McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
| 1. |
Which of the following condition is true for cut-off mode? |
| A. | the collector current is zero |
| B. | the collector current is proportional to the base current |
| C. | the base current is non zero |
| D. | all of the mentioned |
| Answer» A. the collector current is zero | |
| Explanation: the base current as well as the collector current are zero in cut-off mode. | |
| 2. |
Which of the following is true for the cut- off region in an npn transistor? |
| A. | potential difference between the emitter and the base is smaller than 0.5v |
| B. | potential difference between the emitter and the base is smaller than 0.4v |
| C. | the collector current increases with the increase in the base current |
| D. | the collector current is always zero and the base current is always non zero |
| Answer» B. potential difference between the emitter and the base is smaller than 0.4v | |
| Explanation: both collector and emitter current are zero in cut-off region. | |
| 3. |
Which of the following is true for a typical active region of an npn transistor? |
| A. | the potential difference between the emitter and the collector is less than 0.5 v |
| B. | the potential difference between the emitter and the collector is less than 0.4 v |
| C. | the potential difference between the emitter and the collector is less than 0.3 v |
| D. | the potential difference between the emitter and the collector is less than 0.2 v |
| Answer» C. the potential difference between the emitter and the collector is less than 0.3 v | |
| Explanation: most commonly used transistors have vce less than 0.4 v for the active region. | |
| 4. |
Which of the following is true for the active region of an npn transistor? |
| A. | the collector current is directly proportional to the base current |
| B. | the potential difference between the emitter and the collector is less than 0.4 v |
| C. | all of the mentioned |
| D. | none of the mentioned |
| Answer» C. all of the mentioned | |
| Explanation: the base current and the collector current are directly proportional to each other and the potential difference between the collector and the base is always less than 0.4 v. | |
| 5. |
Which of the following is true for a npn transistor in the saturation region? |
| A. | the potential difference between the collector and the base is approximately 0.2v |
| B. | the potential difference between the collector and the base is approximately 0.3v |
| C. | the potential difference between the collector and the base is approximately 0.4v |
| D. | the potential difference between the collector and the base is approximately 0.5v |
| Answer» D. the potential difference between the collector and the base is approximately 0.5v | |
| Explanation: the commonly used npn transistors have a potential difference of around 0.5v between he collector and the base. | |
| 6. |
The potential difference between the base and the collector Vcb in a pnp transistor in saturation region is |
| A. | -0.2 v |
| B. | -0.5v |
| C. | 0.2 v |
| D. | 0.5 v |
| Answer» B. -0.5v | |
| Explanation: the value of vcb is -0.5v for a pnp transistor and 0.5v for an npn transistor. | |
| 7. |
For a pnp transistor in the active region the value of Vce (potential difference between the collector and the base) is |
| A. | less than 0.3v |
| B. | less than 3v |
| C. | greater than 0.3v |
| D. | greater than 3v |
| Answer» A. less than 0.3v | |
| Explanation: for a pnp transistor vce is less | |
| 8. |
Which of the following is true for a pnp transistor in active region? |
| A. | cb junction is reversed bias and the eb junction is forward bias |
| B. | cb junction is forward bias and the eb junction is forward bias |
| C. | cb junction is forward bias and the eb junction is reverse bias |
| D. | cb junction is reversed bias and the eb junction is reverse bias |
| Answer» A. cb junction is reversed bias and the eb junction is forward bias | |
