SOLID STATE ELECTRONICS & DIGITAL ELECTRONICS

CET QUESTION PAPER

GAYATHRI. M .S. Lecturer in Physics

C.E.T QUESTION PAPER

SOLID STATE ELECTRONICS & DIGITAL ELECTRONICS

Note Answer all the questions.

1. In a semiconductor conduction band and valence band are

1) Separated by a relatively small energy gap

2) Overlapped

3) Separated by a small energy gap

4) separated by a large energy gap

2. Electric conduction takes place in a semiconductor due to

1) Holes only

2) Electrons only

3) Both holes and electrons

4) neither electrons nor holes

3. An n-type semiconductor is obtained by doping

1) Pure semiconductor with 5th group element

2) Pure semiconductor with 3rd group element

3) 3rd group element with pure semiconductor

4) 5th group element with pure semiconductor

4. Two identical capacitors A & B are charged to same potential ‘V’ and are

connected in two circuits at t=0 as shown in the figure. The charges on the

capacitor at time t=CR are respectively

1) VC, VC

2) VC, VC/e

3) VC/e, VC

4) VC/e, VC/e

CET QUESTION PAPER


5. When a potential difference is applied across, the current passing through

1) An insulator at zero Kelvin is not zero

2) A semiconductor at zero Kelvin is zero

3) A metal at zero Kelvin is finite

4) A p-n junction diode at 300 K is finite if it is reverse biased

6. The value of V0 and I if the silicon diode and the germanium diode conducts

at 0.7 V and 0.3 V respectively is

1) 5.7V, 3mA

2) 3mA , 5.7V

3) 4.99V, 2.63mA

4) 5.29V, 2.78Ma

7. The electrical conductivity of a semiconductor increases when a radiation of

wavelength shorter than 2475 nm is incident on it. The band gap for the

semiconductor in eV is

1) 0.7

2) 0.9

3) 0.5

4) 1.1

CET QUESTION PAPER


8. The circuit shown contains two diodes with a forward resistance of 40Ω and

infinite reverse resistance. If the battery voltage is 3V the current through50Ω

resistor is

1) Zero

2) 0.02A

3) 0.027A

4) 0.05 1A

9. Assertion: The resistivity of a semiconductor increases with temperature

Reason: The atoms of a semiconductor vibrate with larger amplitude at higher

temperature thereby increasing its resistivity.

1) Both assertion and reason are true and the reason is correct explanation

of the assertion

2) Both assertion and reason are true and the reason is correct explanation

of assertion

3) Assertion is true but reason is false

4) Both assertion and reason are false

10. In positive logic, the logic state 1 corresponds to

1) positive voltage

2) zero voltage

3) low voltage

4) higher voltage level

CET QUESTION PAPER


11. The output states in of X & Y in the figure is

1) 1,0

2) 0,1

3) 0,0

4) 1,1

12. In the following circuit the outpu waveform Vo across RL due to lower

diode D2 is

1) B,D

2) A,B

3) A,C

4) B,C

13. The following figure represents

1) 1 as npn, 2 as pnp transistor

2) 1 as pnp, 2 as npn transistor

3) both 1 & 2 are pnp transistor

4) both 1 & 2 are npn transistor

CET QUESTION PAPER


14. The following diagram performs the logic function of

1) NAND

2) AND

3) OR

4) XOR

15. Which of the following statement is not true

1) A p-n junction diode acts as a semi-conductor diode

2) The majority charge carriers in n-type semi-conductors are holes

3) Doping pure silicon with trivalent impurity gives p-type semi-conductor

4) The resistance of intrinsic semi-conductor decreases with increase of

temperature

16. The dominant mechanism for motion of charge carriers in forward

&reverse biased silicon p-n junction are

1) Drift in forward bias, Diffusion in reverse bias

2) Drift in reverse bias, Diffusion in forward bias

3) Diffusion in both forward & reverse bias

4) Drift in both forward & reverse bias

17. When a p-n junction diode is reverse biased the flow of current across

the junction is mainly due to

1) Diffusion of charges

2) Depends upon the nature of material

3) Drift of charges

4) Both drift & diffusion of charges

18.When n-p-n transistor is used as an amplifier

1) electrons move from base to collector

2) electrons move from collector to base

3) holes move from emitter to base

4) holes move from base to emitter

CET QUESTION PAPER


19. A semiconducting device is connected in a series circuit with a battery

and a resistance. A current is found to pass through the circuit. If the polarity

of the battery is reversed the current drops to almost zero. The device may be

1) an intrinsic semiconductor

2) a p-type semiconductor

3) an n-type semiconductor

4) a p-n junction

20. Doping materials are called impurities because they

1) Alter the crystal structure 2) Change the number of charge carriers 3) Change the chemical properties 4) Make semiconductors impure

