
Transmitter processes the information and transmits it.

Question 5.
Draw the waveform of AM wave when modulation index m_a=1
Answer:

Question 6.
Define fidelity in a radio receiver.
Answer:
Fidelity is the ability of the receiver to reproduce the input faithfully.

Question 7.
Mention one application of TWAC.
Answer:
TRIAC can be used in fan motor control.

Question 8.
Write the decimal equivalent of BCD code (00110101)₂.
Answer:
(00110101)₂ = 35₁₀.

Question 9.
Name anyone arithmetic operator in C-language.
Answer:
Addition or Subtraction.

Question 10.
Expand RADAR. or = r v                                                                       ‘
Answer:
RADAR – Radio Detection And Ranging.

Part – B

Answer any Five question.

Question 11.
Mention the steps to obtain DC-equivalent circuit of a CE amplifier.
Answer:

• Reduce all ac sources to ground.
• Open all the capacitors.

Question 12.
Calculate the gain of a negative feedback amplifier with an internal gain, A = 100 and feedback factor β= 1/10.
Answer:
A= 100, β = 1/10.

Question 13.
Write any two applications of crystal oscillator.
Answer:

• Digital watches.
• Clock, Calculators.
• Transmitters and Receiver.

Question 14.
Realise XOR gate using basic logic gates.
Answer:

Question 15.
Write the difference between combinational and sequential logic circuits.
Answer:

Combinational Logic Circuit	Sequential Logic Circuit
(i)  It does not have memory (ii)  Its output depends only on present input.	(i) It has memory. (ii) Its output depends on present and past input

Question 16.
Write any two instruction set of 8051 microcontroller.
Answer:
These instructions move the content of one register to another one. Data can also be transferred to stack with the help of PUSH and POP instructions.

Question 17.
Mention any two features of C-language.
Answer:
C is a powerful, flexible language that has gained worldwide acceptance in recent years. C is concise, yet powerful in its scope. It is a high-level language that also incorporates features of low-level languages. It is becoming the standard for program development on small machines and microcomputers.

It is possible to apply C to nearly all application areas. Modularity {process of dividing problems into sub-problems) makes C ideal for projects involving several programmers. C permits nearly every programming technique. C is widely available for most brands and type of computers. It is portable. With all the features C is not a difficult language, it is one of the easiest languages to learn and implement.

C programming can be used to write any complex program because of its rich set of built-in functions and operations. C compiler combines the capabilities of an assembly language with the feature of high-level language and therefore it is very much suited for uniting both system software and business packages. Because of its variety of data types, powerful operator programs in C are efficient and fast. C has the ability to extend, it means user-defined functions can also be added to C library.

Question 18.
Briefly explain the internet.
Answer:

1. Using internet, access to required information is easy, economical, reliable and fast.
2. With E-mail, messages reach destination with in minutes.
3. E-mail can be sent and received from any place.
4. Using E-mail, message can be sent to several persons simultaneously.

Part – C

Answer any five questions.   5 x 3 = 15

Question 19.
Compare the FET and BJT.
Answer:

FET	BJT.
1. It is unipolar device.	1. It is a bipolar device.
2. It is a voltage controlled device.	2. It is a current controlled devices.
3. Its input resistance is very high.	3. Input resistance is very low.
4. Current conduction is only by majority charge carriers either hole or electron.	4. Current conduction is both by electrons and holes.
5. It has high switching speed.	5. It has low switching speed.
6. Less noisy	6. More noisy.
7. Fabrication is easier in IC.	7. Difficult to fabricate in IC.

Question 20.
What is transistor biasing? Briefly explain the need for biasing a transistor
Answer:
The application of suitable DC voltage across the transistor terminals is called biasing of the transistor.

The reasons for biasing of a transistor are:

1. To make the operating point to be at the centre of the load line.
2. To make the collector current independent of temperature variations.
3. To maintain the operating point constant even though transistor is replaced by another of same type.

Question 21.
With a block diagram derive an expression for output impedance of aN amplifer with negative feedback.
Answer:

An amplifier should have a low output impedance so that it can deliver power to load without much loss. With negative feedback, the output impedance of the amplifier decreases which is desirable.

