22 + Interview Questions in The Operational Amplifier in Electric Circuits Page 1 InterviewSolution

1.	If the gain of aninverting amplifying circuit is 13 and ±22V power supplies are used. What range of input values allows the opamp to be in linear region?(a) ±1.69(b) ±1.35V(c) ±2.28(d) ±0.5I have been asked this question during an online exam.The question is from The Inverting and Non-Inverting Amplifier Circuit in division The Operational Amplifier of Electric Circuits
Answer» CORRECT choice is (a) ±1.69 To elaborate: GAIN= Rf/Rs= 13 and vo= (-Rf/Rs)*vs. → vo= -13vs and GIVEN -22V≤ vo ≤ 22V. → -22= -13vs. So, vs=1.692 V → 22=-13vs. So, vs=-1.692V.

Discussion

2.	The input applied to an Inverting amplifier is ______________(a) Equal to output(b) Equal to Inverted output(c) Not equal to output(d) Output is equal to inputI got this question during an interview.This key question is from The Inverting and Non-Inverting Amplifier Circuit topic in portion The Operational Amplifier of Electric Circuits
Answer» The CORRECT choice is (b) Equal to Inverted output To explain: The NAME itself indicates it is an INVERTING amplifier. So, the input applied is inverted and is GIVEN as output. SUPPOSE the input applied is sinusoidal then, the output is

Discussion

3.	If an inverting amplifying circuit has a gain of 10 and ±15V power supplies are used. The values of input for which opamp would be in the linear region?(a) ±1.25(b) ±1.5V(c) ±2.25(d) ±0.5I had been asked this question in quiz.The above asked question is from The Inverting and Non-Inverting Amplifier Circuit topic in division The Operational Amplifier of Electric Circuits
Answer» RIGHT option is (b) ±1.5V Best EXPLANATION: Gain= Rf/Rs= 10 and vo= (-Rf/Rs)*VS. → vo= -10vs and GIVEN -12V≤ vo ≤ 12V. → -15= -10vs. So, vs= 1.5V → 15=-10vs. So, vs=-1.5V.

Discussion

4.	If Rs= 5Ω, Rf= 25Ω and -2.5V ≤ vg ≤ 2.5V. What are the smallest power supply voltages that could be applied and still have opamp in linear region?(a) ±9V(b) ±2.5V(c) ±6V(d) ±15VI had been asked this question during an online exam.Asked question is from The Inverting and Non-Inverting Amplifier Circuit in section The Operational Amplifier of Electric Circuits
Answer» The correct option is (d) ±15V Explanation: vo= ((RS+Rf)/Rs) *VG. By SUBSTITUTING the values, we have vo=6vg. vo=6(-2.5) = -15 vo=6(2.5) =15.

Discussion

5.	If Rs= 3Ω, Rf= 6Ω then the relation between vo and vg in case of a Non-Inverting amplifying circuit.(a) vo= 9vg(b) vo= 6vg(c) vo= 3vg(d) vo= vgThis question was addressed to me in a job interview.Question is taken from The Inverting and Non-Inverting Amplifier Circuit in division The Operational Amplifier of Electric Circuits
Answer» The correct choice is (c) vo= 3vg To EXPLAIN I would say: vo= ((RS+Rf)/Rs) *vg.

Discussion

6.	The condition for a Non-inverting amplifying circuit to operate in linear region operation_____________(a) (Rs+Rf)/Rs < │VCC/vg│(b) (Rs+Rf)/Rs ≠ │VCC/vg│(c) (Rs+Rf)/Rs > │VCC/vg│(d) (Rs+Rf)/Rs = │VCC/vg│I got this question in quiz.The above asked question is from The Inverting and Non-Inverting Amplifier Circuit in section The Operational Amplifier of Electric Circuits
Answer» Right ANSWER is (a) (Rs+Rf)/Rs < │VCC/vg│ To explain: ASSUME that opamp is ideal. The CONDITION for the linear region OPERATION in a Non-inverting amplifying CIRCUIT is (Rs+Rf)/Rs <│VCC/vg│.

Discussion

7.	The circuits of an inverting and Non-Inverting amplifying comprises of __________ and _______ number of resistors.(a) 3, 2(b) 2, 3(c) 2, 2(d) 3, 3This question was posed to me in final exam.I'd like to ask this question from The Inverting and Non-Inverting Amplifier Circuit in division The Operational Amplifier of Electric Circuits
Answer» Right option is (B) 2, 3 Explanation: Inverting amplifying CIRCUIT- Rs, RF. Non-Inverting amplifying circuit – Rs, Rf, RG.

