JEE Physics Semiconductor Electronics MCQs Set 27

Answer: (b) \( \pi \)

Explanation:
1. In the common emitter configuration an increase in base current raises the collector current and lowers the collector voltage.
2. So the output voltage is inverted: the phase difference is \( \pi \).

Teacher's Note:
1. T
2. h
3. e
4.
5. c
6. o
7. m
8. m
9. o
10. n
11.
12. e
13. m
14. i
15. t
16. t
17. e
18. r
19.
20. a
21. m
22. p
23. l
24. i
25. f
26. i
27. e
28. r
29.
30. i
31. s
32.
33. a
34. n
35.
36. i
37. n
38. v
39. e
40. r
41. t
42. i
43. n
44. g
45.
46. a
47. m
48. p
49. l
50. i
51. f
52. i
53. e
54. r
55. .
56.
57. T
58. h
59. e
60.
61. c
62. o
63. m
64. m
65. o
66. n
67.
68. b
69. a
70. s
71. e
72.
73. a
74. n
75. d
76.
77. c
78. o
79. m
80. m
81. o
82. n
83.
84. c
85. o
86. l
87. l
88. e
89. c
90. t
91. o
92. r
93.
94. a
95. m
96. p
97. l
98. i
99. f
100. i
101. e
102. r
103. s
104.
105. g
106. i
107. v
108. e
109.
110. n
111. o
112.
113. p
114. h
115. a
116. s
117. e
118.
119. s
120. h
121. i
122. f
123. t
124. .

Answer: (a) 100 Hz

Explanation:
1. A full-wave rectifier produces two output pulses for every cycle of the input.
2. So the ripple frequency is \( 2\times50=100 \) Hz.

Teacher's Note:
1. A
2.
3. h
4. a
5. l
6. f
7. -
8. w
9. a
10. v
11. e
12.
13. r
14. e
15. c
16. t
17. i
18. f
19. i
20. e
21. r
22.
23. k
24. e
25. e
26. p
27. s
28.
29. t
30. h
31. e
32.
33. i
34. n
35. p
36. u
37. t
38.
39. f
40. r
41. e
42. q
43. u
44. e
45. n
46. c
47. y
48. ,
49.
50. w
51. h
52. i
53. l
54. e
55.
56. a
57.
58. f
59. u
60. l
61. l
62. -
63. w
64. a
65. v
66. e
67.
68. r
69. e
70. c
71. t
72. i
73. f
74. i
75. e
76. r
77.
78. d
79. o
80. u
81. b
82. l
83. e
84. s
85.
86. i
87. t
88. .

Answer: (a) 1.01 mA

Explanation:
1. \( \beta=\Delta I_c/\Delta I_b=100 \), so \( \Delta I_b=0.01 \) mA.
2. \( \Delta I_e=\Delta I_c+\Delta I_b=1.01 \) mA.

Teacher's Note:
1. T
2. h
3. e
4.
5. e
6. m
7. i
8. t
9. t
10. e
11. r
12.
13. c
14. u
15. r
16. r
17. e
18. n
19. t
20.
21. i
22. s
23.
24. t
25. h
26. e
27.
28. s
29. u
30. m
31.
32. o
33. f
34.
35. c
36. o
37. l
38. l
39. e
40. c
41. t
42. o
43. r
44.
45. a
46. n
47. d
48.
49. b
50. a
51. s
52. e
53.
54. c
55. u
56. r
57. r
58. e
59. n
60. t
61. s
62. .
63.
64. T
65. h
66. e
67.
68. b
69. a
70. s
71. e
72.
73. c
74. u
75. r
76. r
77. e
78. n
79. t
80.
81. i
82. s
83.
84. o
85. n
86. l
87. y
88.
89. o
90. n
91. e
92.
93. p
94. e
95. r
96. c
97. e
98. n
99. t
100.
101. o
102. f
103.
104. t
105. h
106. e
107.
108. c
109. o
110. l
111. l
112. e
113. c
114. t
115. o
116. r
117.
118. c
119. u
120. r
121. r
122. e
123. n
124. t
125.
126. h
127. e
128. r
129. e
130. .

Answer: (c) \( \mu_e>\mu_h \)

Explanation:
1. Electrons in the conduction band move freely, while holes move by successive jumps of electrons between bound states.
2. Hence electrons are two to three times more mobile than holes, so \( \mu_e>\mu_h \).

