[For Railway & Other Engineering (Diploma) Competitive Examinations]

By Prof. Tejpal Suman

Upkar Prakashan, Agra-2 © Publishers

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ISBN : 978-93-5013-582-2 Price : ` 165.00 (Rs. One Hundred Sixty Five Only)

Code No. 1864

Printed at : UPKAR PRAKASHAN (Printing Unit) Bye-pass, AGRA Contents

1. Electronic Equipments ...... 3–18

2. D.C. Generators ...... 19–31

3. D.C. Motors ...... 32–44

4. Bipolar Junction (BJTs) ...... 45–53

5. ...... 54–63

6. Field-Effect Transistor ...... 64–74

7. Number Systems and Codes ...... 75–82

8. Electronic Analog as well as Digital ...... 83–91

9. Optoelectronic Devices ...... 92–100

10. Transducers ...... 101–109

11. Cathode Ray Oscilloscope ...... 110–119

12. A.C. Three Phase Motors ...... 120–131

13. Single Phase Motors ...... 132–147

14. Meters ...... 148–159

15. Alternators ...... 160–169

16. Transformers ...... 170–178

17. Polyphase ...... 179–188

18. Fundamentals of Electricity ...... 189–200 A Handbook on ELECTRONICS 1. Electronic Equipments

UU In pro-electron code system for UU are called bipolar devices because conduction components, for the component BY127 ‘B’ and ‘Y’ is due to both hole and electron currents. respectively stand for and rectifier . UU The maximum reverse voltage that a diode can UU The cut-in (threshold or keen) voltage of By1127 withstand, is referred to as peak-inverse-voltage. rectifier diode is 0.7 V. UU A forward biased diode starts conducting when the UU The PIV rating of IN4007 rectifier diode is 1000 V. applied voltage reaches certain voltage known as UU The two most important electrical specification for a barrier voltage. rectifier (power) diode are PIV and IF. UU In JEDEC system of coding semiconductor com­ UU The cathode lead of OA79 diode is identified by a ponents 1 N represents on PN-junction. coloured dot at one end. UU The JEDEC equivalent for BY 127 diode is IN4007. UU Each letter in the semi-conductor coding gives UU The maximum voltage (peak to peak) that can be specific information. In the transistor AC 128 letter generated by a function generator is 20 V. . UU The function selector is used to select the desired wave UU In the BZ 148 , the second letter form. Z-indicates the device is a zenerdiode UU The selected wave form in a function generator is UU The second letter ‘F’ in transistor condification indicates available at output jack. H.F. transistor. UU The effect of amplitude control on TTL output is UU The diagram useful to identify the leads of the amplitude remains constant. and other semiconductor devices in known as base UU The main difference between function generator and diagram. the AF generator is that the function generator produces UUWhich element is used as a semiconductor sine wave, square wave, triangular wave but AF material? (Silicon) generator produces triangular wave. UU Valence electrons are those which occupy the outermost UU AF generator has a frequency range upto 100 kHz. shell. UU The maximum signal amplitude output from a AF UU The number of valence electrons of the element silicon generator will be 20 V. (whose atomic number is 14) is 4. UU In AF generator the lowest frequency starts from 20 UU The number of valence electrons of a semiconductor Hz. element is four. UU The function of a is to maintain a constant UU The temperature coefficient of resistance of a output voltage. semiconductor is negative. UU The connection of a zener diode in a circuit is UU Silicon is used as a semiconductor material. always reverse biased. UU The temperature coefficient of resistance of a UU At the breakdown region of a reverse bias, the semiconductor is Negative. zener diode current begins to increase rapidly. UU The main characteristic of any diode is that it lets current UU Once the zener diode enters into the breakdown region flow in only one direction. the factor that does not change much is the voltage. UU The width of the depletion region of a junction is UU In a zener voltage regulator circuit the resistance is to reduced under forward bias because the majority be connected in series, with the supply when the load careers on both sides of the junction are driven is connected across the zener diode. towards it. UU The value of current in a zener diode is limited by the UU The width of the depletion layer of a junction is external circuit resistance. increased under reverse bias. UU How the cathode of a zener diode is represented in its UU When forward bias is applied in a junction diode, it symbol? decreases the potential barrier. UU How the cathode of a zener diode is represented in its UU The silicon junction diode starts to conduct when symbol? (The letter ‘Z’) the voltage across the junction reaches is 0.7 V. UU The output voltage of a zener diode regulated power UU The voltage across the depletion layer for a germanium supply remians practically constant because of the diode is 0.3 V. voltage drop in series resistance changes with change UU The barrier voltage across a PN-junction of a silicon in load current. diode at 25°C is 0.7 V. UU The unregulated input voltage is different from the 4 A Handbook on Electronics output voltage of P regulator circuit in the sense it is UU In the case of LED a typical forward current ranges higher. from 1 mA to more than 50 mA. UU Which is the element added to intrinsic semiconductor UU The special type of LEDs which can emit more than material as impurity to produce P-type semiconductor? two colours are mounted 3 pin common cathode (Indium) package. UU The intrinsic semiconductor at room temperature UU A photo diode can turn its current ON and OFF in inducts leakage current like in insulators. nanoseconds. UU The width of the depletion layer of a junction is UU The maximum reverse voltage that can be applied for increased under reverse bias. the chosen LED in 8.0 volts. UU Antimony elements used as impurity to produce N-type UU Carbon tetra chloride is not used for etching. semiconductor. UU The typical ratio of ferric chloride and water for making UU Defecting plate in a CRT is used to control the path of etching solution is 1 : 10. electrons. UU The time taken for etching PCBs is in the range of 5 to UU The emission of electrons in CRT is due to indirect 10 minutes. heating of cathode. UU The PCB