Discussion

8.	In the expression vo= -Avn, A is called ______________(a) Closed loop gain(b) Closed loop fault(c) Open loop fault(d) Open loop gainThe question was asked in an interview.My question is taken from The Inverting and Non-Inverting Amplifier Circuit in chapter The Operational Amplifier of Electric Circuits
Answer» CORRECT CHOICE is (d) OPEN loop gain The EXPLANATION is: A is CALLED open loop gain.

Discussion

9.	If VCC = 12V and vs=1mV, then Rf/Rsis _____________(a) >12000(b)
Answer» The correct CHOICE is (B) <12000 The BEST EXPLANATION: Rf/Rs≤ │VCC/vs│.

Discussion

10.	The other name for Gain is ____________(a) Scaling factor(b) Output(c) Amplifying factor(d) Scaling levelI had been asked this question in an online quiz.The above asked question is from The Inverting and Non-Inverting Amplifier Circuit topic in section The Operational Amplifier of Electric Circuits
Answer» Right option is (a) Scaling FACTOR Best EXPLANATION: The gain is also KNOWN as scaling factor and it is the ratio of Rf/Rs in case of an Inverting amplifying circuit.

Discussion

11.	In an Inverting Amplifier circuit, the output voltage vo is expressed as a function of ____________(a) Input current(b) Output current(c) Source voltage(d) Source currentI got this question in an online interview.Query is from The Inverting and Non-Inverting Amplifier Circuit in portion The Operational Amplifier of Electric Circuits
Answer» RIGHT choice is (c) Source voltage The explanation: The GOAL of an INVERTING CIRCUIT is to express output voltage VO as a function of source voltage vs.

Discussion

12.	Given Op-amp is ideal. Calculate vo if va=1v and vb=0v.(a) -4v(b) -2.5v(c) 4v(d) 2.5vThe question was asked during an online exam.The query is from Operational Amplifier Terminals,Terminal Voltages and Currents topic in portion The Operational Amplifier of Electric Circuits
Answer» The correct option is (b) -2.5v To explain I WOULD SAY: In the given circuit, a NEGATIVE feedback exists between Op-amp’s output and its inverting input (voltage here is 0, as vp =vb=0 and vn=vp). Node-voltage equation is i50=i125=i0. i50= (va-vn)/50 =1/50 mA. I125= (v0-vn)/125 = v0/125 mA. 1/50 + v0/125 = 0. v0 is -2.5volts.

Discussion

13.	The opamp in the Inverting circuit is in __________(a) Linear region(b) Saturation(c) Cut-off region(d) Non-linear regionThis question was posed to me during a job interview.This interesting question is from The Inverting and Non-Inverting Amplifier Circuit in chapter The Operational Amplifier of Electric Circuits
Answer» RIGHT choice is (a) Linear REGION To EXPLAIN: We ASSUME that the opamp is in linear region.

Discussion

14.	Calculate the gain for the Op-amp given.(a) 0.719(b) 2.572(c) 1.390(d) 1.237I had been asked this question during an interview.Origin of the question is Operational Amplifier Terminals,Terminal Voltages and Currents topic in division The Operational Amplifier of Electric Circuits
Answer» The CORRECT OPTION is (C) 1.390 Explanation: GAIN= Vout/Vin= -R2/R1 = -5.9810^-3/4.310^-3.

Discussion

15.	Find the gain for the following circuit.(a) -2(b) 2(c) -1(d) 1I had been asked this question in an interview for internship.The question is from Operational Amplifier Terminals,Terminal Voltages and Currents in division The Operational Amplifier of Electric Circuits
Answer» Correct option is (a) -2 To explain: In this circuit, the only NODE is at the negative TERMINAL of the Op-amp (SAY Vn) and by ideal rules of Op-amp, Vn= VP =0(in this circuit).Gain= Vout/Vin= -R2/R1.

Discussion

16.	The negative feedback causes the input voltage difference to ____________(a) 1(b) Increase(c) Decrease(d) 0I got this question in exam.My enquiry is from Operational Amplifier Terminals,Terminal Voltages and Currents in chapter The Operational Amplifier of Electric Circuits
Answer» Correct answer is (c) Decrease To EXPLAIN I would SAY: Negative feedback means a SIGNAL is fed back from OUTPUT terminals to the non-inverting input terminals and this results in a decrease in input voltage difference.

Discussion

17.	If the output voltage is not a linear function of input voltage then ____________(a) Op-amp acts a linear device(b) Op-amp acts as a non-linear device(c) Op-amp acts a polar device(d) Op-amp acts as an inverterThe question was asked during a job interview.This is a very interesting question from Operational Amplifier Terminals,Terminal Voltages and Currents topic in chapter The Operational Amplifier of Electric Circuits
Answer» Right answer is (b) Op-amp ACTS as a non-LINEAR device Best explanation: If output VOLTAGE is not a linear function of input voltage then Op-amp acts as a non-linear device.

Discussion

18.	When the input voltage difference is small in magnitude, the Op-amp behaves as ____________(a) Non-linear device(b) Linear device(c) Complex device(d) Bipolar deviceI had been asked this question during an online exam.Enquiry is from Operational Amplifier Terminals,Terminal Voltages and Currents in division The Operational Amplifier of Electric Circuits
Answer» The CORRECT CHOICE is (b) Linear device To EXPLAIN: When │vp-vn│is small then Op-amp acts as a linear device as the output voltage is a linear function of input VOLTAGES.

Discussion

19.	The number of terminals in an Op-amp ______________(a) 6(b) 2(c) 5(d) 3I got this question during an interview for a job.This intriguing question originated from Operational Amplifier Terminals,Terminal Voltages and Currents in portion The Operational Amplifier of Electric Circuits
Answer» RIGHT choice is (c) 5 For explanation: Inverting input, the Non-inverting input, Output, POSITIVE POWER SUPPLY, NEGATIVE power supply.

Discussion

20.	The Op-amp is a type of ___________(a) Differential amplifier(b) Integrated amplifier(c) Isolation amplifier(d) Feedback amplifierI got this question in a national level competition.This key question is from Operational Amplifier Terminals,Terminal Voltages and Currents in portion The Operational Amplifier of Electric Circuits
Answer» The correct choice is (a) DIFFERENTIAL amplifier To ELABORATE: The Op-amp is a TYPE of differential amplifier.

Discussion

21.	In the circuit of Op-amp given V- stands for _________(a) Non-inverting input(b) Non-inverting output(c) Inverting input(d) Inverting outputI had been asked this question in an interview for internship.I would like to ask this question from Operational Amplifier Terminals,Terminal Voltages and Currents topic in chapter The Operational Amplifier of Electric Circuits
Answer» The CORRECT OPTION is (c) Inverting input For EXPLANATION I WOULD SAY: V+: Non-inverting input and V- : Inverting input.

Discussion

22.	Op-amp was introduced by __________(a) Fairchild(b) Maxwell(c) Rutherford(d) SahaniThis question was posed to me in final exam.Question is from Operational Amplifier Terminals,Terminal Voltages and Currents topic in division The Operational Amplifier of Electric Circuits
Answer» Right CHOICE is (a) FAIRCHILD Easy explanation: Op-amp was INTRODUCED by Fairchild SEMICONDUCTOR in 1968.

Discussion

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If VCC = 12V and vs=1mV, then Rf/Rsis _____________(a) >12000(b)

Given Op-amp is ideal. Calculate vo if va=1v and vb=0v.(a) -4v(b) -2.5v(c) 4v(d) 2.5vThe question was asked during an online exam.The query is from Operational Amplifier Terminals,Terminal Voltages and Currents topic in portion The Operational Amplifier of Electric Circuits

Calculate the gain for the Op-amp given.(a) 0.719(b) 2.572(c) 1.390(d) 1.237I had been asked this question during an interview.Origin of the question is Operational Amplifier Terminals,Terminal Voltages and Currents topic in division The Operational Amplifier of Electric Circuits

Find the gain for the following circuit.(a) -2(b) 2(c) -1(d) 1I had been asked this question in an interview for internship.The question is from Operational Amplifier Terminals,Terminal Voltages and Currents in division The Operational Amplifier of Electric Circuits

The negative feedback causes the input voltage difference to ____________(a) 1(b) Increase(c) Decrease(d) 0I got this question in exam.My enquiry is from Operational Amplifier Terminals,Terminal Voltages and Currents in chapter The Operational Amplifier of Electric Circuits

The number of terminals in an Op-amp ______________(a) 6(b) 2(c) 5(d) 3I got this question during an interview for a job.This intriguing question originated from Operational Amplifier Terminals,Terminal Voltages and Currents in portion The Operational Amplifier of Electric Circuits

Op-amp was introduced by __________(a) Fairchild(b) Maxwell(c) Rutherford(d) SahaniThis question was posed to me in final exam.Question is from Operational Amplifier Terminals,Terminal Voltages and Currents topic in division The Operational Amplifier of Electric Circuits