Teacher's Note:
1. T
2. h
3. i
4. s
5.
6. i
7. s
8.
9. w
10. h
11. y
12.
13. n
14. -
15. t
16. y
17. p
18. e
19.
20. d
21. e
22. v
23. i
24. c
25. e
26. s
27.
28. a
29. r
30. e
31.
32. f
33. a
34. s
35. t
36. e
37. r
38.
39. t
40. h
41. a
42. n
43.
44. p
45. -
46. t
47. y
48. p
49. e
50.
51. d
52. e
53. v
54. i
55. c
56. e
57. s
58.
59. o
60. f
61.
62. t
63. h
64. e
65.
66. s
67. a
68. m
69. e
70.
71. s
72. i
73. z
74. e
75. .

Answer: (a) 0.99

Explanation:
1. \( h_{FB}=\alpha \) and \( h_{FE}=\beta \).
2. \( \alpha=\dfrac{\beta}{1+\beta}=\dfrac{95}{96}=0.99 \).

Teacher's Note:
1. A
2. l
3. p
4. h
5. a
6.
7. i
8. s
9.
10. a
11. l
12. w
13. a
14. y
15. s
16.
17. s
18. l
19. i
20. g
21. h
22. t
23. l
24. y
25.
26. l
27. e
28. s
29. s
30.
31. t
32. h
33. a
34. n
35.
36. o
37. n
38. e
39.
40. f
41. o
42. r
43.
44. a
45.
46. t
47. r
48. a
49. n
50. s
51. i
52. s
53. t
54. o
55. r
56. .
57.
58. B
59. e
60. t
61. a
62.
63. e
64. q
65. u
66. a
67. l
68.
69. t
70. o
71.
72. 9
73. 5
74.
75. g
76. i
77. v
78. e
79. s
80.
81. a
82. l
83. p
84. h
85. a
86.
87. c
88. l
89. o
90. s
91. e
92.
93. t
94. o
95.
96. 1
97. .

Answer: (c) Holes are minority carriers and pentavalent atoms are the dopants

Explanation:
1. An n-type semiconductor is formed by doping with pentavalent atoms (phosphorus, arsenic).
2. Each dopant atom donates a free electron, so electrons are the majority carriers and holes are the minority carriers.

Teacher's Note:
1. R
2. e
3. m
4. e
5. m
6. b
7. e
8. r
9.
10. N
11.
12. f
13. o
14. r
15.
16. n
17. e
18. g
19. a
20. t
21. i
22. v
23. e
24. :
25.
26. p
27. e
28. n
29. t
30. a
31. v
32. a
33. l
34. e
35. n
36. t
37.
38. d
39. o
40. p
41. a
42. n
43. t
44. ,
45.
46. e
47. l
48. e
49. c
50. t
51. r
52. o
53. n
54.
55. m
56. a
57. j
58. o
59. r
60. i
61. t
62. y
63.
64. c
65. a
66. r
67. r
68. i
69. e
70. r
71. s
72. .
73.
74. T
75. r
76. i
77. v
78. a
79. l
80. e
81. n
82. t
83.
84. d
85. o
86. p
87. a
88. n
89. t
90. s
91.
92. m
93. a
94. k
95. e
96.
97. p
98. -
99. t
100. y
101. p
102. e
103.
104. m
105. a
106. t
107. e
108. r
109. i
110. a
111. l
112. .

Answer: (a) \( n_e=n_h \)

Explanation:
1. In an intrinsic semiconductor each electron that goes into the conduction band leaves behind a hole.
2. Hence the numbers of free electrons and holes are equal.

Teacher's Note:
1. E
2. q
3. u
4. a
5. l
6.
7. n
8. u
9. m
10. b
11. e
12. r
13. s
14.
15. o
16. f
17.
18. e
19. l
20. e
21. c
22. t
23. r
24. o
25. n
26. s
27.
28. a
29. n
30. d
31.
32. h
33. o
34. l
35. e
36. s
37.
38. i
39. s
40.
41. t
42. h
43. e
44.
45. d
46. e
47. f
48. i
49. n
50. i
51. t
52. i
53. o
54. n
55.
56. o
57. f
58.
59. a
60. n
61.
62. i
63. n
64. t
65. r
66. i
67. n
68. s
69. i
70. c
71.
72. s
73. e
74. m
75. i
76. c
77. o
78. n
79. d
80. u
81. c
82. t
83. o
84. r
85. .
86.
87. D
88. o
89. p
90. i
91. n
92. g
93.
94. d
95. i
96. s
97. t
98. u
99. r
100. b
101. s
102.
103. t
104. h
105. i
106. s
107.
108. b
109. a
110. l
111. a
112. n
113. c
114. e
115. .