side on which components are mounted UU Control grid controls the number of electrons. is referred to as component side. UU Deflection plates in a CRT deflects electron beam UU Horizontal mounting of the component on PCB, is vertically and horizontally. preferred in specific cases where it takes more space UU A CRT screen is coated with phosphor. but more stable. UU Sychronisation of time base signal and input signal is UU Correct way of soldering is heating the joint and performed by Trigger. applying solder. UU The brightness on the screen of a CRO is the UU The solder wire used in electronic soldering work melts characteristic of the coating material of the screen. at 200°C. UU The attenuator in a CRO is used to vary input voltage UU To solder resistors on a PCB, the soldering iron to suit the amplifier in CRO. wattage should be 25 W. UU Control grid electrode of the CRT mainly controls the UU The critical factors during soldering are controlling the brightness of the image on the screen? temperature and time of heating. UU The difference between an oscilloscope and a multimeter UU Ideally the soldering tip face should be equal to is the oscilloscope can show the wave-forms but the the area of the joint to be soldered. multimeter can measure only the magnitude. UU Potentiometers are used where you need a variable UU In order to obtain the stationary pattern of an oscilloscope resistance value. in a.c. signal measuring, what should be adjusted? UU Wire wound variable resistors are generally of slide [Time-base, (Time/DIV)1] type. UU The screen graticule is calibrated for 5 V/Cm. The height UU Variable resistor will have only one terminal. of the sine wave from is 6 cm. The amplitude of the UU Value of variable resistor is indicated by value printed wave form will be 30 VP-P. on the body. UU When the potential difference between the horizontal UU Variable resistors are available as both linear and plates becomes zero, the dot on the oscilloscope logarithmic type. screen is at the centre. UU Unlike ordinary potentiometers, in some potentio­ UU The frequency of the internal horizontal sweep is 25 Hz meters the shaft can be rotated by more than one with the vertical input at 50 Hz. How many cycles will turn. Such potentiometers are called presets. appear on the screen of the CRO? (Two) UU An amplifier is used to obtain an increased voltage, UU The connection of a zener diode in a circuit is current or power of an input signal. always reverse-biased. UU In the case of a common-emitter amplifier the output UU Once the Zener diode enters into the breakdown region voltage wave-form is always lagging by 180° with the factor that does not change much in the voltage. respect to input voltage wave-form. UU At the breakdown region of a reverse biase, the UU An ideal voltage amplifier should have high input Zener diode current being the increase rapidly. impedance and low output impedance. UU In a Zener diode circuit the resistance is to be connected UU An amplifier circuit with gain of 200 has an output in series with the supply when the load is connected voltage equal to 2 V. Then the input voltage will be 10 across the diode. mV. UU The value of current in a Zener diode is limited by the UU In an amplifier the maximum power transfer to the external circuit resistance. load resistance should be equal to the value of the U output resistance. U In the case of LEDs unlike general purpose diode, I the forward voltage of LED ranges from 1.5 to 3 UU The current gain of CE amplifier is the ratio of C . volts. Ib A Handbook on Electronics 5 that correspond to the ON/OFF switch terminals are Vinput UU The input impedance of an amplifier is . collector and emitter. Iinput UU Transistor is said to be in the cut off state when its UU The base materials used for making PCBs are fiber, VBE = 0 and VCE = 0. glassy epoxy. UU To construct electronics circuit, the board used in radio UU The unit used for specifying thickness of the copper foil receiver is printed circuit board PCB. on a PCBs is ounce per square foot. UU For connecting the number of electronic components UU The circular rings of copper on the PCB for making to one point lug board is used. solder connections of components leads are called UU While preparing PCB, the circuit pattern on the copper pads. laminated board is made by the process called as UU The chemical used for removing copper from copper etching. clad boards is called etchant. UU In small signal operation, the peak to peak swing of lc UU In amplifiers transistors are used for enlarging small should be less than 10% of lc at Q point. electric signals. UU The amplifiers which retain the shape of the input signal UU A transistor can be thought of as two PN junction diodes at the output are called linear amplifiers: connected as PNNP. UU The functions of the emitter by pass capacitor in a CE UU NPN transistors are preferred to PNP transistors for amplifier is to provide a low resistance path for the ac higher switching speed. signals. UU Small signal amplifiers are also known as low power UU The effect of the emitter by pass capacitor in a CE amplifiers. amplifier is increased gain and input impedance. UU The three terminals of a bipolar transistor are emitter, UU In a CE amplifier the low and medium frequency gain collector and base, depends on coupling capacitors. UU A transistor has two PN-junctions. UU For an audio amplifier (20 Hz to 20 kHz) the minimum UU The number of depletion layers in a transistor is two: value of the input coupling capacitor should be at least UU In an NPN transistor, P region is called base. 4.7 μF. UU A transistor is a current operated device. UU The cut-off frequency is also known as half power UU At the base emitter junction of a transistor, one finds point because at this point the load power is half low resistance. of its maximum value. UU While testing the PN junctions of a transistor using an UU In a CE amplifier, the voltage gain at the cut-off ohmmeter, middle range such as R 100 ohms is frequency is 0.707 times its maximum (mid-frequency) preferred. value. UU The most suitable soldering iron for soldering small UU The gain of a CE amplifier is highest at mid- transistor is 15-25 W. frequencies. UU The lead length of transistor from the case to the bend UU The highest