Let Z_o be output impedance of basic amplifier and Z_of be the output impedance with negative feedback. A hypothetical source of voltage V_o is applied at the output. By applying KVL to the output loop,

V_o = I_oZ_o +AV_i.
With negative feedback, input to basic amplifier with negative feedback is
V_i = V_s – V_f
V_i  = o – V_f
V_i  – V_f
{As input is short circuited, V = o}

As 1+Aβ>1, output impedance of amplifier decreases by a factor(1+Aβ)

Question 22.
Explain the importance of ionosphere in the radio communication.
Answer:
Ultraviolet radiation from the sun cause the upper atmosphere to ionize i.e. to become electrically charged. Hence a thick layer of ions formed at heights of 50 km to 400km. The ionosphere supports MF and HF wave propagation.
Its three layers are:

D layer: It is at a height of 70 km and has an average thickness of 10 km. It disappears in the night time. It reflects VLF and LF waves and absorbs MF and HF waves.

E layer: It is at a height of 100 km with a thickness of 25 km. This layer disappears at night. It helps in MF and HF wave propagation.

F layer: It is at a height of 150 km and extends upto 400 km. This layer exists during both day and night time. During day time, it splits into two layers F, and F₂, and combines to form a single F layer during night time.

F2 region. 250-400 km.

F1 region. 160-250 km.

E region. 95-130 km

D region. 50-95 km.

Troposphere Earth.

Question 23.
Derive an expression for the total power of AM wave.
Answer:
The total power in AM wave is equal to the sum of powers of the carrier, the upper sideband and the lower sideband.

Question 24.
In a SCR full wave rectifier the firing angle is 90°, rms voltage of an input to the rectifier is 230 V and the load resistance is 25Ω. Calculate V_dc and I_dc
Answer:

Question 25.
With a neat circuit diagram explain the working of power diode under forward bias condition.
Answer:

Question 26.
With a neat block diagram explain the satellite Transponder.
Answer:

Part – D

Answer any Three question  3 x 5 = 15

Question 27.
Calculate voltage gain (A_y) and input impedence (Z_in) of a given CE amplifer with values
\(r_{ e }=\frac { 26{ mV } }{ { I }_{ { E } } } ,{ V }_{ { BE } }=0.7V\) β = 100.

Answer:

Question 28.
Calculate the output voltage (V₀) for a given circuit below

Answer:

Question 29.
A transistor Colpitts oscillator has L = 4 mH, C₁ = 10 nF and C₂ = 10 nF. Calculate the frequency of oscillations.
Answer:

Question 30.
The current of a AM transmitter is 8A when the carrier is sent, it increases to 8.65 A when the carrier is modulated. Find the percentage of modulation. Also calculate the antenna current when the depth of modulation is 0.75.
Answer:

Question 31.
Simplify the Boolean expression using K-map. Y(ABCD) = Σm(0, 2, 4, 5, 8, 10, 12, 14) + Σd(6, 13)  Write the logic circuit for the simplified expression.
Answer:

Part – E

Answer any Four questions.

Question 32.
Compare CE, CB and CC amplifiers.
Answer:

Parameter	Types of Amplifiers.
	CE	CB	CC
Current gain	High (P)	Less than 1	Highest (1+ p)
Voltage gain	High	Moderate	Low
Power gain	Highest	Moderate	Moderate
Phase shift	180°	0°	0-
Input impedance	Moderate	Low	High
Output impedance	Moderate	High	Low
Bandwidth	Narrow	Wide	Wide
Applications	Used as AF amplifies	Used as RF amplifies	impedance matching

Question 33.
(a) What are active filters? (1 + 4)
Answer:
An active filter is a type of analog circuit implementing an electronic filter using active components, typically an amplifier. Amplifiers included in a filter design can be used to improve the cost, performance and predictability of a filter.

(b) With a neat circuit diagram explain the working of first order low pass active filter and draw its frequency response curve.
Answer:
Filter are circuits used to select a band of frequencies. The two types of filters are

• low pass filter and
• high pass filter.

Cut off frequency \(\mathrm{f}_{C}=\frac{1}{2 \Pi \mathrm{R}_{1} \mathrm{C}_{1}}\)
Frequency response of low pass filter.