Answer: (a) the number density of carriers increases (its effect outweighs the decrease in relaxation time)

Explanation:
1. At higher temperature more electrons gain enough energy to cross the band gap, so the carrier density rises rapidly.
2. The relaxation time decreases slightly because of more collisions, but this effect is far smaller than the increase in carriers.

Teacher's Note:
1. I
2. n
3.
4. m
5. e
6. t
7. a
8. l
9. s
10.
11. c
12. o
13. n
14. d
15. u
16. c
17. t
18. i
19. v
20. i
21. t
22. y
23.
24. f
25. a
26. l
27. l
28. s
29.
30. w
31. i
32. t
33. h
34.
35. t
36. e
37. m
38. p
39. e
40. r
41. a
42. t
43. u
44. r
45. e
46.
47. b
48. e
49. c
50. a
51. u
52. s
53. e
54.
55. c
56. a
57. r
58. r
59. i
60. e
61. r
62.
63. d
64. e
65. n
66. s
67. i
68. t
69. y
70.
71. i
72. s
73.
74. f
75. i
76. x
77. e
78. d
79. .
80.
81. I
82. n
83.
84. s
85. e
86. m
87. i
88. c
89. o
90. n
91. d
92. u
93. c
94. t
95. o
96. r
97. s
98.
99. t
100. h
101. e
102.
103. c
104. a
105. r
106. r
107. i
108. e
109. r
110.
111. d
112. e
113. n
114. s
115. i
116. t
117. y
118.
119. r
120. i
121. s
122. e
123. s
124.
125. e
126. x
127. p
128. o
129. n
130. e
131. n
132. t
133. i
134. a
135. l
136. l
137. y
138. .

Answer: (a) \( E_{G1}<E_{G2}<E_{G3} \)

Explanation:
1. In conductors the bands overlap or the gap is negligible.
2. Semiconductors have a small gap (about 1 eV) and insulators a large gap (more than about 3 eV).
3. So \( E_{G1}<E_{G2}<E_{G3} \).

Teacher's Note:
1. T
2. h
3. e
4.
5. s
6. i
7. z
8. e
9.
10. o
11. f
12.
13. t
14. h
15. e
16.
17. g
18. a
19. p
20.
21. d
22. e
23. c
24. i
25. d
26. e
27. s
28.
29. h
30. o
31. w
32.
33. e
34. a
35. s
36. i
37. l
38. y
39.
40. e
41. l
42. e
43. c
44. t
45. r
46. o
47. n
48. s
49.
50. r
51. e
52. a
53. c
54. h
55.
56. t
57. h
58. e
59.
60. c
61. o
62. n
63. d
64. u
65. c
66. t
67. i
68. o
69. n
70.
71. b
72. a
73. n
74. d
75. .
76.
77. C
78. o
79. n
80. d
81. u
82. c
83. t
84. o
85. r
86. s
87.
88. h
89. a
90. v
91. e
92.
93. t
94. h
95. e
96.
97. s
98. m
99. a
100. l
101. l
102. e
103. s
104. t
105.
106. g
107. a
108. p
109.
110. a
111. n
112. d
113.
114. i
115. n
116. s
117. u
118. l
119. a
120. t
121. o
122. r
123. s
124.
125. t
126. h
127. e
128.
129. l
130. a
131. r
132. g
133. e
134. s
135. t
136. .

Answer: (b) P is a conductor and Q is a semiconductor

Explanation:
1. For metals the resistance rises with temperature (positive temperature coefficient).
2. For semiconductors the resistance falls with temperature (negative temperature coefficient).

Teacher's Note:
1. T
2. e
3. m
4. p
5. e
6. r
7. a
8. t
9. u
10. r
11. e
12.
13. d
14. e
15. p
16. e
17. n
18. d
19. e
20. n
21. c
22. e
23.
24. o
25. f
26.
27. r
28. e
29. s
30. i
31. s
32. t
33. a
34. n
35. c
36. e
37.
38. i
39. s
40.
41. a
42.
43. s
44. i
45. m
46. p
47. l
48. e
49.
50. t
51. e
52. s
53. t
54.
55. t
56. o
57.
58. d
59. i
60. s
61. t
62. i
63. n
64. g
65. u
66. i
67. s
68. h
69.
70. m
71. e
72. t
73. a
74. l
75. s
76.
77. f
78. r
79. o
80. m
81.
82. s
83. e
84. m
85. i
86. c
87. o
88. n
89. d
90. u
91. c
92. t
93. o
94. r
95. s
96. .