| Explanation: whether the transistor in npn or pnp, for it be in active region the eb junction must be reversed bias the cb junction must be forward bias. | |
| 9. |
Which of the following is true for a pnp transistor in saturation region? |
| A. | cb junction is reversed bias and the eb junction is forward bias |
| B. | cb junction is forward bias and the eb junction is forward bias |
| C. | cb junction is forward bias and the eb junction is reverse bias |
| D. | cb junction is reversed bias and the eb junction is reverse bias |
| Answer» B. cb junction is forward bias and the eb junction is forward bias | |
| Explanation: whether the transistor in npn or pnp, for it be in saturation region the eb junction must be forward bias the cb junction must be forward bias. | |
| 10. |
For the circuit shown, find the quiescent point. |
| A. | none of the below |
| B. | (4v, 10ma) |
| C. | (10v, 3ma) |
| D. | (3ma, 10v) |
| Answer» C. (10v, 3ma) | |
| Explanation: we know, ie=vee/re=30/10kΩ=3ma ic=α ie =ie =3ma | |
| 11. |
What is the DC characteristic used to prove that the transistor is indeed biased in saturation mode? |
| A. | ic = βib |
| B. | ic > βib |
| C. | ic >> βib |
| D. | ic < βib |
| Answer» D. ic < βib | |
| Explanation: when in a transistor is driven into saturation, we use vce(sat) as another linear parameter. in, addition when a transistor is biased in saturation mode, we have ic < βib. this characteristic used to prove that the transistor is indeed biased in saturation mode. | |
| 12. |
The feature of an approximate model of a transistor is |
| A. | it helps in quicker analysis |
| B. | it provides individual analysis for different configurations |
| C. | it helps in dc analysis |
| D. | ac analysis is not possible |
| Answer» A. it helps in quicker analysis | |
| Explanation: the small signal model helps in quicker ac analysis of a transistor. the approximate model is applicable for all the configurations. the dc analysis is not obtained by using a small signal model of transistor. | |
| 13. |
005mmhos, hre=0. Find the output impedance if the lad resistance is 5kΩ. |
| A. | 5kΩ |
| B. | 4kΩ |
| C. | 20kΩ |
| D. | 15kΩ |
| Answer» B. 4kΩ | |
| Explanation: ro=i/hoe=1/0.005m | |
| 14. |
A transistor has hie =2kΩ, hoe=25µmhos and hfe=60 with an unbypassed emitter resistor Re=1kΩ. What will be the input resistance and output resistance? |
| A. | 90kΩ and 50kΩ respectively |
| B. | 33kΩ and 45kΩ respectively |
| C. | 6kΩ and 40kΩ respectively |
| D. | 63kΩ and 40kΩ respectively |
| Answer» D. 63kΩ and 40kΩ respectively | |
| Explanation: as the emitter is unbypassed, the input resistance ri=hie+(1+hfe)re | |
| 15. |
A transistor has hie =1KΩ and hfe=60 with an bypassed emitter resistor Re=1kΩ. What will be the input resistance and output resistance? |
| A. | 90kΩ and 50kΩ respectively |
| B. | 33kΩ and 45kΩ respectively |
| C. | 6kΩ and 40kΩ respectively |
| D. | 63kΩ and 40kΩ respectively |
| Answer» D. 63kΩ and 40kΩ respectively | |
| Explanation: as the emitter is bypassed, the input resistance ri=hie | |
| 16. |
In the given circuit, find the equivalent resistance between A and B nodes. |
| A. | 100kΩ |
| B. | 50kΩ |
| C. | 40kΩ |
| D. | 60kΩ |
| Answer» B. 50kΩ | |
| Explanation: rab=ro | |
| 17. |
Which of the following acts as a buffer? |
| A. | cc amplifier |
| B. | ce amplifier |
| C. | cb amplifier |
| D. | cascaded amplifier |
| Answer» A. cc amplifier | |
| Explanation: the voltage gain of a common collector amplifier is unity. it is then used as a buffer. the cc amplifier is also called as an emitter follower. though there is no amplification done, the output will be stabilised. | |
| 18. |
Which of the following is true? |
| A. | cc amplifier has a large current gain |
| B. | ce amplifier has a large current gain |
| C. | cb amplifier has low voltage gain |
| D. | cc amplifier has low current gain |
| Answer» B. ce amplifier has a large current gain | |
