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Worksheet on Semiconductors

Q1 On increasing the temperature the specific resistance of a semiconductor :-


a) increase

b) decreases

c) does not change

d) first decreases and then increases



Q2 Electric conduction in a semiconductor takes place due to :-


a) electrons only

b) holes only

c) both electrons and holes

d) neither electrons nor holes



Q3 A p-type semiconductor is :-


a) Positively charged

b) Negatively charged

c) Uncharged

d) Uncharged at OK but charged at higher temperatures



Q4 Which statement is correct for p – type semiconductor.


a) the number of electrons in conduction band is more than the number of holes in valence band at room temperature

b) the number of holes in valence band is more than the number of electrons in conduction band at room temperature

c) there are no holes and electrons at room temperature

d) number of holes and electrons is equal in valence and conduction band



Q5 When an impurity is doped into an intrinsic semiconductor, the conductivity of the semiconductor :


a) increases

b) decreases

c) remains the same

d) become zero



Q6 When we convert pure semiconductor into N type the number of hole :-


a) Increases

b) Decreases

c) Remains constant

d) None



Q7 A semiconductor is damaged by a strong current, because :-


a) lack of free electron

b) decrease in electrons

c) excess of electrons

d) none of these



Q8 In an intrinsic semiconductor, number of electrons and holes at room temperature are :-


a) equal

b) zero

c) unequal

d) infinity



Q9 In semiconductor, at room temperature :-


a) valence band are partially empty and conduction band are partially filled

b) valence band are fully filled and conduction band are partially empty

c) valence and are fully filled

d) conduction band are fully empty



Q10 The probability of electrons to be found in the conduction band of an intrinsic semiconductor at a finite temperature :-


a) Decreases exponentially with increasing band gap.

b) Increases exponentially with increasing band gap.

c) Decrease with increasing temperature.

d) Is independent of the temperature and the band gap.



Q11 Choose the false statement from the following :-


a) The resistivity of a semiconductor increases with increase in temperature.

b) Substances with energy gap of the order of 10 eV are insulators.

c) In conductors the valence and conduction bands may over lap.

d) The conductivity of a semiconductor increases with increases in temperature.



Q12 Region which have no free electrons and holes in a p-n junction is :-


a) p – region

b) n - region

c) junction

d) depletion region



Q13 In p-n junction at the near at junction there are :-


a) Positive Ions

b) Negative Ions

c) Positive and negative Ions

d) Electrons and holes



Q14 Depletion layer in p-n junction region is caused by.


a) drift holes

b) diffusion of free carriers

c) migration of impurity ions

d) drift of electrons



Q15 The minority current in a p-an junction is :-


a) from the n-side to the p-side

b) from the n-side to the n-side

c) from the n-side to the p-side if the junction is forward-biased and in the opposite direction if it is reverse biased.

d) from the p-side to the n-side if the junction is forward-biased and in the opposite direction if it is reverse biased.



Q16 The majority current in a p-n junction :-


a) from the n-side to the p-side

b) from the p-side to the n-side

c) from the n-side to the p-side if the junction is forward-biased and in the opposite direction if it is reverse biased

d) from the p-side to the n-side if the junction is forward-biased and in the opposite direction if it is reverse biased



Q17 In a ................. biased P-N junction, the net flow holes is from N-region to the P-region :-


a) F.B.

b) R.B.

c) Unbiased

d) Both 1 & 2



Q18 The resistance of reverse-biased PN junction is about:-


a) 1 ohm

b) 100 ohm

c) 1000 ohm

d) 1000000 ohm



Q19 In a unbias p-n junction :-


a) high potential is at n side and low potential is at p side.

b) high potential is at p side and low potential is at n side.

c) p and n both are at same potential.

d) undetermined.



Q20 Correct statement for diode is :-


a) in full wave rectifier both diodes work alternatively.

b) in full wave rectifier both diodes work simultaneously.

c) efficiency of full wave rectifier and half wave rectifier is same.

d) full wave rectifier in bidirectional.



Q21 The efficiency of half-wave rectifier is about


a) 80 %

b) 40%

c) 60%

d) 20%



Q22 In a transistor :-


a) the emitter has the least concentration of impurity.

b) the collector has the least concentration of impurity.

c) the base has the least concentration of impurity.

d) all the three regions have equal concentration of impurity.



Q23 Which of the following current must be zero in an unbiased P.N. junction diode :-


a) Current due to majority charge carriers (both electrons and holes)

b)Current due to minority charge carriers (both electrons and holes)

c) Current due to majority & minority charge carriers

d) Current due to majority and minority charge carriers (only holes)



Q24 In a n-type semiconductor, which of the following statement is true :-


a) Holes are majority carriers and trivalent atoms are dopants.

b) Electrons are minority carriers and trivalent atoms re dopants.

c) Electrons are minority carriers and pantavalent atoms are dopants.

d) Holes are minority carriers and pentavalent atoms are dopants.



Q25The barrier potential of a p-n junction depends on:-

(a) type of semiconductor material

(b) amount of doping

(c)temperature

Which one of the following is correct ?


a) a and b only

b) b only

c) b and c only

d) a, b and c



Q26 Assertion :- Generally semiconductors do not obey Ohm’s law.

Reason :- Electric current is determined by the rate of flow of charge carriers.


a) A

b) B

c) C

d) D



Q27 Assertion :- Germanium is preferred over silicon for making semiconductor devices.

Reason :- Energy gap for Ge is more than that of Si.


a) A

b) B

c) C

d) D



Q28 Assertion :- If the temperature of a semiconductor is increased, its resistance decreases.

Reason :- The energy gap between conduction band and valence band in case of semiconductor is small.


a) A

b) B

c) C

d) D



Q29 Assertion :- Conductivity of a semiconductor increases on doping.

Reason :- Doping raises the temperature of semiconductor.


a) A

b) B

c) C

d) D



Q30 Assertion :- For a given applied voltage, conduction current in n-type semiconductor is more than that in p-type semiconductor.

Reason :- Mobility of electrons is greater than that of holes.


a) A

b) B

c) C

d) D



Q31 Assertion :- In an unbiased p-n junction, holes diffuse from the p-region to n-region.

Reason :- Hole concentration in p-region is more as compared to n-region.


a) A

b) B

c) C

d) D



Q32 Assertion :- Two p-n junction diodes placed back to back, will work as an n-p n transistor.

Reason :­- The p-region of two p-n junction diodes back to will form the base of n-p-n transistor.


a) A

b) B

c) C

d) D



Q33 Assertion :- A p-n junction with reverser bias can be used as a photo-diode to measure light intensity.

Reason :- In a reverse bias condition the current is small and it is more sensitive to changes in incident light intensity.


a) A

b) B

c) C

d) D



Q34 Assertion :- Metals are better conductor than semiconductors.

Reason :- Valence band and conduction band have large energy gap in case of metals.


a) A

b) B

c) C

d) D



Q35 Assertion :- Photodiode always works under reverse bias condition.

Reason :- It is easier to detect current changes in reverse bias.


a) A

b) B

c) C

d) D







ANSWERS


1) b

2) c

3) c

4) b

5) a

6) b

7) c

8) a

9) a

10) a

11) a

12) d

13) c

14) b

15) a

16) b

17) b

18) d

19) a

20) a

21) b

22) c

23) c

24) d

25) d

26) b

27) d

28) a

29) c

30) a

31) a

32) d

33) a

34) c

35) a


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