CHAPTER 1

INTRODUCTION TO ELECTRONICSOne marks questions

1. Who discovered electron?Ans: J.J Thomson

2. What is internet?Ans: Internet is the largest and the most effective communication platform.

3. Expand MOSFET.Ans: Metal Oxide Semiconductor Field Effect Transistor.

4. Expand IGBT.Ans: Insulated gate bipolar transistor.

5. Expand VLSI.Ans: Very large scale integration

6. What is a microcontroller?Ans: A microcontroller is a computer on chip because it has CPU, memory, input and output pins, timer and clock circuit, all built on a single silicon chip.

7. Expand EPRAM.Ans: Erasable Programmable read only memory.

Two marks questions 1. Mention few applications of electronics.

Ans: 1.Entertainment. 2. Communication 3 Defence application 4. Industrial applications 5. Medical applications.

2. List the household electronic equipmentAns: TV, DVD player, Microwave oven, Digital camera.

3. Write a note on role of electronics in medical scienceAns: Electronic devices are widely used in medical science in the diagnosis and treatment of different devices. The electronic devices commonly used in the field of medical science are Electrocardiographs (ECG), X-rays, ultrasound scanning machines, endoscopy, glucometer.

4. Discuss the application of electronics in defence.Ans: In defence, Radar, Sonar and infrared systems are used to detect and locate warships, jet fighters and submarines. Missiles controlled by electronic signals can target enemies very accurately over long distances. Electronic security systems are used across the border to guard the country.

Chapter 2

PRINCIPLES OF ELECTROICITY, NETWORK THEOREMS AND AC PRINCIPLES

One marks questions

1. What is the unit of electric charge?Ans: Coulomb.

2. What is the magnitude of charge of electron?Ans: 1.6×10-19C

3. Define electric current Ans: Electric current is defined as the rate of flow of charge through a cross section of a conductor.

4. Define ampereAns: The current flowing in a conductor is said to be one ampere if one coulomb of charge flows through the conductor in one second

5. State ohms law.Ans: Ohms law states that current flowing through a conductor is directly proportional to the potential difference across the conductor, when the temperature and other physical conditions of the conductor are maintained constant.

6. What is a node?Ans: Node is a point in a circuit where more than three resistors meet.

7. Write an expression for instantaneous value of AC Voltage Ans: Instantaneous voltage v=V sin ωt.

Two marks questions 1. Manton any two properties of charges

Ans: i). Like charges repel, unlike charges attract. ii). charges always reside on the outer surface of a conductor only

2. Mention limitations of Ohm’s law.Ans: i). Ohm’s law is not valid when the physical conditions of the conductor change. ii). Ohm’s law is not valid at very low and very high temperature

3. Define peak value and rms value of ac.Ans: Peak or maximum value of ac is the maximum voltage or current attained by AC in the half cycle.

4. Define (i) average value (ii) time period of ac.Ans: i). Average or mean value of ac is average of instaneous voltages of ac taken over one half cycle. ii). Time period of ac is time taken to complete one AC cycle?

5. How many electrons are be removed from a body to charge it to 16nC?Ans:

electrons 6. What are the resistances offerd by (i) short circuit (ii) Open circuit.

Ans: (i) Zero (ii) Infinity

Three marks qustions 1. State Kirchhoffs laws

Ans: i). The sum of the currents flowing a node in a circuit is equal to sum of the currents away form the node. ii). the algebraic sum of emfs in any closed loop of a network is equal to the algebraic sum of IR drops in that loop.

2. What is a voltage source? How is it converted into a current source?Ans: Voltage source is that which supplies electrical energy to the circuit in the form of voltage.

3. What is a current source? How is it converted into a voltage source?Ans: Current source is that which supplies electrical energy to the circuit in the form of current.