| Explanation: the ce amplifier has high current and voltage gains. the cc amplifier has unity voltage gain which cannot be regarded as high. the common base amplifier has a unity current gain and high voltage gain. | |
| 19. |
In CB configuration, the value of α=0.98A. A voltage drop of 4.9V is obtained across the resistor of 5KΩ when connected in collector circuit. Find the base current. |
| A. | 0.01ma |
| B. | 0.07ma |
| C. | 0.02ma |
| D. | 0.05ma |
| Answer» C. 0.02ma | |
| Explanation: here, ic=4.9/5k=0.98ma α = ic/ie .so, | |
| 20. |
Which of the following is the correct relationship between base and emitter current of a BJT? |
| A. | ib = β ie |
| B. | ib = ie |
| C. | ib = (β + 1) ie |
| D. | ie = (β + 1) ib |
| Answer» D. ie = (β + 1) ib | |
| Explanation: for a bjt, the collector current | |
| 21. |
For best operation of a BJT, which region must the operating point be set at? |
| A. | active region |
| B. | cutoff region |
| C. | saturation region |
| D. | reverse active region |
| Answer» A. active region | |
| Explanation: operating point for a bjt must always be set in the active region to ensure proper functioning. setting up of q-point in any other region may lead to reduced functionality. | |
| 22. |
From the given circuit, using a silicon transistor, what is the value of IBQ? |
| A. | 47.08 ma |
| B. | 47.08 ua |
| C. | 50 ua |
| D. | 0 ma |
| Answer» B. 47.08 ua | |
| Explanation: consider the bjt to be in saturation. then ic=12-0.2/2.2k=5.36 ma and ib=12-0.8/240k=0.047 ma ibmin=icsat/β=5.09/50=0.1072ma which is | |
| 23. |
From the given circuit, using a silicon BJT, what is the value of VCEQ? |
| A. | 7 v |
| B. | 0.7 v |
| C. | 6.83 v |
| D. | 7.17 v |
| Answer» C. 6.83 v | |
| Explanation: consider the bjt to be in saturation. then ic=12-0.2/2.2k=5.36 ma and ib=12-0.8/240k=0.047 ma ibmin=icsat/β=5.09/50=0.1072ma which is | |
| 24. |
From the given circuit, using a silicon BJT, what is the value of VBC? |
| A. | 6.13 v |
| B. | -6.13 v |
| C. | 7 v |
| D. | -7 v |
| Answer» B. -6.13 v | |
| Explanation: consider the bjt to be in saturation. then ic=12-0.2/2.2k=5.36 ma and ib=12-0.8/240k=0.047 ma ibmin=icsat/β=5.09/50=0.1072ma which is | |
| 25. |
From the given circuit, using silicon BJT, what is the value of the saturation collector current? |
| A. | 5 ma |
| B. | 5.36 ma |
| C. | 5.45 ma |
| D. | 10.9 ma |
| Answer» B. 5.36 ma | |
| Explanation: to obtain an approximate answer, under saturation the bjt is on and hence acts like a short circuit. however, ideally a drop exists for the transistor which is a fixed value. for an exact answer, if the bjt is a silicon transistor, then drop vce = 0.2v and current is 12-0.2/2.2=5.36 ma. | |
| 26. |
In the given circuit, what is the value of IC if the BJT is made of Silicon? |
| A. | 2.01 ma |
| B. | 2.01 ua |
| C. | 10.05 ma |
| D. | 10.05 ua |
| Answer» A. 2.01 ma | |
| Explanation: consider the bjt to be in saturation. then ic=20-0.2/2k=9.9 ma and ib=20-0.8/430k=0.044 ma | |
| 27. |
In the given circuit, using a silicon BJT, what is the value of VCE? |
| A. | 20 v |
| B. | 15.52 v |
| C. | 14.98 v |
| D. | 13.97 v |
| Answer» B. 15.52 v | |
| Explanation: consider the bjt to be in saturation. then ic=20-0.2/2k=9.9 ma and ib=20-0.8/430k=0.044 ma | |
| 28. |
In the given circuit, what is the value of VE when using a silicon BJT? |
| A. | 2.01 v |
| B. | 0.28 v |
| C. | 0 v |
| D. | 2.28 v |
| Answer» D. 2.28 v | |
| Explanation: consider the bjt to be in saturation. then ic=20-0.2/2k=9.9 ma and ib=20-0.8/430k=0.044 ma | |
| 29. |
In the given circuit using a silicon BJT, what is the value of saturation collector current? |
| A. | 10 ma |
| B. | 8.77 ma |
| C. | 6.67 ma |
| D. | 5 ma |
| Answer» C. 6.67 ma | |
| Explanation: to obtain an approximate answer, under saturation the bjt is on and hence acts like a short circuit. however, ideally a drop exists for the transistor which is a fixed value. for an exact answer, if the bjt is a silicon transistor, then drop vce = 0.2v and current is 20-0.2/2.2=9.9 ma. | |
| 30. |
What is Stability factor? |
| A. | ratio of change in collector current to change in a current amplification factor |
| B. | ratio of change in collector current to change in base current |
| C. | current amplification factor |
| D. | ratio of base current to collector current |
| Answer» A. ratio of change in collector current to change in a current amplification factor | |
| Explanation: stability factor is defined as the rate at which collector current changes when base to emitter voltage changes, keeping base | |
| 31. |
The base current for a BJT remains constant at 5mA, the collector current changes from 0.2mA to 0.3 mA and beta was changed from 100 to 110, then calculate the value of S. |
| A. | 0.01m |
| B. | 1m |
| C. | 100m |
| D. | 25m |
| Answer» A. 0.01m | |
| Explanation: since the current in the above case, remains constant, therefore stability factor is 0.01 as it is defined as the ratio of change in collector current to change in beta. s=change in collector current/change in beta=0.1ma/10=0.01m. | |
| 32. |
For a n-p-n transistor, the collector current changed from 0.2mA to 0.22mA resulting a change of base emitter voltage from 0.8v to 0.8005V. What is the value of Stability factor? |
| A. | 0 |
| B. | 0.25 |
| C. | 0.04 |
| D. | 0.333 |
| Answer» C. 0.04 | |
| Explanation: change in vbe = 0.0005v change in collector current = 0.02ma | |
| 33. |
There are two transistors A and B having ‘S’ as 25 and 250 respectively, on comparing the value of S, we can say B is more stable than A. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: more the value of s, lesser the stability, since a has lesser s value the | |
| 34. |
For a fixed bias circuit having Ic = 0.3mA and In=0.0003mA, S is |
| A. | 100 |
| B. | 0 |
| C. | 11 |
| D. | 111 |
| Answer» C. 11 | |
| Explanation: for fixed bias s=1+beta beta=ic/ib=10 | |
| 35. |
For a fixed bias circuit having RC=2Kohm and VCC=60V, IB=0.25mA and S=101, find Vce. |
| A. | 12v |
| B. | 10v |
| C. | 5v |
| D. | 2.5v |
| Answer» B. 10v | |
| Explanation: s = 1 + beta, | |
| 36. |
For an ideal transistor having a fixed bias configuration, what will be the value of Beta? |
| A. | 0 |
| B. | 2 |
| C. | -1 |
| D. | 1 |
| Answer» C. -1 | |
| Explanation: s = 1 + beta s = 0 | |
| 37. |
The temperature changes do not affect the Stability. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: the temperature changes the value of beta which in turn changes the stability of the transition. the temperature changes affect the mobility of the charge carries which results in a change of the current parameters affecting stability. | |
| 38. |
Comparing fixed and collector to base bias which of the following statement is true? |
| A. | fixed bias is more stable |
| B. | collector to base bias is more stable |
| C. | both are the same in terms of stability |
| D. | depends on the design |
| Answer» B. collector to base bias is more stable | |
| Explanation: for fixed bias circuit, s = 1+beta, more the beta, lesser the stability for collector to base bias s = (1+beta)/(1+beta(rc/rc+rb)) | |
| 39. |
The compensation techniques are used to |
| A. | increase stability |
| B. | increase the voltage gain |
| C. | improve negative feedback |
| D. | decrease voltage gain |
| Answer» B. increase the voltage gain | |
| Explanation: usually, the negative feedback is used to produce a stable operating point. | |
| 40. |
Compensation techniques refer to the use of |
| A. | diodes |
| B. | capacitors |
| C. | resistors |
| D. | transformers |
| Answer» A. diodes | |
| Explanation: compensation techniques refer to the use of temperature sensitive devices such as thermistors, diodes, transistors, sensistors etc to compensate variation in currents. sometimes for excellent bias and thermal stabilization, both stabilization and compensation techniques are used. | |
| 41. |
In a silicon transistor, which of the following change significantly to the change in IC? |
| A. | vce |
| B. | ib |
| C. | vbe |
| D. | b) ie |
| Answer» C. vbe | |
| Explanation: for germanium transistor, changes in ico with temperature contribute more serious problem than for silicon transistor. on the other hand, in a silicon transistor, the changes of vbe with | |
| 42. |
What is the compensation element used for variation in VBE and ICO? |
| A. | diodes |
| B. | capacitors |
| C. | resistors |
| D. | transformers |
| Answer» A. diodes | |
| Explanation: a diode is used as the compensation element used variation in vbe and ico. the diode used is of the same material and type as that of transistor. hence, the voltage across the diode has same temperature coefficient as vbe of the transistor. | |
| 43. |
The expression for IC in the compensation for instability due to ICO variation |
| A. | βi+βio+βico |
| B. | βi+βio |
| C. | βio+βico |
| D. | βi+βico |
| Answer» A. βi+βio+βico | |
| Explanation: in this method, diode is used for the compensation in variation of ico. the diode used is of the same material and type as that of transistor. hence, the reverse saturation current io of the diode will increase with temperature at the same rate as the transistor collector saturation current ico. | |
| 44. |
Which of the following has a negative temperature coefficient of resistance? |
| A. | sensistor |
| B. | diode |
| C. | thermistor |
| D. | capacitor |
| Answer» C. thermistor | |
| Explanation: the thermistor has a negative temperature coefficient of resistance. it | |
| 45. |
Which of the following has a negative temperature coefficient of resistance? |
| A. | capacitor |
| B. | diode |
| C. | thermistor |
| D. | sensistor |
| Answer» D. sensistor | |
| Explanation: the sensistor has a positive temperature coefficient of resistance. it is a temperature sensitive resistor. it is a heavily doped semiconductor. when voltage is decreased, the net forward emitter voltage decreases. as a result the collector current decreases. | |
| 46. |
Increase in collector emitter voltage from 5V to 8V causes increase in collector current from 5mA to 5.3mA. Determine the dynamic output resistance. |
| A. | 20kΩ |
| B. | 10kΩ |
| C. | 50kΩ |
| D. | 60kΩ |
| Answer» B. 10kΩ | |
| Explanation: ro=∆vce/∆ic | |
| 47. |
The output resistance of CB transistor is given by |
| A. | ∆vcb/∆ic |
| B. | ∆vbe/∆ib |
| C. | ∆vbe/∆ic |
| D. | ∆veb/∆ie |
| Answer» A. ∆vcb/∆ic | |
| Explanation: the ratio of change in collector base voltage (∆vcb) to resulting change in collector current (∆ic) at constant emitter current (ie) is defined as output resistance. | |
| 48. |
The negative sign in the formula of amplification factor indicates |
| A. | that ie flows into transistor while ic flows out it |
| B. | that ic flows into transistor while ie flows out it |
| C. | that ib flows into transistor while ic flows out it |
| D. | that ic flows into transistor while ib flows out it |
| Answer» A. that ie flows into transistor while ic flows out it | |
| Explanation: when no signal is applied, the ratio of collector current to emitter current is called dc alpha, αdc of a transistor. αdc=- ic/ie. it is the measure of the quality of a transistor. higher is the value of α, better is the transistor in the sense that collector current approaches the emitter current. | |
| 49. |
In the given situation for n-channel JFET, we get drain-to-source current is 5mA. What is the current when VGS = – 6V? |
| A. | 5 ma |
| B. | 0.5a |
| C. | 0.125 a |
| D. | 0.5a |
| Answer» C. 0.125 a | |
| Explanation: ids = idss(1-vgs/vp)2 when vgs = 0, idss = ids = 5ma when vgs = -6v, ids = 5ma(1 + 4)2 ids = 5 x 25 = 125 ma. | |
| 50. |
7 BIASING BJT SWITCHING CIRCUITSJFET - DC LOAD LINE AND BIAS POINT, VARIOUS BIASING METHODS OF JFET - JFET BIAS CIRCUIT DESIGN |
| A. | rd < 6kΩ |
| B. | rd > 6kΩ |
| C. | rd > 4kΩ |
| D. | rd < 4kΩ |
| Answer» A. rd < 6kΩ | |
| Explanation: in given circuit, vgs = -5v vds = vdd – idsrd | |
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