InterviewSolution
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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 151. |
A Zener of power rating 1 W is to be used as a voltage regulator. If Zener has breakdown of 5 V and it has to regulate voltage which flucated between 3V and 7V , what should be the value of R for the safe operation. ` |
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Answer» Power rating, `P=1W, V_(z)=5V,R_(s)=?, V_(s)=3V "to" 7V` `I_(z_(max))=P/V_(z)=1/5=0.2A, R_(s)=(V_(s)-V_(z))/I_(z_(max))=(7-5)/0.2=10Omega` |
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| 152. |
What is the output y for a gate, when `y=bar(bar(A.B))`? |
| Answer» `y=bar(bar(A.B))=A.B`. It represents AND gate. | |
| 153. |
Why is the conductivity of n-type semiconductor greater than that of the p-type semiconductor even when both of these have the same level of doping? |
| Answer» It is because, under a given electric field, the mobility of electron is higher than that of hole. | |
| 154. |
Differentiate between three segment of a transistor on the basis of their size and level of doping. |
| Answer» Emitter is of moderate size and heavily doped. Base is very thin and lightly doped, collector is moderately doped and of larger in size. | |
| 155. |
Write the function of three segments of a transistor. |
| Answer» The function of emitter is to emit the majority carriers. Function of collector is to collect the majority carriers coming from emitter through base. Base provides the proper interaction between the emitter and the collector. | |
| 156. |
In a transistor, forward bias voltage is always low as compared to reverse bias voltage. Why? |
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Answer» In a transistor, emitter-base junction is forward biased with low voltage battery and collector-base junction is reverse biased with high voltage battery. If forward bias voltage is made large, the majority carriers in emitter will drift towards the collector through base region with large velocity. Since their number is also large, a large heat is produced which breaks up the covalent bonds and the transistor gets spoiled. However, if the reverse bias voltage applied to collector is large, it simply collects the majority carriers easily, comimg from emitter through base, but no heating effect is produced nor breaking of covalent bond takes place in transistor. |
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| 157. |
In a common emitter transistor circuit, a bulb B and a volmeter V are connected as shown in Fig.What change would take place in bulb B and volmeter V when the value of resistance R is increased? |
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Answer» When the value of resistance R is increased, the current in the input circuit decreases and heance emitter current `I_(e)` decreases. Due to it, the collector current `I_c (=I_(e)-I_b)` decreases. As a result of it, the bulb B glows dim. The decrease in the input current can be interpreted as the decrease in the base emitter volltage `(V_(BE))`. If V is the voltage across the collector-base circuit then in a closed circuit. `V_(C C)=V+V_(BE)` or `V=V_(C C)-V_(BE)` When `V_(BE)` decreases V increases. It means voltage will show higher voltage. |
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| 158. |
In the circuit shown , a switch which is open represents the logic state 0 and the switch which is closed represents the logic state 1. The lampL is lit when output is logic state 1. What type of gates are represented by the circuits in (i) and (ii) of Fig. |
| Answer» (i) AND gate (ii) OR gate | |
| 159. |
Out of the transistors n-p-n and p-n-p which one is more commonly used and why? |
| Answer» n-p-n transistor is more commonly used than p-n-p transistor. Because in n-p-n transistor electrons are the main charge carriers while in p-n-p transistor holes are the main charge carriers. The mobility of electrons is much higher than those of holes. | |
| 160. |
Under what condition a transistor works as an open switch? |
| Answer» A transistor will work as an open switch in the cut off state i.e., when both the emitter and collector are reversed biased. | |
| 161. |
How is a transistor biased to be in active state? |
| Answer» Transistor is said to be in active state when its emitter-base junction is suitably forward biased and base-collector junction is suitably reverse biased. | |
| 162. |
What is the condition for the state of saturation of a transistor? |