4. What are ideal coltage and current soures? Draw the 1-V characteristics of practical voltage source.Ans: Ideal voltage source is the one that supplies constant coltage to the load irrespective of changes in the load resistance. It has zero resistance. Ideal current source is that which supplies constant current to the load irrespective of changes in the load. It has infinite resistance

5. For the AC waveform given below, find (i) Vrms (ii) Vp (iii) Vavg (IV) frequency.

Five marks questions

1. Derive an expression for the effective resistance of resistors connected in series.

Ans: consider two resistors R1 and R2 connected in series to a cell of emf E. In series combination the resistor are connected end to end and same current flows through each of them.

The emf of the cell equals voltage drops across each of the resistors

E=V1 + V2 = IR1 + IR2 From ohms law

E = I (R1 + R2) →(1)

Effective or equivalent resistor is a single resistor which has the same effect as combination of resistors. If Rs. is the effective resistance, E = IRs – (2)

From the equations (1) and (2),

Rs = R1 + R2

Effective resistance of resistors in series in sum of the individual resistances

2. Derive an expression for effective resistance of resistors connected in parallel.

Ans: Consider two resistors R1 and R2 connected in parallel between the same two common points. In parallel combination, voltage across each resistor is the same.

Let I1 and I2 be the currents through the resistors R1 and R2

The current from the cell equals sum of the currents through the two resistors, i.e.,

Equivalent or effective resistor Rp is a single resistor which has the same effect as tlle parallel

combinations. If Rp is the effective resistor, then I= VRp → (2)

From equations (1) and (2)

Hence, reciprocal of effective resistance of number of resistors is parallel is sum of the reciprocals of the individual resistances.

3. Stat and explain thevenin’s theorem with an example. Or Write procedure to thevenise a given circuit with an example Ans: Thevenin’s theorem states that any linear bilateral network having several voltage sources and resistors can be replaced by a simple circuit having one voltage source V thin series with one single resistor Rth.Step 1 : Identify and remove load resistor RL to convert circuit as a two terminal network.Mark the two terminals as A and B.Step 2 : To find VTh, calculate the open circuit voltage between terminals A and B

Step 3 : to find Rth replace all voltage sources in the network by their internal resistances and then find the effective resistance between terminals A and B

Step 4 : Construct Thevenins equivalent circuit having Vth in series with Rth hand reconnect the load resistor which was earlier removed.

4. State and explain applying superposition theorem to given circuit.Ans: In any linear bilateral network consisting of two or more independent sources, the resultant current or voltage in any branch is the algebraic sum of the currents or voltages caused by each independent sources acting alone, with all other independent sources are being replaced by their internal resistances. Procedure for using superposition theorem:

Step 1: Retain the source V1 and replace all other sources by their internal resistances.

Step 2: Current in various branches and their voltage drops due to V1 alone are determined as follows.

Step 3: Consider V2 alone and find the currents and voltages as follows

Step 4: Find the algebraic sum of currents and voltage drops in a branch.

5. Find the load current and load voltages applying thevenin’s theorem.

To find RTh

6. Find the current through 4Ω resistor using superposition theorem.

Chapter 3MEASURING INSTRUMENTS

One mark questions1. What is meant by measurement ?

Ans : Measurement is the process of comparing a given quantity with a standard unit 2. Which is BP measuring instrument?

Ans: Sphygmomanometer 3. What is an ultrasound scan?

Ans: Ultrasound scan (i) Helps to monitor growth of unborn child and check abnormalities.

(ii) Detect abnormalities of heart valves.(iii) detect abnormal widening of blood vessels.

4. What is a pulse oximeter?Ans: It is a device which can detect saturation level of haemoglobin in arterial blood

Two Marks Questions

1. Write any two applications of an oscilloscope Ans: 1. It is used to measure AC/DC voltage. 2. It is used to measure time period and frequency of AC

Chapter 4

PASSIVE ELECTRONIC COMPONENTSOne Marks Questions

1. Give any one example for the active component Ans: Transistor

2. Define temperature coefficient of resistance of a material Ans: Temperature co-efficient of resistance is defined as the ratio of increase in resistance per 0C rise in temperature to its resistance at 0oC

3. Define resistivity or specific resistance of a material Ans: Resistivity of the material is defined as the resistance of a conductor of unit length having unit area of cross section.

