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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.
| 451. |
The concertration of hole-electron pairs in pire silicon at `T=300K` is `7xx10^(15` per cubic metre. Antimoy is doped into silicon in a proportion of `1` arom in `10^(7)` atoms. Assuming that half of the inpurity atoms contribute electrons in the conduction band, calculate the factor electrons in the conduction band, calculate the factor by which the number of charge carriers increase due to doping. the number of silicon atoms per cubic meter is `5xx10^(28)`. |
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Answer» `n_(i)7xx10^(15)//m^(3)` `N_(D)=(5xx10^(28))/(10^(7))=5xx10^(21)//m^(3)` Half of impurity atoms contribute electrons. Before doping, number of charge carries `=2xx7xx10^(15)` `=14xx10^(15)//m^(3)` After doping, number of charge carries `=(N_(D))/(2)+14xx10^(15)` `=2.5xx10^(21)+14xx10^(15)=2.5xx10^(21)` the factor by which the number of charge carries is increased `=(2.5xx10^(21))/(14xx10^(15))=1.8xx10^(5)` |
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| 452. |
Determine the number of density of donor atoms which have to be added to an intrisic germanium semiconductor to produce an `n`-type semiconductor of conductivity `5mho//cm`. Given that the mobility of electrons in `n`-type semiconductor is `3850cm^(2)//volt-sec`. |
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Answer» Assuming `N_(D)=n_(e)` `sigma=n_(e)emu_(e)` `5xx10^(2)=n_(e)xx1.6xx10^(-19)xx3850xx10^(-4)` `n_(e)8.1xx10^(21)//m^(3)` |
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| 453. |
When light falls on a photo diode, its conductivity increases. Experimetally it is found that the conductivity changes only when the wavelength of the incident light is less than 620 nm. The band gap of the diode isA. 0.75 eVB. 1.1 eVC. 1.5 eVD. 2.0 eV |
| Answer» Correct Answer - D | |
| 454. |
A forward biased diode isA. B. C. D. |
| Answer» Correct Answer - D | |
| 455. |
A photocell employs photoelectric effect to convertA. change in the frequency of light into a change in electric voltageB. change in the intensity of illumination into a change in photoelectric currentC. Change in the intensity of illumination into a change in the work function of the photocathode.D. change in the freqauency of light into a change in the electric current. |
| Answer» Correct Answer - 2 | |
| 456. |
Four silicon diodes are connected as shown in the figure. Assuming the diodes to be ideal. The current through the resistor R is A. 0.2 AB. 0.1 AC. 0.3 AD. 0.5 A |
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Answer» Correct Answer - B `I=(V)/(R)=(6)/(250+50)=0.02A` |
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| 457. |
In the circuit shown below D1 and D2 are two silicon diodes. The current in the circuit is …………….(A) 2 A (B) 2 mA (C) 0.8 mA (D) very small (approx 0) |
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Answer» (D) very small (approx 0) |
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| 458. |
Which one of the following is the correct statement regarding the depletion region of an unbiased p-n junction?A. Its width does not depend upon the densities of the impurities (dopants)B. Its width is considerably increased when it is forward biasedC. The electric field in the depletion region is produd by the electrons in the conduction band and holes in the valence bandD. The potential barrier across the junction produces a very strong electric field |
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Answer» Correct Answer - D (a),(b) , (c ) is wrong. (d) is the corrent statement . e.g. For Ge, dV=0.3 V and dx = `10^(-6)` m `therefore E="dV"/"dx" = 0.3/10^(-6) = 0.3xx10^6 = 3xx10^5` V/m Thus a strong electric field is produced. |
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| 459. |
For p-n junction in reverse bias, which of the following is true? (A) There is no current through P-N junction due to majority carriers from both regions. (B) Width of potential barriers is small and it offers low resistance. (C) Current is due to majority carriers. (D) Both (B) and (C) |
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Answer» (A) There is no current through P-N junction due to majority carriers from both regions. |
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| 460. |