Answer: (b) 7/5

Explanation:
1. \( I=nAev_d \), so \( I_e/I_h=(n_e/n_h)(v_e/v_h) \).
2. \( \dfrac74=\dfrac{n_e}{n_h}\times\dfrac54 \), so \( n_e/n_h=7/5 \).

Teacher's Note:
1. C
2. u
3. r
4. r
5. e
6. n
7. t
8.
9. i
10. s
11.
12. p
13. r
14. o
15. p
16. o
17. r
18. t
19. i
20. o
21. n
22. a
23. l
24.
25. t
26. o
27.
28. c
29. a
30. r
31. r
32. i
33. e
34. r
35.
36. c
37. o
38. n
39. c
40. e
41. n
42. t
43. r
44. a
45. t
46. i
47. o
48. n
49.
50. t
51. i
52. m
53. e
54. s
55.
56. d
57. r
58. i
59. f
60. t
61.
62. v
63. e
64. l
65. o
66. c
67. i
68. t
69. y
70. .
71.
72. C
73. a
74. n
75. c
76. e
77. l
78.
79. t
80. h
81. e
82.
83. c
84. o
85. m
86. m
87. o
88. n
89.
90. f
91. a
92. c
93. t
94. o
95. r
96. s
97.
98. o
99. f
100.
101. a
102. r
103. e
104. a
105.
106. a
107. n
108. d
109.
110. c
111. h
112. a
113. r
114. g
115. e
116. .

Answer: (b) the resistance of copper will decrease while that of germanium will increase

Explanation:
1. Copper is a metal: the lattice vibrations reduce on cooling, so its resistance decreases.
2. Germanium is a semiconductor: fewer carriers are excited on cooling, so its resistance increases.

Teacher's Note:
1. M
2. e
3. t
4. a
5. l
6. s
7.
8. i
9. m
10. p
11. r
12. o
13. v
14. e
15.
16. t
17. h
18. e
19. i
20. r
21.
22. c
23. o
24. n
25. d
26. u
27. c
28. t
29. i
30. v
31. i
32. t
33. y
34.
35. w
36. i
37. t
38. h
39.
40. c
41. o
42. o
43. l
44. i
45. n
46. g
47. ,
48.
49. w
50. h
51. i
52. l
53. e
54.
55. s
56. e
57. m
58. i
59. c
60. o
61. n
62. d
63. u
64. c
65. t
66. o
67. r
68. s
69.
70. w
71. o
72. r
73. s
74. e
75. n
76. .

Answer: (d) increases with a rise in its temperature

Explanation:
1. Heating creates more electron-hole pairs, increasing the number of charge carriers.
2. The conductivity therefore increases with temperature.

Teacher's Note:
1. T
2. h
3. i
4. s
5.
6. i
7. s
8.
9. t
10. h
11. e
12.
13. o
14. p
15. p
16. o
17. s
18. i
19. t
20. e
21.
22. o
23. f
24.
25. t
26. h
27. e
28.
29. b
30. e
31. h
32. a
33. v
34. i
35. o
36. u
37. r
38.
39. o
40. f
41.
42. m
43. e
44. t
45. a
46. l
47. s
48.
49. a
50. n
51. d
52.
53. i
54. s
55.
56. t
57. h
58. e
59.
60. d
61. e
62. f
63. i
64. n
65. i
66. n
67. g
68.
69. p
70. r
71. o
72. p
73. e
74. r
75. t
76. y
77.
78. o
79. f
80.
81. s
82. e
83. m
84. i
85. c
86. o
87. n
88. d
89. u
90. c
91. t
92. o
93. r
94. s
95. .

Answer: (a) phosphorus and boron respectively

Explanation:
1. Phosphorus is pentavalent and gives n-type silicon.
2. Boron is trivalent and gives p-type silicon.