4. What does the fifth band of a 5 band colour coded resistor indicate?Ans: tolerance

5. Draw the circuit symbol of preset

Ans:6. Write an expression for energy stored in a capacitor

Ans:7. Write an expression for capacitance of a parallel plate capacitor

Ans:

8. What is the principle of transformer?Ans: Mutual induction

9. Write the relation between turns ratio, voltage ratio and current ratio in a transformer

Ans:10. Draw the symbol of LDR?

Ans:

Two marks Questions

1. Mention the factors on which the capacitance of a capacitor depends Ans: Capacitance of a capacitor depends on (1) area of plates of capacitor. (2) distance between two plates (3) dielectric constant of the material between the two plates.

2. List the factors on which self-inductance of a coil depends.Ans: Self-inductance of a coil depends on (a) Number of turns in the coil (b) relative permeability of the coil(c) length of the coil (d) cross-sectional area of the

3. Mention different types of a transformersAns: (a) Power transformer (b) Audio frequency transformer (c) Radio frequency transformer (d) intermediate frequency transformer

4. what is a capacitor? Mention S.I. unit of capacitance

Ans: Capacitor is a device which is used to store charges. S.I. unit of capacitance is farad (F)

5. Write the applications of chokes and relays.Ans: Chokes are used in

(A) tube light sets (B) in radio and TV receivers (B) in power supplies (D) in RF running circuits

Relays are used 1) as protective device 2) to realise logic functions 3) as counters 4) as automatic switching device to operate street lights, UPS, buzzers

6. Find the resistance values of resistors with following colour bands.

Three marks Questions 1. Explain the principle of a capacitor

Consider two metal plates M and N separated by asmall distance. Let inner surface of metal plate M be positively charged. Then due to electrostatic induction, an equal and opposite negative charge is induced on the inner surface of plateN. The negative charge on N tries to decrease the potential on M and positive charge onN tries to increase the potential on M. as

the negative charges on plateN are nearer to plate M, it has greater effect on plateN. Hence, there is net decrease in potential on M and thus the capacitance of the capacitor increases.

it the outer surface of plateN is grounded (or connected to earth), the charges on the outersurface of plate N are neutralised. Due to negative charges only on the plate N, the potential of plate M is greatly reduced. Hence the capacitance of plate M increases. When

grounded conductor is placed near a charged conductor with a dielectric medium in between, the capacitance of the system increases.

Capacitance of the capacitor cab be increased by

1. reducing the distance between the plates.

2. placing the medium of high dielectric constant between the plates of the capacitor.

2. Derive an expression for the equivalent capacitance of two capacitors connected in series.

Ans

Inseries combination, the capacitors are connected end to end. The charge on each capacitors is the same and emf of the cell equals the sum of voltages across the three resistors

Consider three capacitors C1,C2, C3 connected in series.

Let the combination be replaced by an equivalent capacitor CS which has the same effect as the combinations of capacitors. If CS is the effective capacitance.

The reciprocal of effective capacitance of capacitors in series is the sum of reciprocals of individual capacitances.

3. Derive an expression for the effective capacitacne of capacitors connected in parallel.

Ans: capacitors are said to be in parallel if they are connected between the same common points. The voltage across each capoacitor in parallel is the same

let C1, C2 and C3 be the capacitors connected in parallel.

let V be the applied voltage across the combination.

the charge Q from the cell equals the sum of voltages across the capacitors

Equivalent of effective capacitor is a single capacitor which has the same effect as the combinations of capacitors.

if CP is the effective capacitance then

hence, when capacitors are connected in series, the effective capacitance is the sum of indicidual capacitances.