Question 34.
Draw a block diagram and explain the different stages of FM transmitter.

Answer:
The modulating signal is applied to the pre-emphasis circuit, which improves signal to noise ratio, AF amplifier amplifies output of pre-emphasis. The processed signal is fed to reactance modulator. The reactance modulator uses a transistor or FET connected across tank circuit of carrier oscillator.

The oscillator frequency depends on the tank reactance which in turn depends on the instantaneous amplitude of modulating signal. Thus, output of reactance modulator will be a frequency modulated wave.

The oscillator is followed by a buffer amplifier which isolates oscillator from subsequent stages. The limiter maintains the amplitude constant. Class C power amplifier amplifies modulated wave to required power levels. The FM signal is then fed to the transmitting antenna.

Question 35.
(a)What is flip-flop?
Answer:
A flip flop is an electronic circuit with two stable states that can be used to store binary data. Flip-flops and latches are fundamental building blocks of digital electronics systems used in computers, communications, and many other types of systems. Flip-flops and latches are used as data storage elements

(b) With a logic diagram and truth table, explain the working of SR flip-flop, (1+4)
Answer:

Question 36.
Write a flow chart and explain the steps used in creating assembly language program in 8051 microcontroller
Answer:

Question 37.
Write a C-program to find largest among three numbers.
Answer:

Output:
Enter the three numbers 15
24
48
48 is largest number among 15,24 and 48

Students can Download 2nd PUC Electronics Previous Year Question Paper March 2017, Karnataka 2nd PUC Electronics Question Bank with Answers helps you to revise the complete Karnataka State Board Syllabus and score more marks in your examinations.

Karnataka 2nd PUC Electronics Previous Year Question Paper March 2017

2nd PUC Electronics Previous Year Question Paper March 2017

Time : 3 hrs. 15 min.
Max Marks: 70

Instructions:

• The question has five Parts A, B, C and D.
• Part – A has no choice
• Part – D has two parts. Part -1 is from problems, Part – II is of essay type questions.
• Circuit diagram/timing diagram/truth tables are drawn wherever necessary.
• Problems without necessary formula/formulae carry no marks.

Part – A

Answer all questions: 10 x 1 = 10

Question 1.
Write the function of source in JFET.
Answer:
Source supplies charge carriers for current conduction.

Question 2.
Name the power amplifier in which conduction angle is 360°.
Answer:
Class A.

Question 3.
Define slew rate.
Answer:
Slew rate is the rate of change of output.

Question 4.
What is the frequency of modulating signal if the bandwidth of AM wave is 10 KHz?
Answer:
\(f_{\mathrm{m}}=\frac{\mathrm{BW}}{2}=\frac{10 \mathrm{KHz}}{2}=5 \mathrm{KHz}\)

Question 5.
Define demodulation.
Answer:
Demodulation is the process of recovering original modulating signal from the modulated wave.

Question 6.
Draw the circuit symbol of IGBT.
Answer:

Question 7.
What is a counter?
Answer:
Counter is a logic circuit for counting the pulses.

Question 8.
Convert (1101)2 into gray code.
Answer:
(1011)_G

Question 9.
How many interrupt sources are there in 8051 microcontroller?
Answer:
6 including RESET or 5 excluding RESET.

Question 10.
Write C equivalent expression for the mathematical expression \(\sqrt{a^{2}+b^{2}}\)
Answer:
sqrt (a*a+ b*b)

Part – B

Answer any five questions.

Question 11.
Write any two differences between FET and BJT.
Answer:

S.No.	BJT	JFET
1.	It is a bipolar device.	It is a unipolar device.
2.	It is a current controlled device.	It is a voltage controlled device.
3.	Current conduction is by both holes and electrons.	Current conduction is by holes or electrons.
4.	Input resistance is low.	Input resistance is very high. (MCI)
5.	BJT is more noisy.	JFET is less noisy.
6.	Switching speed is less.	Switching speed is high.
7.	Fabrication in IC is difficult.	Fabrication in IC is simpler.

Question 12.
Mention the steps involved to obtain DC equivalent circuit of an amplifier.
Answer:

• Reduce all the AC source to zero.
• open all the capacitors.