If a p-n junction diode is not connected to any circuit, then (A) the potential is same everywhere. (B) potential is not same and n-type side has lower potential than p-type side. (C) there is an electric field at junction direction from p-type side to n-type side. (D) there is an electric field at the junction directed from n-type side to p-type side. |
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Answer» (D) there is an electric field at the junction directed from n-type side to p-type side. |
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| 461. |
In the figure, the input is across the terminals A and C and the output is across B and D. Then the output is (a ) zero ( b) same as the input ( c) full - wave rectified (d) half - wave rectified .A. zeroB. same as inputC. full wave rectifiedD. half wave rectified |
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Answer» Correct Answer - B Circuit will act as full wave rectifier |
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| 462. |
The width of depletion region …………… (A) becomes small in forward bias of diode (B) becomes large in forward bias of diode (C) is not affected upon by the bias (D) becomes small in reverse bias of diode |
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Answer» (A) becomes small in forward bias of diode |
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| 463. |
Graph of position of image vs position of point object from a convex lens is shown. Then, focal length of the lens is A. `0.50+-0.05cm`B. `0.50+-0.10cm`C. `5.00+-0.05cm`D. `5.00+-0.10cm` |
| Answer» Correct Answer - C | |
| 464. |
In the figure, the input is across the terminals A and C and the output is across B and D. Then the output is (a ) zero ( b) same as the input ( c) full - wave rectified (d) half - wave rectified .A. zeroB. same as inputC. full wave rectifiedD. half wave rectified |
| Answer» Correct Answer - C | |
| 465. |
A galvanometer is connected as shown in figure. It has resistance `100Omega`. What should be the resistance connected to it in parallel so that its deflection is reduced to half?A. `100Omega`B. `99Omega`C. `91Omega`D. `90Omega` |
| Answer» Correct Answer - C | |
| 466. |
The focal length of a convex mirror is obtained by using a convex lens. The following observation are recorded during the experiment- `{:("object position",=5cm),("Image",=93.8cm),("Mirror",=63.3cm),("Bench error",=-0.1cm):}` Then the focal length of mirror will beA. 7.5 cmB. 8.4 cmC. 15.3 cmD. none of these |
| Answer» Correct Answer - C | |
| 467. |
An oscillator is nothing but an amplifier withA. positive feedbackB. high gainC. no feed backD. negative feed back |
| Answer» Correct Answer - A | |
| 468. |
The output of the given logic gate is 1 when inputs A,B and C are such that :- A. `A=1,B=0,C=1`B. `A=1,B=1,C=0`C. `A=B=C=0`D. `A=B=C=1` |
| Answer» Correct Answer - D | |
| 469. |
Which of the following statements is falseA. The bench correction is always equal to the negative of bench errorB. larger the distance between the two object larger the magnitude of parallaxC. parallax disappear if the positions of two objects coincideD. parallax can occur between any two object |
| Answer» Correct Answer - B | |
| 470. |
Choose the only false statement form the followingA. the resistivity of a semiconductor increases with increase in temperatureB. substances with energy gap of the order of 10 eV are insulatorsC. in conductors the valence and conduction bands may over lapD. the conductivity of a semiconductor increases with increases in temperature |
| Answer» Correct Answer - A | |
| 471. |
An unknown transistor needs to be identified as `npn` and `pnp` type. A multimeter, wilth `+ve` and `-ve` terminals is used to measure resistance between different terminals transistor. If terminal `2` is the base of the transistor then which of the following is correct for a `pnp` transistor?A. `+ve` terminal `2,+ve` terminal 2, resistance highB. `+ve` terminal `1,-ve` terminal 2, resistance highC. `+ve` terminal `2,-ve` terminal 2, resistance lowD. `+ve` terminal `2,-ve` terminal 1, resistance high |
| Answer» Correct Answer - D | |
| 472. |
Which one of the following statements is false ?A. Pure Si doped with trivalent impurities gives a p-type semiconductorB. Majority carriers in a n-type semiconductor are holesC. Minority carriers in a p-type semiconductor are electronsD. The resistance of intrinsic semiconductor decreases with increase of temperature |
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Answer» Correct Answer - B p-type semiconductor are obtained by adding a small amount of trivalent impurity to a pure sample of semiconductor (Ge). Majority charge carriers-holes Minority charge carriers-electrons n-type semiconductor are obtained by adding a small amount of pentavalent impurity to a pure sample of semiconductor (Ge). Majority charge carriers-electrons The resistance of intrinsic semiconductors decreases with increase of temperature. |
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| 473. |
The ` 1- V` characteristic of on LED isA. B. C. D. |
| Answer» Correct Answer - A | |
| 474. |
The forward biased diode connection isA. B. C. D. |
| Answer» Correct Answer - C | |
| 475. |
The forward biased diode connection isA. B. C. D. |
| Answer» Correct Answer - A | |
| 476. |
The forward biased diode connection isA. B. C. D. |
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Answer» Correct Answer - A In forward biased diode connection p-side is at higher potenital and n-side is at lower potential. |
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| 477. |
An incomplete sentence about transistors is given below:The emitter-.....junction is - and the collector-..... junction is ..... .The appropriate words for the dotted empty positions are respectively.(a) ''collector'' and base'(b) ''base'' and emitter'(c) ''collector'' and emitter'(d) ''base'' and base. |
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Answer» (d) ''base'' and base. |
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| 478. |
Which of the following element is used in making transistors ?A. siliconB. CadmiumC. TungstenD. Molybdenum |
| Answer» Correct Answer - A | |
| 479. |
In the use of transistor as an amplifierA. emitter base junction is in forward biased and collector junction is reverse biased.B. biasing voltage are not requriedC. both junction are forward biasedD. both junction are reverse biased |
| Answer» Correct Answer - A | |
| 480. |
A `npn` transistor conducts whenA. Both collector and emitter are positive with respect to the base.B. Collector is positive and emitterl is negative with respect to the base.C. collector is positive and emitter is at same potential as the base.D. Both collector and emitter are negative with respect to the base. |
| Answer» Correct Answer - B | |
| 481. |
Which of the following is not the disadvantage of transistor over a triode ?A. Low efficiencyB. Higher efficiencyC. Higher noise levelD. Higher sensitivity |
| Answer» Correct Answer - A | |
| 482. |
A `npn` transistor conducts whenA. Slightly more than the collector currentB. Slightly less thanthe collector currentC. Equal to the collector currentD. Equal to the base current |
| Answer» Correct Answer - A | |
| 483. |
The main current, crossing the collector junction in a normally biased n-p-n transistor, isA. hole currentB. drift currentC. base currentD. diffusion current |
| Answer» Correct Answer - B | |
| 484. |
The electrical circuit used to get smooth `dc` output from a rectifier circuit is calledA. oscillatorB. full wave rectifierC. amplifierD. filter |
| Answer» Correct Answer - D | |
| 485. |
In a properly biased transistor-A. both depletion layers are equially large.B. both depletion layers are equally small.C. Emitter-base depletion layer is large but base collector depletion layer is small.D. Emitter-base depletion layer is small but base-collector depletion layer is large. |
| Answer» Correct Answer - D | |
| 486. |
The movement of a hole is brought about by the valency being filled by a ……………….. (A) free electrons (B) valence electrons (C) positive ions (D) negative ions |
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Answer» Correct option is: (B) valence electrons |
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| 487. |
The value of barrier potential of P-N juntion in Ge is-A. 0.03 volt in the direction of forward currentB. 0.3 volt in the direction opposite of the forward currentC. 25 volt in the direction opposite to the forward currentD. 25 volt in the direction of the forward current |
| Answer» Correct Answer - B | |
| 488. |
Druing P-N junction formation when the electron and holes stops moving from P to N and N to P, thenA. there is increase in number of `+ve` and `-ve` ions at junctionB. there is increase in number of electrons at junction.C. there is increase in number of holes at junctionD. there is increase in number of holes and electrons at junctions |
| Answer» Correct Answer - A | |
| 489. |
An amplifier has a voltage gain `A_(v)= 1000`. The voltage gain in `dB` is:A. 30B. 60C. 3D. 20 |
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Answer» Correct Answer - A Voltage gain, `A_(V)=1000` In dB, voltage gain `A=10log_(10)1000dB` `=(10xx3)log_(10)10dB` `=30dB " " (because log_(10)10=1)` |
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| 490. |
In a transistor, `I_(c)` = 20 mA, `I_(b)` =1 mA. What will be the value of `alpha` ?A. 20/21B. `1//20`C. 21/20D. 20 |
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Answer» Correct Answer - A `alpha=(I_(c))/(I_(e))=(I_(c))/(I_(e)+I_(b))=(20)/(20+1)=(20)/(21)` |
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| 491. |
What is the zener current in the following circuit ? A. 10 mAB. 15 mAC. 20 mAD. 25 mA |
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Answer» Correct Answer - B `R=(v_(i)-v_(0))/(I_(z)+I_(l))` `I_(z)+I_(l)=(150-50)/(5xx10^(3)) ` `I_(z)+I_(l)=20xx10^(-3)=20 mA` `therefore I_(z)=20-I_(l)` `=20-5=15` mA |
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| 492. |
In a transistor circuit, the emitter current is 50 mA and base current in 2 mA. The collector current isA. 25 mAB. 48 mAC. 100mAD. 552 mA |
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Answer» Correct Answer - B `I_(c)=I_(e)-I_(b)=50-2=48 mA` |
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| 493. |
What is the value of the output vot-tage `V_(0)` in the following ze-ner circuit ? A. 7 VB. 8 VC. 15 VD. 23 V |
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Answer» Correct Answer - B The output voltage is equal to voltage across zener diode because they are in parallel |
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| 494. |
Given below are four logic tage symboles. Those for `OR, NOR` and `NAND` are respectively: A. 1,4,3B. 4,1,2C. 1,3,4D. 4,2,1 |
| Answer» Correct Answer - C | |
| 495. |
In an n-p-n transistor circuit, the collector current is 20 mA. If 90 % of electron emitted reach the collector :-A. the emitter current will be 18 mAB. emitter current will be 22 mAC. base current will be 2mAD. base current will be 1mA |
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Answer» Correct Answer - B::C `I_(C)=90%I_(E)rArrI_(E)=(100)/(90)xxI_(C)=(100)/(90)xx20=22mA` `I_(B)=I_(E)=I_(C)=22-20=2mA` |
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| 496. |
Two identical p-n junctions may be connected in series with a battery in three ways (figure 45-Q1). The potential difference across the two p-n junctions are equal in(a) circuit1 and circuit2 (b) circuit2 and circuit3 (c) circuit3 and circuit1 (d) circuit1 only. |
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Answer» (b) circuit2 and circuit3 |
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| 497. |
Two identical p-n junctions may be connected in series in which a battery in three ways , fig . The potential drops across the two p - n junctions are equal in A. Circuit 1 and 2B. Circuti 2 and 3C. Circuit 3 and 1D. Circuit 1 only |
| Answer» Correct Answer - B | |
| 498. |
Carbon , silicon and germanium have four valence electrons each . At room temperature which one of the following statements is most appropriate ?A. the number of free conduction electrons is significant in C but small in Si and Ge.B. The number of free conduction electrons is negligibly small in all the three.C. the number of free electrons for conduction is significant in all the three.D. the number of free electrons for conduction is significant only in Si and Ge but small in C. |
| Answer» Correct Answer - D | |
| 499. |
Truth table for system of four `NAND` gates as shown in figure is : .A. `{:(A,B,Y),(0,0,0),(0,1,1),(1,0,1),(1,1,0):}`B. `{:(A,B,Y),(0,0,0),(0,1,0),(1,0,1),(1,1,1):}`C. `{:(A,B,Y),(0,0,1),(0,1,1),(1,0,0),(1,1,0):}`D. `{:(A,B,Y),(0,0,1),(0,1,0),(1,0,0),(1,1,1):}` |
| Answer» Correct Answer - A | |
| 500. |
For television broadcasting, the frequency employed is normallyA. 30-300 M HzB. 30-300 G HzC. 30-300 K HzD. 30-300 Hz |
| Answer» Correct Answer - A | |