4. explain the construction and working of loud speaker.

Ans: A loud speaker is a transducer that changes electrical energy into sound waves of varying

pressure.

Voice coil is suspended in the strong magnetic field of a circular permanent magnet. The permanent magnet of a speaker provides a steady magnetic field. the two leads of voice coil are connected with write to terminals on the speaker fame.

When audio signal current flows through voice coil, it produces varying magnetic field in the coil. the varying magnetic field moves the voice coil in and out in accordance with variations in the relectrical audio signals hence the diaphragm attached to voice coil vibrates due to which compressions and rarfactions are formed and the sound waves are produced.

Chapter 5

APPLICATION OF DC AND AC TO PASSIVE COMPONENTS

one marks questions

1. What is transient period?

Ans: Transient period is the time period during which current and coltage changes before steady state is reached when dc is applied to RC and Rl circuit.

2. Write the expressions for the (1) Voltage across capacitor during charging and (2) voltage across capacitor during dischargeg

3. define time constant of RL circuit.

Ans: time constant of RL circuit is the time taken by the current to grow to 63.2% of the maxmum value.

4. Write the expression for resonance frequency of a series resonance circuit.

5. Define bandwidth

Ans: bandwidth is the difference between the two frequency points on either side of the resonant frequency where the current rises to 70.7% of ots maximum value.

6. Define quality factor.

Ans: The quality factor of a circuit is the ratio of resonant frequency to the bandwidth.

Two marks Questions

1. Draw the graph showing voltage across the capacitor during charging.

Ans

Five marks questions

1. Discuss the charging of a capacitor in a RC circuit.

ans

Consider a resistor R and a capacitor C connected in series with battery of emf E. when swith is in position A, the capacitor C gets charged through R exponentially with time. hence voltage across the capacitor increases exponentially and the current in the cricuit decreases exponentially. when the

capacitor is fully charged, the current becomes Zero. the instantaneous value of Voltage across the capacitor during charging is given by

2. Discuss the growth of current in RL circuit.

ans

3. Describe the phenomenon of resonance on a series resonant circuit.

Ans: Consider an AC circuit consisting of an inductance (L), capacitor C and a resistance R connected in series to an AC source. Let the instantaneous voltage of ac source be

Let VL VR VC be the voltages across the inductor, Resistor and capacitor.

4. explain low pass filter with its frequency response.

Ans: Low pass filter passes all the low frequencies below a cutoff frequency and stops or attenuates the higher frequencies.

appears across the output. At high freqnencies, the capacitor offers very low reactance and

acts as a short circuit and hence output becomes Zero. the cut off frequency

Chapter 6.

SEMICONDUCTORS, DIODES AND APPLICATIONS OF DIODES

one marks Questions

1. what is forbidden energy gap?

Ans: The gap between conduction band and calence band in the energy band diagram is known as forbidden energy gap

2. name majority charge carriers in n. type semiconductor.

Ans: Electrons.

3. what is depletion region?

Ans: Depletion region is the region near the p-n junction where mobile charge carriers namely electrons and holes are depleted or emptied.

4. In which type of biasing is the p-n junction diode resistance high?

Ans: In the recerse biasing of the p-njunction.

5. Mention the diode equation.

Ans: Shockleys equation of diode equation is

6. what is an ideal diode?

Ans: An ideal diode is a device is a device which offers zero resistance (perfect conductor) when forward biased and offers infinite resistance when it is reverse biased .

7. what is meant by rectification?

Ans: rectification is the process of converting AC voltage into a pulsating DC voltage

8. Name the component used to construct adjustable voltage regulator?

Ans: ICLM317.

9. Draw the symbol of schottky diode.

ans

Two marks Questions

1. Difine ripple factor and give its significance.

Ans: Ripple factor is the ratio of rms value of AC component of the load voltage to the average DC value of load voltage.