frequency that can be amplified by an should be at least 5 mm. amplifier is limited by internal by capacitances of UU Transistors are very sensitive to all the three parameters the transistor. mentioned above. UU In a CE amplifier, collector voltage is found to be zero. UU Which is a disadvantage in the case of transistors The reason could be + Vcc is zero. compared to vacuum tubes? UU In a CE amplifier, with RE in the circuit, LE is zero. (Sensitivity to temperature) The reason could be BE junction is reverse biased. UU The purpose of mounting transistors on metal plate is UU In a CE amplifier, output signal is less than the input to radiate the excessive heat of transistor case. signal. The reason could be bypass capacitor CE is U U In a transistor, the base current, is less than 5% of emitter leaky. current. UU In a CE amplifier, the bypass capacitor CE gets heated U U For transistor action the base region must be very up excessively. The reason could be CE is connected in narrow. reverse polarity. U U When a transistor is operated as a switch it operates UU The component which fails most frequently in an between the cut off and saturation points. amplifier is electrolytic capacitor. U U A transistor is said to be in a saturated state when UU A power amplifier is essentially a current amplifier. VCL UU Class A amplifier conducts during the entire 360° of the IC = RL sine wave input. UU The transistor is made to work as a switch because UU Lack of symmetry in the amplitude of the signal the conduction is heavy on reaching saturation and applied to the two transistors of a push pull does not depend on the base current increase. amplifier results in distorted output. UU When a transistor is used as a switch, the terminals UU The degree by which the output signal wave shape 6 A Handbook on Electronics differs from the input signal wave shape is known as UU Triac is basicaly a Bi-directional device. distortion. UU Operations of are restricted to the following UU Class A amplifier is used as the first amplifier stage in quadrants as per the characteristic curves 1st and 3rd. many applifications due to its low distortion. UU Triac is least sensitive in the 3rd quadrant mode when UU In class B amplifiers the output current flows only for MT1 is positive in the 3rd quadrant +ve gate singal. one half of the input cycle. UU When triac is ‘ON’ the current flowing between MT1 UU Efficiency of a class B push-pull amplifier is typically and MT2 is known as holding current. around 50 - 80%. UU The triac will remain ‘ON’ condition as long as the UU The output stage of a complementary symmetry class current flowing through it is larger than holding B amplifier uses one pnp and one npn transistors. current. UU Which of the following is a disadvantage of class-B UU A triac when tested by a ohmmeter will show a higher push-pull amplifiers cross over distortion. resistance in the order of 1 Megohm between UU The purpose of complementary symmetry arrange­ terminals MT2 negative and 4 positive MT1 positive ment is push-pull amplifiers is to eliminate output G negative. transformer. UU A triac when tested by a ohmmeter will show a lower U U In class-B amplifier, the Q point is set slightly above resistance in the order of 300 ohms between terminals cut-off. The purpose is to avoid cross-over distortion. MT1 positive G negative. U U Solar cells are basically photo-diode. UU One way to differentiate diac and triac is that Triac has UU Solar cells are also named as photovoltaic cell. three terminals and diac has two terminals. UU Each solar cell has a open circuit voltage equivalent to UU In a triac, terminals are marked as Main terminal 1, 0.55 V. Main terminal 2 gates. UU Output of the solar cell per cm square depends upon UU For full wave rectification we need minimum one one of the factors given below. Identify it doping level triac. of p-n material and thickness of p-material. UU To suppress radio frequency interference we have to UU To satisfy the given voltage supply requirement, several incorporate a low-pass filter circuit. solar cells should be connected in series. UU At higher frequencies a capacitor acts as a short UU For the given current requirement of load the solar cells circuit. should be connected in parallel. UU At higher frequencies an inductor acts like a open UU Running cost of solar cell energy converters will be circuit. economical when compared to diesel generating sets. UU Incandescent lamps and heaters can be operated through UU Air pollution is the least in this type of energy converter AC and DC supplies. solar cell energy converters. UU Advantage of semi-conductor lamp dimmer and motor UU Solar cells are not popular in India due to the fact that speed control devices is low power wastage. UU Soft start lamp dimmers are especially useful for intital cost is high in solar .energy converters. UU Diac can be used to trigger the following devices : Triac/ projection lamps. SCR. UU By controlling the field current of a DC shunt motor UU Diac can be triggered in any direction using positive or only above normally speed can be achieved. negative pulses. UU By controlling the armature voltage of a DC shunt motor UU Diac is a semi-conductor devices having three layers, only below normal speed can be achieved. two terminal devices. UU Speed control circuit having 2 SCRs and 2 diodes UU Diac is doped with equal impurities in p and n type in bridge formation enables the motor armature to material. have high average value of voltage with full wave rectification. UU Diac can be switched ‘OFF’ when the current UU To control the speed of a DC motor, we can use a through the diac falls below turn-on current. SCR and diode bridge circuit connected to an AC 240 U U Diac characteristic exhibits negative resistance co- V 50 Hz supply. When the applied AC voltage is normal, efficient. the input DC to motor depends firing angle of the U U By using ohmmeter to test the diac we can find the SCR. condition of diac with respect to short between its UU Speed control methods using SCR could not be applied terminals. to synchronous motor. UU Break over voltage of normal diac falls between 20 to UU Universal motors whose speed to be controlled through 40 V. SCR based circuit will have pulsating torque at low UU Normal voltage drop