21. In a conductor conduction band and valence band are

1) separated by a relatively small energy gap 2) overlapped 3) separated by a small energy gap 4) separated by a large energy gap

22. In an insulator conduction band and valence band are

1) Separated by a relatively small energy gap 2) Overlapped 3) Separated by a small energy gap 4) Separated by a large energy gap

23. If np and ne are number of holes and electrons respectively, then in an

intrinsic semiconductor

1) 𝑛𝑝 > 𝑛𝑒

2) 𝑛𝑝 = 𝑛𝑒

3) 𝑛𝑝 < 𝑛𝑒

4) 𝑛𝑝 ≠ 𝑛𝑒

CET QUESTION PAPER


24. If np and ne are number of holes and electrons respectively, then in a p-

type semiconductor

1) 𝑛𝑝 > 𝑛𝑒

2) 𝑛𝑝 = 𝑛𝑒

3) 𝑛𝑝 < 𝑛𝑒

4) 𝑛𝑝 ≠ 𝑛𝑒

25. A p-type semiconductor is

1) Positively charged

2) Negatively charged

3) uncharged

4) Uncharged at 0K but positively charged at higher temperature

26. A pure semiconductor is doped with some impurity. Its conductivity

1) Increases

2) Decreasesr

3) remains the same

4) becomes zero

27. In a p-type semiconductor

1) Majority charge carriers are holes and minority charge carriers are

electrons

2) Majority charge carriers are only electrons

3) Majority charge carriers are only holes

4) Majority charge carriers are electrons and minority charge carriers are

holes

28. In an n-type semiconductor

1) Majority charge carriers are holes and minority charge carriers are

electrons

2) Majority charge carriers are only electrons

3) Majority charge carriers are only holes

4) Majority charge carriers are electrons and minority charge carriers are

holes

CET QUESTION PAPER


29. The drift current in a p-n junction is from

1) n-side to p-side if the junction is unbiased

2) P-side to n-side if the junction is unbiased

3) n-side to p-side if the junction is forward biased

4) n-side to p-side if the junction is reverse biased

30. If the two ends of a p-n junction are joined by a wire

1) There is no steady current in the wire

2) There is steady current in the wire

3) There is steady current from p-side to n-side

4) May or may not be current depends on the resistance of the wire

31. The diffusion current in a p-n junction is from

1) n-side to p-side if the junction is unbiased

2) p-side to n-side if the junction is unbiased

3) n-side to p-side if the junction is forward biased

4) n-side to p-side if the junction is reverse biased

32. A rectifier is a device used to

1) Convert a.c.to d.c

2) Convert d.c to a.c

3) Amplify a.c.signal

4) Step-up or step-down ac

33. Which of the following device is used to rectify a.c?

1) Diode

2) Transistor

3) Transformer

4) Capacitor

CET QUESTION PAPER


34. The main distinction between conductors, semiconductors and insulators is

because of

1) Width of the forbidden band

2) Binding energy of electrons

3) Temperature co-efficient of resistance

4) Work function

35. The resistance of pure semiconductor at absolute zero is

1) Zero

2) finite but not zero

3) infinite

4) very high but not infinite

36. The electric current through a semiconductor is due to the drifting of

1) Holes

2) electrons

3) both electrons & holes

4) neither electrons nor holes

37. At absolute zero germanium behaves as

1) Conductor

2) semi conductor

3) super conductor

4) insulator

38. In a semi conductor the majority charge carriers are

1) Holes in p-type and electrons in n-type semiconductor

2) Holes in n-type and electrons in p-type semi conductor

3) Holes in both p-type and n-type semiconductor

4) Electrons in both p-type and n-type semiconductor

CET QUESTION PAPER


39. A piece of aluminium and germanium are cooled from room temperature

to 50K. Their resistivity

1) Decrease in both

2) Increase in both