Smaller the value of ripple factor, greater is the DC component in the output and hence better is the rectifier.

2. How many diodes are used in a (i) center tapped fullwave rectifier and (ii) bridge rectifier.

Ans: (i) centre tapped fllwave rectifier requires two diodes.

(ii) Bridge rectifier requires four diodes.

3. what is the maximum efficiency of a fullwave rectifier and halfwave rectifier?

Ans: Efficiency of full wave rectifier is 81.2% and efficiency of halfwave rectifier is 40.6% .

Three marks Questions

1. Define ideal diode. Draw its V-I characteristics.

Ans: an ideal diode is a device which offers zero resistance when forward biased and offers infinite resistance when reverse biased.

2. what is zener breakdown? Draw V-1 characteristics of zener diode.

Ans: when heavily doped diode which has narrow depletion region is subjected to a reverse voltage the high electric field at the junction breaks covalent bonds. hence large number of electron holes are produced and the diode is saide to be under zener breakdown.

3. Explain second approximation of zener diode.

Ans: In second approximation treats the diode as a switch in series with a battery of potential VB

4. What is a bleeder resistor? Mention its uses.

Ans: Bleeder resistor is a resistor connected across filter output so as to maintain minimum current throughthe choke at all time.

It is also used to

(I) improve voltage regulation of power supply

(II) provide a path for the filter capacitor to discharge so as to avoid possibility of electric shock to techincians.

5. what is a varactor diode? Drae its symbol and mention any two of its applications

Ans: Varactor diode is a diode which acts as a variable capacitor under reverse biased condition

they are used in LC tuned circuits, TV receviers, FM recevers.

6. Draw the equivalent circuits for (i) reverse biased ideal diode (ii) second approximation diode and (iii) third approximation diode.

ans

Five Marks Questions

1. Classify solids based on energy band diagram.

ans

Conductors: These are materials which allow the current to flow through them easily. In conductors, the valence band and conduction band overlap comletely due to which the valence electrons dirft to conduction band easily. Even at room temperature, there are large number of free electrons. Hence due to small voltage applied, a large current flows through them

Semicomductors : These are the materials with electrical conductivity lying between those of conductors and insulators. The forbidden energy gap between valence band and conduction band is

0.7 ev for gremanium and 1.1 eV for silicon. at absolute zero, a semiconductor acts as an insulator. as the temperature increases, more valence electroms jump to comduction band. hence the conductivity of semiconductors increases with rncrease in their temperature.

Inslutors: Insulators are the materials that do not allow the electirc current to flow through them easily. the valence band is completely filled and conduction band is completely empty in insulators. the forbiddenenergy band between conduction band and valence band is nearly 5eV. In conduction band, there are no free electrons present at room temperature. Hence, the insulators do not conduct at all at room temprature.

2. Explain the working of pn junction when it is forward biased.

the diode is said to be forward biased if its p type material is connected to positive terminal of the battery and n type material is connected to negative terminal of the battery. the electrons in then type material are repelled towards pn junction by negative terminal of the battery and holes in p type material are repelled by positive terminal of the battery. this decreases the width of deplection layer and height of potential barrier. hence the more number of majority charge carriers diffuse across the junction and recombine with free electrons in the n region

for each recombination that takes place near the junction, a cavalent band in the p reginon neat the positive terminal breaks. the released free electron enters the positive terminal of battery and the hole moves towards the junction. For revery free electron that enters positive terminal of the battery, an electron moves form the negative terminal to the n region and move towards the junction. Hence anlarge currnet flows across the junction. Therefore. a forward biased pn junction offers very low resitance (few ohm)

3. Draw and explain the V-I characteristics of the diode.

Ans: The V-I characteristics of a diode is the graph between the voltage across the diode and the current folowing through it.

the V-I characteristics can be divided into two parts namely

1) Forward characteristics 2) Reverse characteristics.

1) Forward characteristics of semiconductior diode:

the circuit for plotting V-I characteristics of diode is as shown. the resistance R limits the current to a permissible value. Voltmeter measurses the voltage across the diode and millianmmeter reads the current flowing through the diode

the forward voltage VF is increased in steps of 0.1V and the corresponding forward current IF are noted. A graph of VF along x axis and corresponding IF along y axis given the forward characteristics curve.

Diode current IF is zero, when VF = 0 when VF is more than barrier potential, current IFincreases. the forwad voltge VF at which forward current starts to increase repidly is called the knee voltage or cut in voltage or threshold voltage (Vk) For gremamium diode,

Vk = 0.3 V and for silicon diode, Vk = 0.7V

Reverse characteristics of a pn junction:

4. Write a note on diode approximations.

Ans: Diode approximation is the convenient method used to represent a diode by a combination of ideal diode and linear circuit elements.

Depending on the circuit conditions, three approximations of diodes are used.

First approximations of ideal diode:

an ideal diode is a device which coaducts with zero resistance (prefect conductor or closed switch) when forward biased and offers infinite resistance (perfect insulator and open switch) when recerse biased.

5. Describe the working of fullwave centr tapped rectifier.

Ans: Full wave rectifier is a circuit that converts the entire AC input cycle into varying DC output

6. Explain the working of zener diode as a voltage regulator.

Ans: In a DC power supply, the output voltage should remain almost constant even as the input and load varies.

Voltages regulation is a measure of ability of a DC source to maintain a constant output voltage, even when there is variation in the laod resistance or input voltage

Zener diode as a voltage regulator

Zener diode can be used as a voltage regulator to provide a constant output voltage from a source whose voltage may vary.

the two types of voltage regulator are (i) line regulation (ii) load regulation

Load regulation:

the zener diode starts conducting only when the source voltage VS is greater than zener breakdown voltage VZ

when V s is increased form OV, load current IL increases with applied coltage. Current through zener diode will be zreo.

If VS is more than VZ the zener diode breaksdown and conducts. increasing the input voltage further increases voltage across the resistor RS and voltage across load VL remains constant at VZ

Line regulation:

For load regulation, Vs is made greater than Vz Vs is kept constant and load resistance RL is varied. If RL is decresed, current IL increases and IZ decreases by same value, but output voltage VL = Vz remains constant.

If RL is increased, IL decreases and IZ increases, but output voltage VL = Vz remains constant.

Chapter 7

BIPOLARJUNCTION TRANSISTORone marks questions

1. what is a transistor ?

Ans: Transistor is a three terminal semiconductor device with two pn junctions which can amplify weak electrical signal and it can also be used as a switch

2. Draw the symbols of (i) npn transistor and (ii) pup transistor

Ans:

3. Mention (i) heavily doped region (ii) lightly doped regions of a transistor.

Ans: (i) Emitter (ii) Base

4. write the relation between the current components of a transistor.

Ans: IE = IB + IC

5. in which mode of operation the transistor can used as an amplifier ?

Ans: Active mode

6. In which modes of operation the transistor can be used as a switch ?

Ans: Saturation (closed switch ) and cutoff (opn switch)

two marks Questions

1. Distiguish between

Ans: is the DC current gain which is the ratio collector current to emotter current in CB mode.

is the de current gain in CE mode which is the ratio of collection current to base current

2. What is a phototransistor? Draw its symbol.

Ans: A photo transistor is a three terminal optoelectronics device

3. What are saturation and cutoff region?

Ans: saturation region is the rgion of output characteristics between VCE = O and knee voltage cut off region is the region of the output charateristics below IB = O.

five marks Questions

1. Expain the working of an npn transistor.

ans

The emitter base junction is forward biased by power supply VEE and the collector base junction is reverse biased by the power supply VCC

The negative terminal of VEE repels the majority charge carriers electrons in the n type emitter towards the base region. when VEE is greater thaln the barrier potential of emitter base junction the electrons from emitter region move to the type base region. This forms the emitter current IE.

The base is thin and has only few electrons. Hence only few electrons and holes recombine and this forms the base current IE. the remaining free electrons in the base region move to collector region attracted by the +VCC. They move through the collector region into +VCC this forms collector current Ic.

The elaion connecting the currents in the transistoris IE =IB + IC.

2. Explain CE mode input and output characteristics of a npn transistor. Distinguish between the cutoff, active and saturation regions of a transistor.

Ans

The circuit to plot the CE characteristics of the transistor is as shown in the diagram.

The two types of characteristics are:

(1) Input characteristics (2) Output characteristics

Input Characteristics :

It gives the relationship between input voltage VBE and the input current IB when the output voltage VCE is kept constant. VBE is varied and corresponding IB values are noted keeping VCE constant. the input characteristics curve is similar to that of a forwaed biased semiconductor diode as emitter base junctioni s a pn junction

CE output characteristics

It is a graph of output collector Ic against output collector to emmitter voltage VCE for a cinstant input base current IB

From the graph, it is clear that the output current IC depends upon input current IB and VCE has no control over IC

Chapter 8

DIGITAL ELECTRONICSone marks questions

1. what is a nibble?

Ans: Nibble is group of foue bits

2. What is a byte?

Ans: Byte is a group of eight bits

3. Write 1’s complement of a binary number 11001.

Ans: 00110.

4. what is a logic gate ?

Ans: Logic gate is a digital circuit that makes logic decisions.

5. what types of gate is obtained when two switches are (i) in paralled (ii) in series?

Ans: (i) OR gate (ii) AND gate.

6. Draw the logic symbols of (i) NOT gate (ii) OR gate and (iii) AND gate?

Ans:

Two Marks Questions

1. Distingush between analog and digital signals.

Ans: Analog systems are syserms which are capable of processing a continuous range of values varying with respect to time.

Digital sysems are systems which process discrete values .

2. What is decimal equivalent of DAD16.

Ans:

3. Find the 2’s complement of the binary number 011111100002.

Ans

4. What are least significant bit and most significant bit?

Ans: The left most bit of a binary number which has highest place value is called most significant bit. the right most bit of a binary number which has the least place value is called least significant bit.

Three marks questions

1. Draw the two input diode OR gate and write its truth tables?

Ans:

2. Show that A+ AB = A+B.

Ans:

3. Simplify y

Ans:

4. Draw the circuit of DTL NOR gate and write its truth table.

Ans:

Five Marks Questions

1. Explain the transistor NOT gate

Ans:

Working:

Case (i) When input is LOW, base emitter junction has no forwaed bias applied and hence base and collector currents become zero. the transistor is driven to cut off and it acts as an open switch. Hence the output at the collector becomes HIGH.

Case (ii) When input is HIGH, base emitter juction is forward biased and hence base and collector currents flow driving the transistor to satuation. Hence output at the collector becomes LOW.

2. Explain the action of a two input diode AND gate.

Ans: AND gate is a logic gate which produces a HIGH output only when all its inputs are HIGH.

Working :

Case (i) When A=0, B=0, Both the diodes are forward biased and act like closed switches. Hence all the applied voltage drops across R1 and the output voltage becomes LOW.

Case (ii) When A=0, B=1, diode D1 conducts as it is forward biased and diods D2 does not conduct as it is reverse biased. Hence all the applied voltage drops across R1 and the optput voltage becomes LOW.

Case (iii) When A= 1, B=0, diode D1 does not conduct but D2 conducts being forwaed biased. Hence all the applied voltage drops across R1 and the output voltage at y becomes LOW.

Case (iv) When A=I, B=1 both diodes are reverse bised and do not conduct. No current floes through R and hence no voltage drop across R. Hence output at y becomes HIGH.

3. Explain the action of two input diode OR gate.

Ans: OR get is a logic circuit whose output is LOW only when all its inputs are LOW

Case (i) When A=0, Both the diodes are not conducting. no current flows through resistor RL and hence output y=0,

Case (ii) When A=0, B=1 D1 is reverse biased and does not conduct. D2 is forward biased and conducts. Hence current flows through RL making output y=1.

Case (iii) when A=1, B=0, D1conducts as it forward biased and D2 doesnot conduct as it is reverse biased. The current flows through RL and output y=I

Case (iv) when A=1, B=1, both the diodes conduct as they are forward biased. The current flows through RL making output y HIGH.

4. Expain the action of two input DTL NAND gate.

Ans:

Case (i) When both inputs A and Bare LOW (OV), both the diodes D1 and D2 are forwaed biased. Hence Voltage at junction P of the diode becomes zero. This makes the transistor Q to go to cut off. Hence the output at the collector of the transistor becomes HIGH.

Case (ii) When A is LOW and B is HIGH, D1 is forward biased and D2 is reverse biased hence the voltage at P becomes zero. This makes the trasistor to go to cut off state and therefore output at its collector becomes HIGH.

Case(iii) When A is HIGH and B is LOW, D1 is reverse biased and D2 is forward biased due to which voltage at pis zreo. This makes the transistor to go to cut off state and therefore output at its collector becomes HIGH.

Case(iv) When both the inputs are HIGH, D1 and D2 are reverse biased. Hence voltage at P becomes +VCC. this makes the transistor Q to go to saturation and transistor acts like a closed swich. Therefore output becomes LOW.

5. State and prove De Morgan’s theorems.

Ans: First theroem: the complement of a logical sum is equal to logical product of complements

.

Second theorem: the complement of a logical product is equal to the logical sum of complements.

.

Chapter 9

PRACTICAL ELECTRONIC COMPONENTS, THEIR SPECIFICATIONS

one marks questions

1. Name the type of capacitor having polarity.

Ans: Electrolytic capacitor.

2. Mention any one part number of a positive voltage regulaor

Ans: 78XX series voltage regulators are positive voltage regulators.

3. Mention any one part number of a negative voltage regulator.

Ans: 79XX series voltage regulators are negative voltage regulators.

Two marks Questions

1. what do you mean SIP and DIP package?

Ans: Single in-line package (SIP) has one row of connecting pins. Dual in line package (DIP) are packages with two rows of leads on two sides of the package.

2. Mention any two types of relays available in the market.

Ans: (i) SPST (single pole single throw)

(ii) SPDT (single pole double throw)

3. Write any one part number for npn and pnp transistor.

Ans: SL - 100 : npn transistor

SK – 100 : pnp transistor.

Three marks questions

1. Write the steps involved in PCB designing .

Ans: PCB layout preparation : PCB layout must be draw using PC. The complete circuit must be draw on a paper. Prepare computer layout as per circuit diagram using PCB design software. Draw tracks for connecting one component to the other. take printout on a white sheet and get film done on transparent sheet by film makers.

Photo-resist: Photoresist film or mask is placed in copper clad board. UV light is exposed on copper clad boaed covered by photo-resist film. UV light does not pass through photoresist on the tracks copper area which is not covered protected by photo-resist is removed during etching process.

PCB etching process: Etching process is done to remove the unnecessary copper afrer UV exposure, leaving behind only the desired copper tracks. The PCB is then dipped in ferri chloride or hydrochloric acid unitl unwanted copper is dissolved.

then the PCB is dipped in acetone to remove black colur giving the PCB a shining attractive look

PCB Drilling: The components to be attached to PCB can be done only by vias drilling ie, by drilling a hole. to make PCB good solderable the surface of the PCB is coated with tin or nickel.

PCB assembling: the electronic components are assembled on the respective holes int the

PCB. the component leads are electrically and mechanically fixed to the boaed with a solder.

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