Question 13.
Distinguish between positive feedback and negative feedback.
Answer:

• Positive feedback is the process of applying a portion of output in phase with the input.
• Negative feedback is the process of applying a portion of output out of phase with the input.

Question 14.
Write any two advantages of RC oscillators over LC oscillators.
Answer:

• RC oscillators provide constant output and good stability.
• RC oscillators do not require any inductor and hence size and cost get reduced.

Question 15.
Write Shockley’s diode equation for current through the power diode and explain its terminology.
Answer:
\(I=I_{ s }\left( e^{ \frac { qv }{ KT } }-1 \right)\)

• I_s = Reverse saturation current
  
• T = Absolute temperature
  
• K = Boltzmann constant
• q = charge of electron
• V = voltage across diode.

Question 16.
Determine average value of DC from chopper. Given T= 2 ms, T_QN= 0.5 ms and supply voltage is 24V.
Answer:
Duty ratio = \( \frac{T_{o N}}{T}=\frac{0.5}{2}=0.25\)
V_dc = Duty ratio x V_s = 0.25 x 24 = 6V.

Question 17.
Realise NOT and OR-gate using NOR-gate
Answer:

Question 18.
Distinguish between uplink and downlink signals
Answer:

Uplink	Downlink
1)  Signal transmitted from ground station to satellite 2) Frequency range is 6 GHz	1) Signal transmitted from satellite to ground station. 2) Frequency range is 4 GHz.

Part – C

Answer any five questions.  5 x 3 = 15

Question 19.
What is a DC load line? Mention any two advantages of voltage divider bias.
Answer:
Operating point is the zero signal values of collector I_c and collector to emitter voltage V_CE of a transistor. DC load line is a straight line drawn on the output characteristics representing output DC voltage and corresponding direct current under no signal conditions.

The operating point does not depend upon the value of β of the transistor. Hence the operating point does not change its position due to rise in temperature or replacing a transistor of different p value. Hence voltage divider bias provides excellent stabilisation and is preferred to other biasing methods.

Question 20.
Calculate the input impedance of a negative feedback amplifier if input impedance without feedback is 10 KQ. Given A = 100 and β = 0.01.
Answer:
Z_if = Z_i(1 +Aβ)
= 10 x 10³ (1 + 100 x 0.01)
= 20 x 10³ Ω
= 20kΩ

Question 21.
With block diagram, explain basic communication system.
Answer:

Question 22.
Draw the equivalent circuit of transmission lines for low frequency. Mention any two types of antennas.
Answer:

Types of Antenna:

• Helical antenna
• Yagi antenna
• Loop antenna

Question 23.
Write the circuit diagram, input and output waveforms of SCR halfwave rectifier with RC triggering circuit.
Answer:

The SCR is connected with a diode bridge rectifier. The rectifier circuit converts AC to a unidirectional current through the thyristor. The voltage on the capacitor follows the diode rectifier waveform because RC circuit is connected to diode rectifier. During each half cycle when the voltage across the capacitor reaches trigger level which is just enough to supply gate trigger current to thyristor, then thyristor starts conducting. Firing angle \(\alpha=\left(\frac{x}{\mathrm{y}}\right)_{180}\)

Question 24.
Draw the labelled block diagram of microcontroller.
Answer:

Question 25.
How do you represent.
(i) logical AND
(ii) logical OR
(iii) logical NOT operators in C programming?
Answer:
Internet is worldwide interconnection of millions of computers by means of complex network which serves as an inexpensive communication medium.

1. Long-distance telephone and cable TV systems.
2. To provide LAN connections.
3. Closed-circuit TV systems used for security.
4. Aircraft communication and controls.

Question 26.
What is internet? Write few applications of fibre optic communication system.
Answer:
Internet

1. Using internet, access to required information is easy, economical, reliable and fast.
2. With E-mail, messages reach destination with in minutes.
3. E-mail can be sent and received from any place.
4. Using E-mail, message can be sent to several persons simultaneously.

Applications

1. Long-distance telephone and cable TV systems.
2. To provide LAN connections.
3. Closed-circuit TV systems used for security.
4. Aircraft communication and controls.