across the diac will be in the order speed. of 0.5 to 1 V. UU In SCR based speed control circuit, false triggering UU A triac can conduct in the direction of MT1 to MT2 and is induced due to induction effect. To avoid false MT2 to MT1. triggering, we should incorporate snubber circuit A Handbook on Electronics 7 which is actually a circuit having resistor and UU Resonance of a circuit is the condition where capacitor in series. capacitive reactance equals inductive reactance. UU To reduce the radio frequency interference in the UUThe frequency of a turned circuit at resonance is circuit using Triac or SCR, we should have in the 1 fr = . circuit inductor and capacitor in this input side. 2πLC U U Universal motors could be operated by any one of the UU A wave trap is a resonance circuit. supply AC or DC. UU In a series RLC circuit, above the resonant frequency UU In a amplifier, feeding back the 180° out phase signal the net reactance is inductive to input, then the feedback is known as negative UU In a series RLC circuit, below the resonant feedback. frequency, the net reactance is capacitive. UU When negative feedback is used in amplifiers, it U results in reduced distortion. U The net reactance of a series RLC circuit at resonant frequency is zero. UU For stabilising the gain in an amplifier negative feedback X UU The Q factor or a coil is L is used. R UU Automatic volume control incorporates -ve feedback. UU A series resonance LC circuit used to reject an undesired UU In a CE amplifier, if the RE is not bypassed with a frequency is known as wave trap. capacitor, the feedback is known as current series L UU Q of the series RLC circuit is given by Q = feedback. . RC UU In a common collector amplifier input to base and output U from emitter. U In parallel resonance, the IL and Ic are out of phase with UU A CE amplifier is used to match high input impedance each other. source to a low output impedance load. UU The parallel resonance circuit is common in high UU The other name for the common collector amplifier is frequency circuits above 500 kHz. emitter follower. UU Above the resonance frequency the parallel UU The main application of a cc amplifier is a impedance resonance circuit becomes capacitive. matching circuit. UU The reactance of a series R-L-C circuit above resonant UU A cc amplifier is also known as emitter follower because frequency is inductive. the voltage at emitter follows the voltage at base. UU The reactance of parallel R-L-C circuit above resonant UU The current gain of a common base amplifier is less frequency is capacitive. than 1. UU The impedance of the parallel R-L-C circuit at resonance UU The current gain of a CB amplifier is expressed by the is maximum. symbol alpha (a). UU In the case of parallel resonant circuit the response of IC UU The current gain of a CB amplifier is equal to . the circuit at resonance frequency is in terms of IE UU The input resistance of a CB amplifier is very low. impedance. UU A microphone is a transducer which converts sound UU In a parallel LC circuit, a small current is supplied to energy into electrical energy. compensate the loss in the circulating energy. This UU A multistage amplifier consists of more than one current is called make-up current. stage. UU The oscillators which produce non-sinusoidal wave UU In a three stage amplifier if the first stage gives a forms are known as relaxation oscillators. gain of 50, the second stage 10 and the third 5, the UU An electronic circuit which produces voltages that vary overall gain of the amplifier will be 2500. in a regular fashion is known as oscillator. UU Direct coupled amplifiers are used for all the purposes UU The essential requirement to build an RC oscillator is mentioned above. an amplifier and a feedback circuit. UU The technique of connecting the output of an amplifier UU An RC oscillator uses +ve feedback. stage to the input of the next stage is called coupling. UU The amplifier works as an oscillator when loop gain U U A tuned circuit consists of two conductors and a becomes infinity. capacitor. UU In phase shift oscillator, the feedback voltage in phase UU This total impedance ‘Z’ of a series resonance circuit is shift from output to input by 180°. 22 given by ZR=−()XXLC− UU In RC oscillator using 3-RC networks for feedback each UU Resonance circuits are used in amplifiers and RC section gives a phase shift of 60°. oscillators. UU In the practical RC phase shift oscillator, a small UU The amplifier which amplifies single frequency or a capacitor is connected in shunt with the input. Its small band of frequencies is called tuned amplifier. purpose is to bypass unwanted high frequency UU The narrow band or tuned amplifier is used in radio oscillation to ground. receivers and television receivers. UU In a RC phase shift oscillator, the transistor is 8 A Handbook on Electronics replaced with another, where a value is less than UU The current carrying capacity of 1.5 sq. mm aluminium the minimum required value. what will happen? cable is 8 amps when enclosed in conduit and used in (Oscillation will not sustain) single phase AC circuits. UU The frequency of an oscillator which uses a resonant UU According to B.I.S. recommendations, the current 1 carrying capacity of cables is specified for 40°C for circuit is given by the equation . 2π LC ambient air temperature. UU Stranding of cables is done to increase flexibility and UU The feedback given to an oscillator to sustain oscillations mechanical strength and current capacity. is positive feedback. UU At increased ambient temperature, the current carrying UU The amplitude of undamped oscillations is constant. UU Series-fed Hartley oscillators are not preferred due capacity of the conductor decreases. U to their poor stability of oscillations. U When the same conductors are replaced in 3 phase UU The main difference in Colpitt’s oscillator circuit, circuits from a single phase circuit, the current carrying compared with Hartley’s oscillator is the split capacity is reduced. capacitor. UU For the same area of cross-section, aluminium UU The frequency of oscillation in a Colpitt’s oscillator is conductors carry less current when compared to copper 1 conductors. given by the expression . 2π LC UU For the same current, when compared to circuits UU While triggering SCR by UJT based relaxation protected by HRC fuses, the circuits protected by HRF oscillators the firing angle could be varued from zero fuses, the circuits protected by rewirable fuses should to 180°. have larger size cables. UU One of the advantages of using UJT based relaxation UU Aluminium conductors/cables are brittle hence they oscillator as triggering circuit for SCR is output should not be bent or twisted while laying. impedance of UJT is low. UU In cable terminations, aluminium cable ends should be UU While measuring the size of the bare conductor with a coated with anti-corrosive grease to avoid corrosion. standard wire gauge the conductor should only be UU Aluminium sleeves are used only for aluminium cleaned with clean cotton cloth. conductors. UU While inserting a bare conductor in the notch of the UU A satisfactory connector for aluminium will exert about standard wire gauge for measuring the size of the the same overall pressure as one satisfactory for copper conductor it should be neither loose nor tight. but will provide considerably more contact area such UU The possible minimum reading which can be taken by that the unit stress is less. 0 – 25 mm outside micrometer is 0.01 mm. UU When aluminium conductors are to be connected to UU In a metric micrometer one full rotation of the thimble copper conductors, we have to use bimetallic connectors gives the longitudinal movement of the spindle equal to avoid galvanic corrosion. to 0.05 mm. UU Sharp pointed screws in connectors should be avoided/ U U The anvil and spindle faces of an outside 0.25 mm flattened /filed in aluminium cable end terminations and micrometer are kept in normal contact. Later the thimble they damage the conductors. is turned to get a 0.25 mm gap between the faces. To UU Where bolted terminal connections are provided get that gap the thimble is turned half of a complete aluminium cables, reasonably large flat washers should rotation. be provided. UU The most commonly used metals for electrical UU If a connector is made up of a metal different from that conductors are: of the conductors, the difference in the rate of expansion (a) copper and contraction of the metals due to change in (b) aluminium UU While removing the insulation of a cable, the knife is temperature will cause contact pressure to oxide kept at an angle of 20° to avoid nicks in the films. U conductor. U The joining compound used in aluminium connectors UU While making a straight twist joint, the twisted portion prevents or retards reformation of the oxide. should contain about six turns. UU While replacing aluminium wires instead of copper UU PVC insulated aluminium cable 7/3 indicates that the wires in conduits, it is necessary to verify the size of cables have seven conductors and the diameter of each the conduits as aluminium cables are thicker than conductor is of 3 mm. copper. UU The mechanical strength of an aluminium cable is less UU The bending angle of the hard drawn bare copper than that of copper cables. conductor for a Britannia joint should be 90°. UU Normally, aluminium cables are indicated by their UU The bending angle of the annealed copper wire for diameter in millimeter rather than standard wire gauge Britannia joint should be 180°. numbers. UU A Britannia joint is used in O.H. lines. A Handbook on Electronics 9 UU A Britannia straight joint is used to increase the length UU In a LC coupled amplifier, the component used as of the conductor. collector load is inductor/choke. UU The correct size of binding wire for a Britannia joint UU The advantage of using a choke in coupling circuits having No. 6 SWG conductor is 18 SWG. is, its low dc resistance but high ac resistance. UU The overlapping distance of conductors for a Britannia UU The most common method of coupling used in AF joint should be 20-25 times the diameter of the conductor amplifiers is R-C coupling. to have good mechanical strength and electrical UU The advantage of using a choke as the collector conductivity. load in a LC coupled amplifier is, its low dc resis- UU The Britannia joint is well suited for copper conductors tance but high ac impedance. used in earth connection and short span distribution UU In a series regulator the line current remains constant lines. for a constant load current and constant input voltage. UU Soldering of a Britannia joint is a necessity to avoid UU In a series regulator the line current is equal to laod loosening of the joint due to vibrations and change in current + reference element current. atmospheric temperature. UU In a series regulator the series element is the transis- UU An annealed copper Britannia joint .requires a complete tor. bend to withstand tensile stress. UU The power wastage in a series-pass transistor is equal UU Short span distribution lines are the ones having less to the difference of input and output power. than 80 meter distance between adjacent poles. UU The series-pass transistor requires a heat sink when the UU While making Britannia joint, hold the conductors power wastage in the transistor is more than 500 mW. together with Hand vice. UU The value of maximum zener current is obtained UU To straighten the conductor, use a mallet. Zener wattage from . UU A perfect joint should possess good electrical conductivity Zener voltage and mechanical strength. U UU To clean the surface to be joined in conductor use zero U In a single Zener diode and transistor regulator, what is sandpaper. the relation between zener diode current and load current UU An annealed copper conductor could be bent easily. for a given input voltage? (Zener diode current UU Conductivity of copper is more than that of alumini- decreases as the load current increases) U um. U In a feedback voltage regulator, the error voltage is UU The weight of aluminium is less than that of copper. derived from the voltage divider at output. U UU The mechanical strength of copper is more than that of U The preset is a feedback voltage regulator is used to aluminium. vary output voltage. U UU For binding a 4 mm Britannia joint 0.914 mm tinned U An SCR can be tested for its condition with an copper conductor is used. ohmmeter. U UU For bending the copper conductor combination plier is U The voltage across anode to cathode of an SCR after it used. has been fired will be between 0.7 to 1 V. U UU A crystal develops emf when compression or ex- U The forward current IF in a non fired SCR is zero current. pansion takes place. UU In SCR used rectifier circuits, the current flow depends UU Among the various types of crystals the ‘Quartz’ crystals upon the conduction angle and the load. is widely used. The reason is that it is almost perfectly UU The angle of conduction is the output of a half wave elastic. controlled rectifier is zero. UU Of crystal resonance frequency is, say, 4.43361875 UU In SCR circuits when resistance and reactance trigger- MHz then the oscillator frequency is same as the ing methods are employed the conduction angle can crystal frequency. be between 00 to 180°. UU The output of Colpitt’s oscillator is a sine wave. U UU When a crystal is subjected to mechanical stress and U The most common method of triggering a industrial strain, an emf is induced in the crystal. This is known control circuit is gate triggering SCR. U as piezo electric effect. U In SCR circuits when resistance triggering method UU The problem of frequency drift in a Colpitt’s oscil- is used, the conduction angle cannot exceed 90° lator can be largely overcome by using high ‘Q’ UU How are SCRs normally turned on? coils and good quality capacitors. (By applying gate current) UU Piezo electric crystal is used in a gramophone pick UU What happens to the value of forward breakover voltage up unit and gas lighter. required to turn on an SCR as more gate current is UU Colpitt’s oscillators are used for generating frequencies applied? (It decreases) above 1 MHz. UU An SCR is a semi-conductor device. UU In RC coupled amplifiers, the drop in gain at low UU After an SCR is triggered, it continues to conduct until frequencies is due to capacitive reactance. power is lost in the circuit. 10 A Handbook on Electronics UU A single SCR in an ac circuit acts like a half-wave UU The potential difference that causes the breakdown of rectifier. insulation is called the breakdown voltage. UU How many pulses are required to turn an SCR on and UU Varnished cambric tape is best for use on motor off in a dc circuit. (Two) connections. UU In an ac circuit, an SCR conducts during one half of the UU If you are stripping cable insulation with a knife, you cycle only. must not cut/nick/shave the wire and weaken it. UU How can you increase the amount of power delivered UU Once cut, pull the insulation of the cable, using hand or by an SCR in an ac circuit? pliers. (Turn it on earlier in the cycle) UU The numbers marked in the manual wire stripper UU An SCR does Not have a choke. indicate SWG. UU UJT can be used as a relaxation oscillator due to UU The wire stripper has a series of holes as well in it its Negative resistance characteristic. scissors blade to allow stripping of cables of different UU Frequency of oscillation produced in a UJT based sizes. 1 UU To prevent cutting of the wire and weaken it, the opening relaxation oscillator could be found by . REC in the wire stripper must be equal to gauge size of UU A Western union joint is used to extend/increase the wire. length of the conductor on a overhead line. UU If the wire is placed in an oversized opening, it will not UU For making a Western union joint Hand vice should be cut fully the insulation completely. used to hold the wire ends, and to avoid knicks we have UU An electrical insulating material does not lose electron to use aluminium sheets between the jaws. under normal working conditions.. UU To clean the copper conductor at the place of joining, UU Non-conducting materials are called dielectrics as well we have to use double zero sandpaper. as insulators. UU Married joints are made in the cable to extend /increase UU A common measure of wire diameter is the gauge the length of run. number. UU After repeated melting of the solder, it is necessary to UU Wires and cables can be classified according to the kind compensate the loss by adding tin to the solder. of covering they have. UU The objective of the small zinc contents in aluminium UU A cable consists of two or more conductors inside a solder is to facilitate alloying of the solder with single covering. aluminium. UU The amount of potential difference, a layer of insulation UU Soft solders are alloys which have a melting point below can withstand without breaking down is called 300°C. breakdown voltage. UU Before soldering a lug to a cable we have to tin the lug UU Side cutting pliers are also called as Nipper pliers or and the conductor. Diagonal cutting pliers. UU In soldering aluminium cables with a ferrule joint it is UU Four uses of side cutting pliers are advisable to use a copper ferrule. 1. Cutting small conductors close to terminals. UU The melting point of 60% tin 40% lead solder is 2. Remove cable covering. 185°C. 3. Splitting and removing cottor pins. UU The melting point of aluminium solder is 170°C – 4. Cutting small wires and cables into pieces. 215°C. UU Two sizes of side cutting pliers are side cutting pliers UU A resin-cored solder can be used in the soldering process and combination pliers. without using flux. UU Side cutting plier with an insulated handle is used by UU The main purpose of the soldering flux is De- electricians. oxidising. UU High quality rubber or plastic is used as insulating UU Organic fluxes used for aluminium soldering will char material for handles of pliers used by electricians. if exposed to temperatures beyond 300°C UU Slice an insulation using a knife at an angle of 20 degrees UU The fluxes used for soldering electrical conductors must with the axis of the cable to avoid cutting/shaving into be free from acid. the conductor. UU Before soldering a joint, the joint has to be first cleaned UU The ideal solder for electrical soldering contains 60% and then tinned. tin and 40% lead. UU The cutting edge of an electrician knife, when sharp UU If the termination is not tight enough heat will be will not appear even as a thin line. produced at the terminal. UU Porcelain material is not a good conductor. UU Any type of termination, if improperly carried out, will UU A wire measuring one mm diameter has a cross-sectional lead to heating the terminating points and cables, short area of 9.78 mm2. circuits, earth leakage. A Handbook on Electronics 11

Practice Exercise

1. If the cumulative distribution function is Fx(x), then Codes: the probability density function fx(x) is given as: A B C (a) 1 2 3 (a) Fxx ()dx (b) d/dx Fx(x) ∫ (b) 4 3 2 Fx()− dx (c) ∫ x (d) d/dx Fx (– x) (c) 2 3 4 2. The maximum power that a 12 V d.c. source with (d) 2 5 3 an internal resistance of 2 Ω can supply to a 6. In the graph shown in the figure, one possible tree is resistive load is: formed by the branches 4, 5, 6, 7: (a) 12 W (b) 18 W 8 (c) 36 W (d) 48 W 6 7 3. Consider the following statements associated with the superposition theorem: 1. It is applicable to d.c. circuits only 3 4 2. It can be used to determine the current in a branch 1 2 or voltage across a branch 3. It is applicable to networks consisting of more 5 than one source Then one possible fundamental loop is: 4. It is applicable to networks consisting of linear (a) 1, 4, 5 (b) 2, 3, 5 and bilateral elements (c) 3, 4, 8 (d) 6, 7, 8 Which of these statements are correct? 7. Which of the following statements is not a property (a) 1, 2 and 3 (b) 2, 3 and 4 of R-L driving point impedance? (c) 3, 4 and 1 (d) 4, 1 and 2 (a) The first critical frequency at the origin is zero 2 2 4. The Fourier transform of e−πt is e−πf ; then the (b) The last critical frequency is a pole 2 Fourier transform of e−αt is: (c) The impedance at S = ∞ is always less than the π22f impedance at S = zero π −  1  −αf 2 e α (d) The slope of the impedance curve is positive at (a)   e (b) α  α  all points

f 2 8. In a network containing resistances and reactances 1 −π22f − (c) e (d) πα e πα2 the roots of the characteristic equation give for the πα circuit: 5. Figure given below shows a graph with 6 vertices and (a) the force response 8 edges. (b) the total response 7’ (c) the natural response (d) the damped response 6’ 8’ 9. A series RL circuit is initially relaxed. A step voltage is applied to the circuit. If τ is the time constant of 5’ 4’ the circuit, the voltage across R and L will be the same 1’ 3’ at time t equal to: 2’ (a) τln 2 (b) τln (1/2) (c) 1/τ ln 2 (d) 1/τ (1/2) With reference to the above graph, match List I with 10. For the following circuit a source of V (t) = e–2t is List II and select the correct answer: 1 applied. List I A. Fundamental circuit of chord 6′ 1 Ω B. Fundamental circuit of chord 7′ C. Fundamental circuit of chord 8′ 1 F List II V1(t) V2(t) 1. The edge set (1′, 2′, 4′, 6′)

2. The edge set (2′, 4′, 5′, 7′) 3. The edge set (2′, 3′, 5′, 8′) Then the resulting response v2(t) is given by: 4. The edge set (1′, 2′, 4′, 7′) (a e–2t + e–t (b) e–t 5. The edge set cannot be determined (c) e–t – e–2t (d) e–2t/2 12 A Handbook on Electronics t = 0 ′ 11. 15. A network N is a dual of network N if: + (a) both of them have same mesh equations 10 Ω R + (b) both of them have the same node equations 2 h 0.5 V V (c) mesh equations of one are the node equations of – V – the other (d) KCL and KVL equations are the same The time constant of the circuit after the switch shown 16. An element used in whose atoms in the figure is opened is: have three valence electrons is: (a) 0.2 s (a) germanium (b) silicon (b) 5 s (c) a donor (d) an acceptor (c) 0.1 s 17. In a semiconductor, the movement of holes is due (d) dependent on R and hence cannot be determined to: unless R is known (a) movement of electrons in conduction band 12. Match List I with List II and select the correct answer: (b) movement of holes in conduction band List I (c) movement of electrons in valence band A. A series RLC circuit is overdamped when (d) movement of holes in valence band. B. The unit of the real part of the complex 18. In an intrinsic semiconductor: frequency is (a) the number of holes is too small C. If F(s) is the Laplace transform of f(t) then F(s) (b) there are no holes in the material and f(t) are known as (c) electrons in the material are neutralized by D. If f(t) and its first derivative are Laplace holes transferable then the initial value of f(t) is given (d) there are no electrons in the material. by 19. For converting intrinsic semiconductor into N-type extrinsic semiconductor, which of the following List II doping elements would not be suitable: 1. f(t) = sF(s) (a) phosphorous (b) indium → → ∞ lim t 0 lim s (c) arsenic (d) antimony 2 2 2. R /4L < 1/LC 20. In the energy band diagram of a P-type semiconduc- 3. rad/s tor: 4. inverse functions (a) the acceptor hand is near the valence band 2 5. R /4L > 1/LC (b) the acceptor band is near the conduction band 6. neper sec–1 (c) the donor band is near the valence band 7. f(t) = sF(s) (d) the donor band is near the conduction band. lim t → 0 lim s → 0 Directions (Q. 21-26): The following questions 8. transform pairs consist of two statements, one labelled as ‘Assertion A’ and Codes: the other labelled as ‘Reason R’. You are to examine these A B C D two statements carefully and decide if the Assertion A and (a) 5 6 8 1 the Reason R are individually true and if so, whether the (b) 5 6 1 8 Reason is a correct explanation of the given Assertion. (c) 6 5 3 4 Select your answers to these items using the codes given below and mark your answer sheet accordingly. (d) 6 5 2 7 (a) Both A and R are true & R is the correct explana- 13. Consider the following: tion of A Energy storage capability of basic passive elements (b) Both A and R are true but R is not the correct is due to the fact that explanation of A. 1. resistance dissipates energy (c) A is true but R is false 2. capacitance stores energy (d) A is false but R is true 3. inductance dissipates energy 21. Assertion (A) : When a sinusoidal voltage is switched Which of the above is/are correct? on to a circuit consisting of R-L-C elements, the (a) 1, 2 and 3 (b) 1 and 3 response consists of two components expressed by (c) 3 alone (d) 1 and 2 free response and force response. L Reasons (R) : The response at t = 0+ is called free 14. has the dimension of : response as the voltage was just then switched and C the one at t = very large is forced response as it (a) time (b) capacitance consists of values of R, L, C applied voltage and its (c) inductance (d) resistance frequency. A Handbook On Electronics [For Railway & Other Engineering (Diploma) Competitive Examinations]

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