3) Decreases in aluminium and increases in germanium

4) Increases in aluminium and decreases in germanium

40. The holes exist in

1) Intrinsic semi conductor

2) Extrinsic semiconductor

3) Donor impurities

4) Acceptor impurities

41. The resistivity of a semiconductor depends on

1) Area of cross section

2) Length of the semiconductor

3) Nature of atoms

4) Size of the semiconductor

42. The electrical conductivity of a p-type semi conductor is determined by

1) Holes

2) Impurity atoms alone

3) Electrons in the valence band

4) Free electrons in the conduction band

43. The resistivity of a pure semiconductor at absolute zero is

1) Zero

2) Infinity

3) Same as that of the conductors at room temperature

4) Same as that of the insulators at room temperature

CET QUESTION PAPER


44. In a transistor the emitter-base junction is

1) forward biased

2) reverse biased

3) unbiased

4) biasing is not necessary

45. In a transistor the collector-base junction is

1) forward biased

2) reverse biased

3) unbiased

4) biasing is not necessary

46. In a p-n-p transistor p-type crystal acts as

1) only emitter

2) only collector

3) only base

4) both emitter as wel as collector

47. In an n-p-n transistor p-type crystal acts as

1) only emitter

2) only collector

3) only base

4) both emitter as wel as collector

48. When two semiconductors of p-type and n-type are brought into

contact, they form a p-n junction which acts like a

1) Rectifier

2) Conductor

3) Amplifier

4) Oscillator

CET QUESTION PAPER


49. The doping level is maximum in the emitter region of a transistor

because it

1) is a suppliers of charge carriers

2) dissipates maximum power

3) receives the input

4) to have low resistance

50. When the diode is forward biased the depletion region acts as

1) Conductor

2) Insulator

3) Semiconductor

4) super conductor

51. Which of the following gives output `1 in AND gate

1) A=0, B=0

2) A=0, B=1

3) A=1, B=0

4) A=1, B=1

52. Digital circuits can be made by repetitive use of

1) OR gates

2) AND gates

3) NOT gates

4) NAND gates

53. NAND and NOR gates are called universal gates because they

1) are available everywhere

2) are widely used in integrated circuits

3) can be easily manufactured

4) can be combined to produce OR, AND & NOT gates

CET QUESTION PAPER


54. NOR gate is a series combination of

1) NOT gate followed by OR gate

2) OR gate followed by NOT gate

3) OR gate followed by AND gate

4) AND gate followed by OR gate

55. In a transistor the concentration of impurity is

1) least in the emitter region

2) least in the base region

3) maximum in the collector region

4) least in the collector region

56. For a transistor collector current is 25mA, base current is 1mA the value of alpha is

1) 25/26 2) 26/25 3) 24/25 4) 25/24

57. The semiconductor material having high negative temperature co-efficient of resistivity is

1) thermistor 2) insulator 3) conductor 4) transistor

58. Fermi energy is the maximum energy possessed by any electron at

1) 273K 2) 2730C 3) 0K 4) 300K

59. Donor type semiconductor is formed by adding impurity of valency

1) 3 2) 5 3) 4 4) 6

CET QUESTION PAPER


60. The three inputs of a full adder are 0,1 & 1. Then the carry and the sum will be

1) 0,1 2) 1,0 3) 0,0 4) 1,1

CET QUESTION PAPER


ANSWERS

1 1 16 2 31 2 46 4 2 3 17 1 32 1 47 3 3 1 18 1 33 1 48 1

4 3 19 4 34 1 49 1 5 2 20 1 35 3 50 1 6 1 21 2 36 3 51 4 7 3 22 4 37 4 52 4

8 2 23 2 38 1 53 4 9 4 24 1 39 3 54 2

10 4 25 3 40 2 55 2

11 2 26 1 41 3 56 1 12 1 27 1 42 1 57 1 13 2 28 4 43 2 58 3 14 2 29 1 44 1 59 2

15 2 30 1 45 2 60 2

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SOLID STATE ELECTRONICS & DIGITAL ELECTRONICS