33 Essential Interview Questions On Transistor(BJT, FET & MOSFET)

Most Frequently asked interview questions on transistor in the topic such as BJT, FET and MOSFET.

1.   BJT is

1. a voltage control device
2. a current controlled device
3. a temperature controlled device
4. none of these

Answer – (2)

2.   In NPN BJT electrons are energized in

1. forward biased junction
2. reverse biased junction
3. bulk region
4. both the junctions

Answer – (4)

3.   When a transistor operating at the central of the load line is declining, the current gain will change the Q-point

1. down
2. up
3. nowhere
4. of the load line

Answer – (3)

4.    The output voltage of a Common Emitter amplifier is

1. amplify
2. reverse
3. 180° out of the phase with the input
4. all of these

Answer – (1)

5.   The level of doping of emitter section of a transistor has to be

1. More than the collector and base.
2. Smaller than the collector and base.
3. lesser than the base region but greater than the collector region
4. More than base region only

Answer – (3)

6.   A BJT used in Common Emitter configured offers

1. low input & high output impedance
2. high input & low output impedance
3. low input & output impedances
4. high input & output impedances

Answer – (2)

7.   A bipolar junction transistor when used as a switch, operates in

1. cut-off and active region
2. active and saturation region
3. cut-off and saturation region
4. all of these

Answer – (3)

8.   If for CE model h_ie  = 1k.ohm, h_fe = 50 then for common collector model h_ie . h_fe will be

1. 1 k.ohm,50
2. 1k.ohm,51
3. 1/51 k.ohm,50
4. 1/51 k.ohm, -51

Answer -(2)

9.   The leakage current I_CBO flows through

1. base and emitter terminals
2. emitter and collector terminals
3. base and collector terminals
4. emitter,base and collector terminals

Answer – (3)

10. To turning OFF an SCR, it is essential to decrease current to be less than

1. trigger current
2. holding current
3. break over current
4. none of these

Answer – (1)

11. In a BJT, the base region should be very thin to minimalize the

1. drift current
2. diffusion current
3. recombination current
4. tunneling current

Answer – (3)

12.  A transistor configuration with the lowermost current gain is

1. common base
2. common emitter
3. common collector
4. emitter follower

Answer – (4)

13.  When a transistor is acting as a switch operate in

1. cut-off region
2. saturation region
3. active region
4. both a & b

Answer – (4)

14.  The Transistor is connected in Common Base configuration has

1. high input & low output resistance
2. low input & high output resistance
3. low input & low output resistance
4. high input & high output resistance

Answer – (1)

15.  An N-channel MOSFET, the source and drain region has to be doped with

1. n-type material
2. p-type material
3. source with p-type and drain with n-type material
4. none of these

Answer – (2)

16. JFET normally works

1. In the cut-off mode
2. In the saturation mode
3. In the Ohmic mode
4. In the break down mode

Answer – (3)

17. In a p-type MOSFET in accumulation region, the band bends

1. downwards
2. sideways
3. upwards
4. none of these

Answer – (3)

18.  When the drain saturation current is >= I_dss a JFET operate as

1. The bipolar transistor
2. The current source
3. Simple resistor
4. A battery

Answer – (3)

19. Strong inversion occurred in N-MOSFET for condition

1. Φ _s = Φ _F
2. Φ _s  = 2Φ _F
3. Φ _s  = 0
4. Φ _s < Φ _F

Where, Φ _s   and Φ _F   are surface and Fermi potential respectively

Answer – (2)

20. A D-MOSFET typically operate in

1. The depletion mode only.
2. The enhancement mode only.
3. The both depletion & enhancement mode.
4. The small impedance mode.

Answer – (3)

21. Ion implantation is done

1. at lower temperature than diffusion mode
2. at higher temperature than diffusion mode
3. at most same temperature as diffusion mode
4. none of these

Answer – (1)

22. The Flat band condition for an MOS capacitor is

1. Φ _s  = 0
2. Φ _s  > 0
3. Φ _s  < 0
4. Φ _s  = Φ _F

Answer – (1)

23. Inversion layer in an MOS circuit is made by

1. doping
2. impact ionization
3. tunneling
4. electric field

Answer – (4)

24. Compared to Field Effect Phototransistor, Bipolar Phototransistors are

1. more sensitive and faster
2. more sensitive and slower
3. less sensitive and slower
4. less sensitive and faster

Answer – (3)

25. Consider the following statements

The threshold voltage of a MOSFET can be increased by

• I. using thinner Gate Oxide
• II. reducing the substrate concentration
• III. increasing the substrate concentration of these

1. III alone is correct
2. I & II are correct
3. I & III are correct
4. II alone is correct

Answer – (2)

26. The function of the SiO₂ layer in MOSFET is to provide

1. The high input impedance
2. The high output impedance
3. flow of current carries within channel
4. both a & b

Answer – (3)

27. Above pinch off voltage in a JFET the drain current

1. decreases
2. increases sharply
3. remains constant
4. both a & b

Answer – (3)

28. If V is the voltage applied to the metal with respect to p-type semiconductor in a MOS capacitor then V<0 corresponds to

1. accumulation
2. depletion
3. inversion
4. strong inversion

Answer – (1)

29. Flat-Band voltage of n-channel enhancement type MOSFET is

1. positive
2. negative
3. positive or negative
4. zero

Answer – (1)

30. Which one of the following is not a voltage controlled circuit?

1. MOSFET
2. IGBT
3. BJT
4. JFET

Answer – (3)

31. Pinch off voltage of FET depends on

1. channel width
2. doping concentration of channel
3. applied voltage
4. both of a & b

Answer – (4)

32. For design of a high speed electronic system the preferred one should be

1. Si n-MOS
2. Si p-MOS
3. GaAs n-MOS
4. GaAs p-MOS

Answer – (3)

33. What is one significant thing transistors perform?

1. Amplify weak signals
2. Rectify line voltage
3. Regulate voltage
4. Emit light

Answer – (1)

34. The base of an NPN transistor is thin and

1. Heavily doped
2. Lightly doped
3. Metallic
4. Doped by a pentavalent material

Answer – (2)

35. Maximum no electrons in the base region of an NPN transistor will not recombine for reason being

1. Have a long lifetime
2. Have a negative charge
3. Must flow a long way through the base
4. Flow out of the base

Answer – (1)