| Answer» The transistor is in saturation state if `I_bbeta_(a.c.) gt =I_c`. In this condition, during the positive half cycle of a.c. signal, the current `I_b` increases resulting an increasing in `I_c`, which is so large that `V_(CE)` become less than `V_(BE)`. Due to it, the transistor goes into saturation state and no longer works as an amplifier. | |
| 163. |
In n-p-n transistor, what are the current carriers inside and outside the transistor circuit? |
| Answer» Electron are the current carriers through the transistor and in the external circuit. | |
| 164. |
Three amplifier circuit are connected in series. The voltage gain of each is 5. What is the final voltage amplification? |
| Answer» Final voltage amplification`=5xx5xx5=125`. | |
| 165. |
Power gain of transistor amplifier with common base circuit or common emitter circuit is large. Does it mean the power is generated by the transistor? Explain. |
| Answer» No, the transistor is not generating the power. The energy for the higher a.c. power t the output is being supplied by the d.c. battery. | |
| 166. |
What is feed back? |
| Answer» Feed back is a process in which a part of the output singal is supplied back to the input signal. | |
| 167. |
In p-n-p transistor, what are the current carriers inside and output the transistor circuit? |
| Answer» Holes are the current carriers through the transistor but the electrons are the current carriers in the external circuit. | |
| 168. |
When a transistor is used as an oscillator, why is it necessary to feed back energy to L-C circuit? |
| Answer» This is done in order to compensate for loss of energy due to resistsnce in L-C oscillatory circuit and hence to produce undamped electromagnetic waves or carriers waves. | |
| 169. |
What do you understand by (i) positive feed back and (ii) negative feed back? |
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Answer» (i) The positive feed back is that process in which the feed back from the output signal is in phase with the input signal. (ii) The negative feed back is that process in which the feed back from the output signal is in phase with the input signal |
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| 170. |
Would you prefer to use a transistor as a common base or a common emitter amplifier? |
| Answer» A common emitter transistor amplifier is preferred when we require better current gain and power gain. But common base transistor amplifier is preferred when we require better voltage gain without any phase change of singnal voltage. | |
| 171. |
What type of feed back is required in an oscillator? |
| Answer» Correct Answer - Positive feed back | |
| 172. |
The comdination of gates shown below yields A. NOT gateB. XOR gateC. NAND gateD. OR gate |
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Answer» Correct Answer - D The Boolean expression of these gates is `X=bar(barA.barB)=bar(barA)+bar(barB)=A+B` It means OR gate is formed. |
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| 173. |
Derive a relation between current gain of common emitter amplifier. |
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Answer» For a junction transistor, we know `I_(e)=I_b+I_c` ...(i) Current gain for common base amplifier, `alpha=I_c//I_(e)` Current gain for common emitter amplifier, `beta=I_c//I_b` From(i), `I_(e)/I_c=I_b/I_c+1` or `1/alpha=1/beta+1` or `1/beta=1/alpha-1=(1-alpha)/alpha` or `beta=alpha/(1-alpha)` |
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| 174. |
State the relation for the voltage gain in terms of trans-conductance, using transistor as an amplifier. |
| Answer» Voltage gain = - trans-conductance `xx` output resistance | |
| 175. |
In an n-p-n transistor circuit, the collector current ia 10 mA. If 90% of the electrons emitted reach the collector.A. the emitter current will be 9 mAB. the base current will be 1 mAC. the emitter current will be 11 mAD. the base current will be -1 mA |
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Answer» Correct Answer - B::C Here, `I_(C)=90/100I_(E)=0.91I_(E)`, `:. I_(E)=I_C/0.9=(10 mA)/0.9=11 mA` `I_B=I_(E)-I_C=11 mA-10 mA=1 mA` |
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| 176. |
In an n-p-n transistor circuit, the collector current is 9 mA. If 90% of the electrons emitter reach the collector, find the base current and collector current. |
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Answer» `I_c=90%I_(e)=90/100xxI_(e)` or `I_(e)=(100I_c)/90=(100xx9)/90=10mA` `I_b=10%I_(e)=10/100xx10=1mA` |
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| 177. |
In a normal operation of a transistor,A. the base-collector junction is forward biasedB. the base-collector junction is reverse biasedC. the base-emitter junction is forward biasedD. the base-emitter junction is reverse biased |
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Answer» Correct Answer - B::C In a normal working of a transistor, the emitter base junction is forward biased and collector base junction is reverse biased. |
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| 178. |
The electrical conductivity of pure silicon can be increased byA. increasing the temperatureB. doping donor impuritiesC. doping acceptor impuritiesD. falling ultraviolet light on it |
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Answer» Correct Answer - A::B::C::D The electrical conductivity of pure silicon can be increased by increasing the number of current carriers. Which can be done by incresing the temperature, or by doping donor impurities, or acceptor impurities, or by falling ultraviolet light on it. |
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| 179. |
In an n-p-n circuit transistor, the collector current is 10 mA. If 80% electrons emitted reach the collector, thenA. the emitter current will be 7.5 mAB. the emitter current will be 12.5 mAC. the base current will be 3.5 mAD. the base current will be 2.5 mA |
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Answer» Correct Answer - B::D Here, `I_(c)=80% of I_(e)=80/100I_(e)=0.8I_(e)` or `I_(e)=I_c/0.8=10/0.8=12.5 mA` `I_b=I_(e)-I_c=12.5-10=2.5 mA` |
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| 180. |
The conductivity of a semiconductor increases with increase in temperature becauseA. number density of free current carriers increasesB. relaxation time increasesC. both number density of carriers and relaxation time increaseD. number density of current carriers increases, relaxation time decreases but effect of decrease in relaxation time is much less than increase in number density |
| Answer» Correct Answer - D | |
| 181. |
Hole isA. an anti-partical of electronB. a vacancy created when an electron leavels a convalent bondC. absence of free alectronsD. an artifically created partical |
| Answer» Correct Answer - B | |
| 182. |
In the depletion region of a diode.A. there no mobile chargesB. equal number of holes and electrons exist, making the region neutralC. recombination of holes and electrons has taken placeD. immobile charged ions exit |
| Answer» Correct Answer - A::B::D | |
| 183. |
Identify the semiconductor device where characteristics are given below, in the order (i), (ii) (iii), (iv): A. simple diode, zener diode, solar cell, light dependent resistanceB. zener diode, simple diode, light dependent resistance, solar cellC. solar cell, light dependent resistance zener diode, simple diodeD. zener diode, solar cell simple diode light dependent resistance |
| Answer» Correct Answer - A | |
| 184. |
For transistor amplifier, the voltage gainA. remains constant for all frequenciesB. is high and low frequencies and constant in the middle frequency rangeC. is low at high and low frequencies and constant in the mid frequenciesD. None of the above. |
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Answer» Correct Answer - C the voltage gain is low at high and low frequencies and constant and high at mid-frequencies. |
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| 185. |
For transistor action, which of the following statements are correct ?A. collector current is equal to the sum of base current and emitter currentB. The input resistance depends upon the current `I_` in the transistor.C. The emitter junction is forward biased and collector junction is reverse biased.D. Both the emitter junction as well as the collector junction are forward biased. |
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Answer» Correct Answer - B::C for a transistor, `beta=I_c/I_B or I_B=I_c/beta`. `R_(i)=V_(i)/I_B=V_(i)/I_cbeta`, i.e., `R_(i)prop1/I_c`. Therefore,` R_(i)` depends upon collector current `I_c`. For a transistor action, the emitter junction is forward biased and collector junction is reverse biased. |
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| 186. |
When a forward bias is applied to a p -n junction. ItA. raises the potential barrierB. reduces the majority carrier current to zeroC. lower the potential barrierD. none of the above. |
| Answer» When a forward bias is applied across the p-n junction the applied voltage opposes the barrier voltage. Due to it, the potential barrier across the junction is lowered. Hence | |
| 187. |
The resistance of an intrisic semiconductor when heatedA. increasesB. remains constantC. decreases linearlyD. decreases exponentially |
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Answer» Correct Answer - D The resistance of an intrinsic semiconductor decreases exponentially with the rise in temperature, as for semiconductor `R prop e^(-E_(g)//2kT`. |
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| 188. |
What is fermi level and fermi energy? |
| Answer» In an energy band, the highest energy level occupied by electron at 0K is called fermi level and its energy is called fermi-energy. | |
| 189. |
Fig, shows a logic gate circuit with two input A and B and the output C. The voltage wave form of A, B and C are as shown in Fig.The logic gate circuit is A. OR gateB. AND gateC. NOR gateD. NAND gate |
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Answer» Correct Answer - D Since the output `C` is at level `0` when both the inputs `A` and `B` are of level `1` and output is `1` when both the inputs are `0, 0` or `0, 1` and `1, 0`. Hence the logic circuit gate is NAND gate. |
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| 190. |
If the forward bias on p-n junction is increased from zero to 0.05V, then no current in the circuit flows. What is the contact potential of junction diode? |
| Answer» Correct Answer - `0.05V`. | |
| 191. |
The breakdown in a reverse biased p-n junction diode is more likely to occur due toA. large velocity of the minority charge carriers if the doping concentration is smallB. large velocity of the minority charge carriers if the doping concentration is largeC. strong electric field in a depletion region if the doping concentration is smallD. strong electric field in the depletion region if the doping concentration is large |
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Answer» Correct Answer - A::D In reverse biasing, the minority charge carriers will be accelerated due to reverse biased, which on striking with atoms cause ionisation resulting secondary electrons and thus more number of charge carriers. When doping concentration is large, there will be large number of ions in the depletion region, which will give rise to a strong electric field. |
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| 192. |
The output of an AND gate assumes 1 (in level) if ...........inputs assume 1(in level) |
| Answer» Correct Answer - all the | |
| 193. |
Sketch the output y from a NOR gate having input A and B as given in Fig. |
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Answer» For NOR gate the Boolean expression is `bar(A+B)=y` For the given wave form, we have the following value for A, B and y. For time `t lt t_(1), A=1, B=1` hencey `=0` For time `t_(1) "to" t_(2), A=0, B=0` hencey `=1` For time `t_(2) "to" t_(3), A=0, B=1` hencey `=0` For time `t_(3) "to" t_(4), A=1, B=0` hencey `=0` For time `t_(4) "to" t_(5), A=1, B=1` hencey `=0` For time `t_(5) "to" t_(6), A=0, B=0` hencey `=1` For time `t gt t_(6), A=0, B=1` hencey `=0` The wave from for output y is as shown in Fig. |
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| 194. |
What is zener breakdown? |
| Answer» When a very large reverse voltage is applied across a p-n junction, so that there is a sudden large reverse current flowing through p-n junction. Then the effect is called zener breakdown. | |
| 195. |
What is the ratio of forward and reverse resistance of p-n junction diode? |
| Answer» Correct Answer - `10^(-4) : 1`. | |
| 196. |
According to energy band diagram, what makes a substance conductor insulator? |
| Answer» Overlapping of conductor band and valence band A large energy gap (more than 3eV) between conduction band and valence band. | |
| 197. |
The output of an unregulated dc power supply is to be regulated. Name the device that can be used for this purpose. |
| Answer» Zener diode is used to regulation the output of an unregulated dc supply. | |
| 198. |
Why are photodiodes used preferably in reverse bias condition? |
| Answer» In reverse bias condition of photodiode, the change in saturation reverse current is directly proportional to the change in the incident light flux or light intensity, which can be measured accurately. It is not so when photodiode is forward biased. | |
| 199. |
What is solar cell? |
| Answer» It is a p-n junction device which converts solar energy into electrical energy. | |
| 200. |
The forward biased diode connection isA. B. C. D. |
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Answer» Correct Answer - C For forward biasing p-type of p-n junction should be at higher potential than n-side of junction. |
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