Part – D

Answer any Three questions:   3 x 5 = 15

Question 27.
For the given CE amplifier circuit using silicon transistor. Calculate
i) Voltage across R₂
ii) I_E
iii) Z_in(base)
iv) Z_in (and)
v) Z_o
Given \(\text { Given } r^{\prime} e=\frac{26 m V}{I_{E}}\) and β = 100

Answer:

Z_in = R₁ || R₂|| Z_in(base) =1.38kΩ = 2kΩ
Z_b =Rc || R_L =(10kΩ) || (10kΩ) = 5kΩ

Question 28.
Calculate the output voltage if V₁= 300mV and V₂ = 700 mV in the following circuit.

Answer:

Question 29.
A Hortley oscillator oscillates at 15 KHz. If the capacitor in the tank circuit has a value of 0.01 pF and one of the inductors value is 1 mH, calculate the value of the other inductor.
Answer:

L₁ + L₂ = L_T= 11.25 mH
L,₁+ 1mH= 11.25mH, L₁ = 10.25mH

Question 30.
A frequency modulated signal is given by 10sin[6 x 108t + 5 sin 1250t].
Determine
i) Carrier frequency
ii) Modulating frequency
iii) Modulation index
iv) Maximum deviation
v) Carrier swing
Answer:

Maximum frequency deviation = δ= m_f f_m. = 5 x 199.04= 995.2 Hz
Carrier swing = 28 = 2(995.2) = 1990.4 Hz.

Question 31.
Simplify the Boolean expression Y = sm(l,2,3,8,9,11,13) + sd(0,10,15) using K-map. Draw the logic diagram using NAND-gates to realise the simplified expression.
Answer:

Part – E

Answer any Four questions.  4 x 5 = 20

Question 32.
Give the comparison between CB, CC and CE amplifiers on the performance characteristics.
Answer:

Parameter	Types of Amplifiers.
	CE	CB	CC
Current gain	High (P)	Less than 1	Highest (1+ p)
Voltage gain	High	Moderate	Low
Power gain	Highest	Moderate	Moderate
Phase shift	180°	0°	0-
Input impedance	Moderate	Low	High
Output impedance	Moderate	High	Low
Bandwidth	Narrow	Wide	Wide
Applications	Used as AF amplifies	Used as RF amplifies	impedance matching

Question 33.
What is a logarithmic amplifier? With circuit diagram, obtain an expression for output voltage of logarithmic amplifier using OP-amp.
Answer:
Answer:


∴ The output voltage is proportional to natural logarithm of input voltage.

Question 34.
With a labelled block diagram, explain the working of AM transmitter.

Answer:
The transmitter performs modulation and raises the power level of a modulated wave to required level for effective radiation.

The microphone converts the audio signal into an equivalent audio electrical signal. The output is filtered to have a bandwidth of 10kHz.

The pre amplifier provides the required voltage amplification. The driver amplifier increases the power level of the signal as required by the high power modulation amplifier.

The high frequency carrier wave is generated by a crystal oscillator which has highest frequency stability. The Carrier signal is fed to a buffer amplifer which is a low gain, high input impedance amplifer which isolates crystal oscillator and the power level of the carrier signal to drive the modulated class C amplifier.

The modulating audio signal and carrier signal are applied to the modulator. The collector modulation is used for modulation in high power transmitter. The transmitting antenna transmits the signal.

Question 35.
Explain with circuit diagram and truth table, the working of clocked SR flip flop using NAND gates.
Answer:

It is constructed using inverters inserted into inputs of cross coupled NAND gates.
Working:

1. When S=0, R=0, it does not respond and hence outputs Q and Q will remain in their previous state. This is called HOLD condition.
2. When S=1 and R=0, the output Q and Q change to 1 and 0. This condition is called SET state.
3. When S=0, R=1, the output Q and Q change to 0 and 1. This condition is called RESET state.
4. When S=1 and R=l, it drives output Q and Q both to HIGH which is FORBIDDEN or INVALID condition.

Question 36.
Write an assembly language instructions to move 45H into register A and 5 EH into register R₀. Then add them together and save the result in R_t. What is the content of R, after the execution of the program.
Answer:

Question 37.
Write a C program to accept three integer and find their sum and average. Find the sum and average of 5, 6 and 7.
Answer: