MAHARASHTRA STATE BOARAD OF TECHNICAL EDUCATIOD (Autonomous) (ISO/IEC Certified)

Transcription

1 Subject Code: Model Answer Page 1 of 28 Important suggestions to examiners: 1) The answers should be examined by key words and not as word-to-word as given in the model answer scheme. 2) The model answer and the answer written by candidate may vary but the examiner may try to assess the understanding level of the candidate. 3) The language errors such as grammatical, spelling errors should not be given more importance. (Not applicable for subject English and communication skills) 4) While assessing figures, examiner may give credit for principle components indicated in a figure. The figures drawn by candidate and model answer may vary. The examiner may give credit for any equivalent figure drawn. 5) Credits may be given step wise for numerical problems. In some cases, the assumed constant values may vary and there may be some difference in the candidate s answers and model answer. 6) In case some questions credit may be given by judgment on part of examiner of relevant answer based on candidate understands. 7) For programming language papers, credit may be given to any other program based on equivalent concept. Q.1 Attempt any ten of the following: Marks a) State ohm s Law and write equation of finding current Ohm s Law: (2- Mark) Whenever physical condition surrounding the conductor remains constant current passing through conductor is directly proportional to potential difference of that conductor. I V, or V IR By using ohm s law finding current equation = V I R b) Write the principle on which transformer works. Working Principle: (2 Marks) The primary winding is connected to single phase AC supply. an ac current starts flowing through it. The AC primary current produces an alternating flux in the core. This Changes flux gets linked with the secondary winding through the core

2 Subject Code: Model Answer Page 2 of 28 The varying flux will induce voltage into the secondary winding according to the faraday s laws of electromagnetic induction. OR A Transformer works on the principle of Faradays law of electromagnetic induction. When their primary winding is connected to a.c supply, applied alternating voltage circulates an alternating current through it. This current flowing through the primary winding produces an alternating magenetic flux ( ).This flux links with secondary winding through the magenetic core & induces an emf in it according to the faraday s laws of electromagnetic induction. c) State two applications of stepper motor. Applications of stepper motor- 1. In Floppy disc drives. 2. In Computer printers. 3. In image scanners. 4. In compact Disc drives, etc. (Any two application expected-1 Mark each) d) What is positive and negative return system? Positive system: (1 Mark) 1. Tends to generate excessive system gain, noise, narrows bandwidth, and can cause oscillation. 2. Creates instability and tends to drive a system into its nonlinear region of operation. 3. Whereas negative feedback reduces system gain and increases bandwidth. Positive feedback increases system gain, narrows bandwidth, and becomes unstable. However, a system operating with positive feedback that hasn't gone into complete instability (oscillation), can be a very sensitive device with very high-gain amplifiers and sharp selectivity--super-regenerative radio receiver is a good example. Negative system: (1 Mark) 1. Tends to opposite excessive change (large amplitude) and wants to hold a system within a limited operating range. 2. In the case of an amplifier, it tends to reduce circuit gain and increase device operating bandwidth. 3. Tends to create system stability by ensuring linear operation.

3 Subject Code: Model Answer Page 3 of 28 e) Define analog signal and digital signal. Analog Signal:- (1 Mark) An analog signal is any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity. Digital Signal :- (1 Mark) A digital signal is a physical signal that is a representation of a sequence of discrete values (a quantified discrete-time signal), for example of an arbitrary bit stream, or of digitized (sampled and analog-to-digital converted) analog signal. f) Draw the symbol of NOR and NAND gate. (Each Symbole-1 Mark) 1. NOR Gate: 2. NAND Gate: g) What is LVDT? State two application of it. (Definition:- 1 Mark & Application: 1 Mark) Linear Variable Differential Transformer (LVDT):- It is the transducer most widely used to translate linear motion into electrical signals. Application of LVDT: (Any Two application expected) 1. Crankshaft Balancer 2. Pill Making machine 3. Testing soil Strength 4. Product inspection machine 5. Robotic Cleaner

4 Subject Code: Model Answer Page 4 of 28 h) Draw symbol and construction of NPN transistor.(construction:1 Mark & symbol:1 Mark) Construction Of NPN Transistor : Symbol of NPN Transistor: i) State the working principle of AC motor. (2 Mark) Working principle of AC motor: (Student may write any suitable answer in different ways) When AC supply given to motor winding. Rotating magnetic field is produced rotor cuts the rotating field, Which results into rotor current. Interaction of rotor current & rotating magnetic field produces torque on rotor and rotor starts rotating. j) List the two application of zener diode, also draw symbol of it. Symbol of zener diode :- ( 1 Mark) Applications of the zener diode (any two):- ( 1 Mark) 1. Voltage regulator 2. Regulated power supply

5 Subject Code: Model Answer Page 5 of In protection circuits of MOSFETs 4. In the clipping circuits 5. In the pulse amplifier k) Write names of different photoelectric type transducer. Different photoelectric type transducer are- (Any four expected: 1/2 Mark each) 1. Photo diode, 2. Photo-transistor, 3. L.D.R., 4. Solar cell, etc. l) Write working of seven segments LED display. (2 Mark) Working of seven-segment LED display:- Seven segment displays consists of Eight LEDs. Depending on the various digits and letters to be displayed, the combinations of LEDs are forward biased. e.g. suppose we want to display the digit 3, then LED a,b,g.c,d should only be forward biased.

6 Subject Code: Model Answer Page 6 of 28 Q.2) Attempt any Four of the following: Marks a) Explain the importance of colour coding in automobile wiring Importance of colour coding in automobile wiring: (4 Mark) Automobile wiring is complicated because of number of lamps and accessories for this color coding is necessary due to which wiring can easily identify for specific lamp and accessories and also it is easier during maintenance. b) Draw and explain the phasor diagrams for purely resistive and purely inductive circuit. Phasor Diagram: Purely resistive circuit: Purely inductive circuit: (Each diagram-1 Mark each) Explanation: (Each Explanation: 1 Mark each) 1. Purely resistive circuit: In a pure resistive A.C circuit current (I) is in phase with applied voltage across the resistance. 2. Purely Inductive circuit: In a pure inductive A.C circuit current (I) in lags applied voltage by 90 0 across the inductor with applied voltage across the resistance.

7 Subject Code: Model Answer Page 7 of 28 c) State the different transducers used for temperature measurement and explain working principle of any one type.. (List of Transducer-2 Mark, Figure-1 Mark & Explanation-1 Mark) Different temperature transducers- 1. Thermostat 2. Thermistor 3. Resistance Temperature Detector (RTD) 4. Thermocouple 5. Pyrometer (Any four expected: 1/2 marks each) 1. Thermocouple working principle- (2 Marks for any one temperature transducer) Thermocouple principle is based on the see beck effect which states that if the two dissimilar metals having different work functions are joined together to form a junction (hot junction)and if the junction is subjected to change in temperature then the voltage is generated at the another junction (cold junction). The E.M.F. generated is proportional to the temperature difference. OR 2. Working principle of Thermistor:- (Allotted 2 Marks ) Thermistors are one of the most commonly used devices for the measurement of temperature. The thermistors are resistors whose resistance changes with the temperature. The thermistors are made up of ceramic like semiconducting materials. They are mostly composed of oxides of manganese, nickel and cobalt having the resistivities if about 100 to 450,000 ohmcm. Since the resistivity of the thermistors is very high the resistance of the circuit in which they

8 Subject Code: Model Answer Page 8 of 28 are connected for measurement of temperature can be measured easily. As mentioned earlier the resistance of the thermistors decreases with the increase its temperature. The resistance of thermistor is given by: R = R o e k K = β(1/t 1/T o ) Where, R is the resistance of the thermistor at any temperature T in o K (degree Kelvin) R o is the resistance of the thermistors at particular reference temperature T o in o Ke is the base of the Naperian logarithms β is a constant whose value ranges from 3400 to 3900 depending on the material used for the thermistors and its composition. The thermistor acts as the temperature sensor and it is placed on the body whose temperature is to be measured. It is also connected in the electric circuit. When the temperature of the body changes, the resistance of the thermistor also changes, which is indicated by the circuit directly as the temperature since resistance is calibrated against the temperature. The thermistor can also be used for some control which is dependent on the temperature. OR 3. Working principle of RTD:- (Allotted 2 Marks ) The resistance of the material used to manufacture RTD depends upon temperature. As temperature changes resistance of RTD gets changed, the main principle of operation of an RTD is that when the temperature of an object increases or decreases, the resistance also increases or decreases proportionally (RTDs are normally PTC type ). R = Ro (1+ t ) The main difference between a RTD and a Thermistor is that the sensing element used in a RTD is a metal and a thermistor uses ceramic or polymer material. As platinum is the most commonly used metal for making RTD s, the device can also be called Platinum Resistance Thermometers (PRT s).

9 Subject Code: Model Answer Page 9 of 28 d) With neat circuit diagram, draw forward and reverse characteristic of P-N junction diode. (Circuit diagram: 2 Mark & Each characteristics- 1 Mark each) Circuit diagram of PN Junction Diode when When Forward Biased:- When Reverse Biased : V-I Characteristics of P-N Junction Diode: e) Explain operating principle of alternator. Operation of Alternator: - (Allotted 4 Mark) Working principal of Alternator is similar to D.C Generator. It also works on Faraday s Law of Electromagnetic Induction. Whenever excited rotor field is rotated by prime mover then as per Faraday s law of electromagnetic induction A.C Voltage will be induces in the Stator winding.

10 Subject Code: Model Answer Page 10 of 28 or equivalent dia. OR Student may write Alternator are operates on fundamental principles of electromagnetic induction. D.C Excitation is given to rotor, so it creates flux and rotor is rotated with the help of prime mover. Stator winding which is stationary cuts these flux so emf is induced in stator winding according to faradays law of electromagnetic induction. f) Explain working of 4:1 multiplexer with logic diagram. (Figure-1 Mark, Truth Table-1 Mark & Operation-2 Mark) Schematic Figure- Truth Table: or equivalent dia.

11 Subject Code: Model Answer Page 11 of 28 Operation: Multiplexer has multiple inputs and one output. i.e. it accepts several data inputs and allows only one of them at a time. The routing of desired data input to output is controlled by select lines. Q.3) Attempt any Four of the following: Marks a) Draw logic circuit of 2:4 decoder and explain with truth table. Logic circuit of 2:4 decoder: (Figure-1 Mark, Explanation-2 Mark & Truth table-1 Mark) In this simple example of a 2-to-4 line binary decoder, the binary inputs A and B determine which output line from D0 to D3 is "HIGH" at logic level "1" while the remaining outputs are held "LOW" at logic "0" so only one output can be active (HIGH) at any one time.

12 Subject Code: Model Answer Page 12 of 28 b) A single phase transformer has 350 primary and 1050 secondary turns. The primary is connected to a 400V, 50 Hz supply, If the net cross-sectional area of core is 50 cm 2. Find i) the maximum value of flux density in the core ii) voltage induced in the secondary winding. a) Given Data: 1-Ph Transformer, V 1 = 400V, V 2 =?, F = 50 Hz, N 1 = 350 K=? N 2 =1050 A= 50 cm 2 Step: 1: To Find Transformation Ratio= N k 2 N k (1 Marks) Step: 2: To Find Secondary Turns= k V V 2 2, 1 N N 1 3 V (1 Marks) V volt 2 V volt Step:3: Maximum value of flux density in the core E m f N m m, m wb.. (1 Marks) m B m m A , Bm wb / m or Tesla (1 Marks)

13 Subject Code: Model Answer Page 13 of 28 c) Why symbols are necessary in electrical Engineering? State necessity of wiring harness. Symbols Necessity in Electrical Engineering: (2 Marks) For proper communication engineers always use the drawing, for that we use the symbols which will communicate properly, denoting the various accessories used in the circuit. These symbols are standardized by BIS-Bureau of Indian standards or internal electrotechnical commission. An important consideration in selecting symbols is that they should be self explanatory & ease to draw. Necessity of Wiring Harness: (2 Marks) Automobile wiring is complicated and critical to setup, with the help of harness time required for completion of wiring is less it easy to replace and maintain other accessories like audio, video or mobile can be setup inside the vehicle, with proper instructions it can be easily installed and replace safely. d) Draw symbols of OR, AND logic gates with their truth table. OR Logic gate: AND gate : (Each symbol -1 & each Truth table-1 Mark)

14 Subject Code: Model Answer Page 14 of 28 e) With neat diagram explain working of ultrasonic flow meter. (Diagram- 2 Marks & Working Principle-2 Marks) Ultrasonic flow meter Schematic diagram:- There are two types based on 1) Doppler effect 2) Transit time. or equivalent dia. Working- Ultrasonic flow meter based on Doppler effect is explained here. A and B are piezo-electric devices transmitting the short duration ultrasonic signals through the fluid that is flowing through the pipe at a velocity v. Similar type of crystals are used as receivers to respond to pressure fluctuations. Due to the fluid velocity v aiding the transmission, the velocity of ultrasonic signal from the transmitter-a to receiver-a is increased to a value c + v cos θ, where c is the velocity of sound through the fluid in the pipe and θ is the angle between the path of sound and the pipe valve. The repetition frequency of the received pulse f A will be c v cos f A l Where l= the distance between the transmitter and receiver. On the other hand, the velocity of the ultrasonic signal transmitted by transmitter B and received by received B will be reduced by the fluid velocity causing a retardation of v cos θ and its pulse repetition frequency f B will be c v cos f B l The difference between frequencies is given by 2v cos f f A fb l By measuring the difference in the repetition frequency f and knowing the values of θ and l, the velocity of the fluid can be computed alternatively, the flow velocity can be computed by measuring the transit time difference between the two pulse trains in either direction.

15 Subject Code: Model Answer Page 15 of 28 f) Draw neat diagram of bridge rectifier. Explain its working with input-output waveforms. Working of full bridge Rectifier: (Figure-2 Mark & Explanation-1 Mark, Wave form-1 Mark) OR Equivalent Fig. Working:- In the positive half cycle, D1and D4 are forward biased (D2and D3 are reverse biased). In the negative half cycle, D2and D3 are forward biased (D1and D4 are reverse biased). The output voltage is obtained in both half-cycles of input signal. The advantage is that PIV rating of diodes are Vm and center-tapped transformer is not required. The main disadvantage is that it requires four diodes. Waveforms:-

16 Subject Code: Model Answer Page 16 of 28 Q.4. Attempt any four of the following: Marks a) Compare core type and shell type transformer on the basis of i) Capacity ii) construction iii) Cost iv) Application (1 Mark each point) S.No Point Core Type Transformer Shell Type Transformer 1 Capacity Less More 2. Construction The Winding surround the core, Average length of the core is more, Magnetic Flux has only one continuous path and less in weight The core surround the windings, Average length of the core is less, Magnetic Flux is distributed into 2 paths and more in weight 3 Cost Less More 4. Application Suitable for high voltage & less Suitable for less voltage & high output output b) Draw speed-torque characteristics of i) D.C. series motor ii) D.C. shunt motor i) Speed-Torque Characteristics of D.C. Series motor: (Marks -2) ii) Speed-Torque Characteristics of D.C. Shunt motor: (Marks -2) ZNP Eb 60A N E V I R b a a (since all other constant) From these N E V I R b a a decreses as shown in the graph. it is clear that as load increses I a R a drop increses hence speed

17 Subject Code: Model Answer Page 17 of 28 c) Write four applications of shift registers and counters. Applications of shift registers: 1. Parallel to serial conversion 2. Pattern recognition 3. Serial data communication 4. To produce time delay 5. To simplify combinational logic Applications of counters: (2 Mark) (2 Mark) 1. To divide clock frequencies 2. In basic digital clock 3. In F/V and V/F converter 4. Visitor counter d) Explain measurement of force by load cell with diagram Strain Gauge load Cell:- Construction: (Construction-2 Mark & Explanation: 2 Mark) Working- or equivalent dia. This is consists of a fine wire element is loop back and forth on mounting plate (base). A tensile stress tends to elongate the wire and thereby increase its length and decreases its crosssectional area. The combined effect is an increase in resistance. The strain of wire grid is measured with the Wheatstone bridge connecting the gauge in one of the four arms. When the force is applied on load cell, the resistance of load cell changes in accordance with the applied force.

18 Subject Code: Model Answer Page 18 of 28 e) Compare insulated and ground return system (any four parameters) Sr.No Insulated Return Ground Return (1 Mark each point) 1 Actually wire is used a return path for current Actually ground is used as a return path for current No wire is required 2 Number of wires require Two Number of wire required one 3 There is no disadvantage such as steel which is underground get rusting when insulated wire is used as a return path If ground is used as a return path than there is disadvantages such as steel which is underground get rusting 4 Cost is more Cost is less f) Draw symbols of LED, SCR, TRIAC, PNP transistor 1) Symbol of LED :- (1 Mark) 2) Symbol of SCR:- (1 Mark) 3) Symbol of Triac:- (1 Mark) 4) Symbol of PNP:- (1 Mark)

19 Subject Code: Model Answer Page 19 of 28 Q.5) Attempt any Four of the following: Marks a) Define the following terms: i) Permeability ii) Reluctance iii) Magnetic field intensity iv) Magnetic flux i) Permeability: (1 Mark) Permeability is a measure of the ability of a material to permit the setting up of magnetic flux in it. It is represented by (M u ) OR Permeability ( ) Flux density ( B) Magnetisin g force ( H ) ii) Reluctance (s) :- (1 Marks) Reluctance is the property of the substance which oppose the creation of flux in it. iii) Magnetic field intensity: (1 Mark) If the magnetic circuit is homogeneous and of uniform cross sectional area, the magneto motive force (M.M.F) per unit length is called magnetic field intensity. Magnetic field int ensity ( H ) M. M. F Length iv) Magnetic flux ( ) :- (1 Mark) The total number of lines of force comprising the magnetic field is called magnetic flux m.wb b) Explain battery ignition and magneto ignition. (Each Explanation-2 Mark) 1. Battery Ignition System (2 Mark) In this case 6 V or 12 V batteries will supply necessary current in the primary winding. The Battery ignition system is divided into 2-circuits:

20 Subject Code: Model Answer Page 20 of 28 (i) Primary Circuit: It consists of 6 or 12 V battery, ammeter, ignition switch, primary winding it has turns of 20 SWG (Sharps Wire Gauge) gauge wire, contact breaker, capacitor. 53 Ignition Systems (ii) Secondary Circuit: It consists of secondary winding. Secondary winding consists of about turns of 40 (S WG) gauge wire. Bottom end of which is connected to bottom end of primary and top end of secondary winding is connected to centre of distributor rotor. Distributor rotors rotate and make contacts with contact points and are connected to spark plugs which are fitted in cylinder heads (engine earth). 2. Magneto System: (2 Mark) In this case magneto will produce and supply the required current to the primary winding. In this case as shown, we can have rotating magneto with fixed coil or rotating coil with fixed magneto for producing and supplying current to primary, remaining arrangement is same as that of a battery ignition system. In this case magneto will produce and supply current to the primary winding. So in magneto ignition system magneto replaces the battery. c) What are the main parts of D.C motors? State the function of each part. (Figure-1, & Function of any three part -1 Mark each part) OR Equivalent Fig

21 Subject Code: Model Answer Page 21 of 28 Function : (Any three part expected) 1) Yoke: The main frame of machine is called the yoke. The yoke serves the following two purposes. i) It supports the other components such as poles and provides mechanical protection for whole machine. ii) It forms a part of the magnetic circuit & provides the path of low reluctance for the magnetic flux. 2) Pole Cores & Pole shoe: The pole core and pole shoe from an important part of the field system. The pole shoe serves two purposes i) They spread out flux in the air gap & their large cross section reduces the reluctance of the magnetic path ii) They support the exciting coils or field coils. 3) Armature core: The armature cores, which is cylindrical or drum and built up of circular sheet discs or laminations is keyed to the shaft. It serves two purposes i) Houses the armature conductors or coils and causes them to rotate, hence cut the magnetic flux ii) Provides a low reluctance path to the flux through armature 4) Armature winding: The armature winding consists of a large number of coil suitably connected together 5) Commutator: The function of the commutator is to reverse the current in each conductor of the armature as it passes from one pole to another and thus to help the motor to develop a continuous and unidirectional torque 7) Brush: Brushes are used to conduct the current to the commutator from the external circuit. 8) Cooling Fan: In some machine, A fan is fitted to the shaft on the side opposite to that of the commutator for cooling purposes. 9) End covers: These are attached to the ends of the main frame and contain bearings for the armature. The end cover on the commutator side also supports the brush assemblies.

22 Subject Code: Model Answer Page 22 of 28 d) State the principle of piezo-electric transducer with diagram. (Figure: 2 Mark & Explanation: 2 Mark) A piezoelectric transducer / sensor is a device that uses the piezoelectric effect, to measure changes in pressure, acceleration, strain or force by converting them to an electrical charge. There are certain materials that generate electric potential or voltage when mechanical strain is applied to them or conversely when the voltage is applied to them, they tend to change the dimensions along certain plane. This effect is called as the piezoelectric effect. Some of the materials that exhibit piezoelectric effect are quartz, Rochelle salt, polarized barium titanate, ammonium dihydrogen, ordinary sugar etc. OR The piezoelectric transducers work on the principle of piezoelectric effect. When mechanical stress or forces are applied to some materials along certain planes, they produce electric voltage. This electric voltage can be measured easily by the voltage measuring instruments, which can be used to measure the stress or force. The physical quantities like stress and force cannot be measured directly. In such cases the material exhibiting piezoelectric transducers can be used. The stress or the force that has to be measured is applied along certain planes to these materials. The voltage output obtained from these materials due to piezoelectric effect is proportional to the applied stress or force. The output voltage can be calibrated against the applied stress or the force so that the measured value of the output voltage directly gives the value of the applied stress or force. In fact the scale can be marked directly in terms of stress or force to give the values directly.

23 Subject Code: Model Answer Page 23 of 28 e) State the working principle of contact less electrical tachometer Contactless electrical tachometer- (2-Mark) Construction- or equivalent principle dia. Working- (2- Mark) This consists of mounting an opaque disc on the rotating shaft. The disc has a number of equidistant holes on its periphery. At one side of the disc a light source is fixed and at the other side of the disc, light sensor is placed. When the opaque portion of the disc is between the light source and the light sensor, no output is produced. When a hole appears between the two, the light falling upon the sensor produces an output pulse. The frequency at which these pulses are produced depends upon the number of holes on the disc and its speed of rotation. The pulse rate can be measured by an electronic counter which can be directly calibrated in terms of speed in rpm. f) Draw symbol and working of phototransistor. Also state two application of it. (Symbol:1 Mark, Working : 2 Mark and Application: 2 Mark) Phototransistor - Schematic diagram

24 Subject Code: Model Answer Page 24 of 28 Working The phototransistor has a light sensitive collector to base junction. A lens is used in a transistor package to expose base to an incident light. When the base is exposed to the light, the base current is produced which is proportional to the light intensity. When no light is incident, a small leakage current flows from collector to emitter due to small thermal generation. Application of Phototransistor: 1. Burglar Alarm 2. Smoke detectors 3. Remote control devices 4. In CD players Q.6) Attempt any Four of the following: Marks a) Draw connection diagram of ammeter, voltmeter for a DC load. Write four applications of multimeter. Connection diagram of ammeter, voltmeter for a DC load: (2 Mark) Following Four Applications of multimeter: (Each point 1/2 Mark) 1. To measure AC & DC voltage 2. To Measure AC & DC Current 3. To measure the value of resistance 4. To check the circuit continuity test

25 Subject Code: Model Answer Page 25 of 28 b) What is oscillator? Write its four applications. (2 Mark) An electronic oscillator is an electronic circuit that produces a repetitive, oscillating electronic signal, often a sine wave or a square wave. Oscillators convert direct current (DC) from a power supply to an alternating current signal. Applications: (Each application: 1/2 Mark each) 1. Radio and television transmitters 2. Computer clock circuits 3. Electronic beepers 4. In inverter and UPS c) Explain concept of electrical method for moisture measurement. (Marks -4) Following are the different methods for moisture measurement: i) Resistance Moisture measurement ii) Dielectric Moisture measurement iii) In-line Moisture measurement OR Explanation of electrical method for moisture measurement Moisture can produce a marked increase in the electrical conductivity of material, and because of waters high dielectric constant, capacitance measurement can be also valuable. Electrical resistance measurement of moisture in timber and plaster are generally made using a

26 Subject Code: Model Answer Page 26 of 28 pair of sharp pointed probes, which are pushed in to material. The meter on the instrument being calibrated directly in percentage moisture. d) Define the following terms: i) Power factor ii) Reactive power iii) Frequency iv) Resistance i) Power factor: (1-Marks) i) It is ratio of true power (active power) P to the apparent power S Active Power ( P) P. F OR Apparant Power ( s) ii) It is defined as cosine angle between voltage and current. OR iii) It is the ratio of resistance R to the impedance Z. Re sis tance ( R) Cos OR Im pedance ( Z ) i) Power factor is defined as how much current is utilized out of total current ii) Reactive Power (Q):- (1 Mark) The reactive power is defined as the product of voltage and current (V, I) and sine of angle between voltage (V) and current (I ) i.e. Q= V.I. sin Units: - VAR OR KVAR iii) Frequency: frequency. (1 Mark) The number of cycles completed by an alternating quantity in one second is called as It Unit: Hertz (Hz) iv) Resistance: (1 Mark) It is defined as the opposition offered by a conductor to the flow of current. It is represented by R OR The formula for resistance is given by l a OR R=V/I Unit ohm R=

27 Subject Code: Model Answer Page 27 of 28 e) Draw neat circuit diagram of common emitter amplifier. Draw neat V-I characteristics of SCR and State its two application Common emitter amplifier- (Diagram: 2 Mark, Characteristics:1 Mark & Application:1 Mark) V-I characteristics of S.C.R Applications of S.C.R: 1. Chopper 2. Inverter 3. Drives, etc.

28 Subject Code: Model Answer Page 28 of 28 f) Write four difference between mechanical and electrical/electronic instruments (Any four point expected- 1 Mark each point) S.No. Mechanical Instruments Electrical/Electronic Instrument 1 These instruments are used for static & stable condition. Or sensitivity of the electrical instrument is less 2 They are unable to respond rapidly to measurement of dynamic & transient condition. 3 Instruments are consists of moving parts that are rigid, heavy & bulky. These instruments are used for rapid changes. Or sensitivity of the electrical instrument is more They are able to record dynamic & transient condition. Instruments are consists of moving parts that are light in weight. 4 Weight is more. Weight is less. 5 It produce noise & causes air pollution. It doesn t produce noise during measurement. 6 Slowly indicates output. Rapidly indicates output. 7 Life of the mechanical instrument is more Life of the electrical instrument is less