Teacher's Note:
1. P
2. h
3. o
4. s
5. p
6. h
7. o
8. r
9. u
10. s
11.
12. h
13. a
14. s
15.
16. f
17. i
18. v
19. e
20.
21. v
22. a
23. l
24. e
25. n
26. c
27. e
28.
29. e
30. l
31. e
32. c
33. t
34. r
35. o
36. n
37. s
38. ,
39.
40. b
41. o
42. r
43. o
44. n
45.
46. h
47. a
48. s
49.
50. t
51. h
52. r
53. e
54. e
55. .
56.
57. T
58. h
59. e
60.
61. f
62. i
63. r
64. s
65. t
66.
67. c
68. r
69. e
70. a
71. t
72. e
73. s
74.
75. f
76. r
77. e
78. e
79.
80. e
81. l
82. e
83. c
84. t
85. r
86. o
87. n
88. s
89. ,
90.
91. t
92. h
93. e
94.
95. s
96. e
97. c
98. o
99. n
100. d
101.
102. c
103. r
104. e
105. a
106. t
107. e
108. s
109.
110. h
111. o
112. l
113. e
114. s
115. .

Answer: (c) \( 1.0\times10^{15}\ \text{cm}^{-3} \)

Explanation:
1. Acceptor density \( =5\times10^{28}/(5\times10^7)=10^{21} \) atoms per m\(^3\).
2. In cm\(^{-3}\): \( 10^{21}\times10^{-6}=10^{15} \).

Teacher's Note:
1. D
2. i
3. v
4. i
5. d
6. e
7.
8. t
9. h
10. e
11.
12. h
13. o
14. s
15. t
16.
17. d
18. e
19. n
20. s
21. i
22. t
23. y
24.
25. b
26. y
27.
28. t
29. h
30. e
31.
32. d
33. i
34. l
35. u
36. t
37. i
38. o
39. n
40.
41. r
42. a
43. t
44. i
45. o
46. ,
47.
48. t
49. h
50. e
51. n
52.
53. c
54. o
55. n
56. v
57. e
58. r
59. t
60.
61. c
62. u
63. b
64. i
65. c
66.
67. m
68. e
69. t
70. r
71. e
72. s
73.
74. t
75. o
76.
77. c
78. u
79. b
80. i
81. c
82.
83. c
84. e
85. n
86. t
87. i
88. m
89. e
90. t
91. r
92. e
93. s
94.
95. b
96. y
97.
98. m
99. u
100. l
101. t
102. i
103. p
104. l
105. y
106. i
107. n
108. g
109.
110. b
111. y
112.
113. 1
114. 0
115.
116. t
117. o
118.
119. t
120. h
121. e
122.
123. m
124. i
125. n
126. u
127. s
128.
129. 6
130. .

Answer: (b) intrinsic

Explanation:
1. Conductivity from thermally broken covalent bonds produces equal numbers of electrons and holes.
2. This is intrinsic conductivity of a pure semiconductor.

Teacher's Note:
1. E
2. x
3. t
4. r
5. i
6. n
7. s
8. i
9. c
10.
11. c
12. o
13. n
14. d
15. u
16. c
17. t
18. i
19. v
20. i
21. t
22. y
23.
24. c
25. o
26. m
27. e
28. s
29.
30. f
31. r
32. o
33. m
34.
35. a
36. d
37. d
38. e
39. d
40.
41. i
42. m
43. p
44. u
45. r
46. i
47. t
48. i
49. e
50. s
51. ,
52.
53. w
54. h
55. i
56. l
57. e
58.
59. i
60. n
61. t
62. r
63. i
64. n
65. s
66. i
67. c
68.
69. c
70. o
71. n
72. d
73. u
74. c
75. t
76. i
77. v
78. i
79. t
80. y
81.
82. c
83. o
84. m
85. e
86. s
87.
88. f
89. r
90. o
91. m
92.
93. t
94. h
95. e
96.
97. p
98. u
99. r
100. e
101.
102. m
103. a
104. t
105. e
106. r
107. i
108. a
109. l
110. .

Answer: (a) is low at high and low frequencies and constant at mid frequencies

Explanation:
1. At low frequencies the coupling and bypass capacitors reduce the gain.
2. At high frequencies the junction capacitances reduce the gain.
3. So the gain is constant only in the mid-frequency range.

Teacher's Note:
1. T
2. h
3. e
4.
5. g
6. a
7. i
8. n
9. -
10. f
11. r
12. e
13. q
14. u
15. e
16. n
17. c
18. y
19.
20. c
21. u
22. r
23. v
24. e
25.
26. o
27. f
28.
29. a
30. n
31.
32. a
33. m
34. p
35. l
36. i
37. f
38. i
39. e
40. r
41.
42. i
43. s
44.
45. f
46. l
47. a
48. t
49.
50. i
51. n
52.
53. t
54. h
55. e
56.
57. m
58. i
59. d
60. d
61. l
62. e
63.
64. a
65. n
66. d
67.
68. f
69. a
70. l
71. l
72. s
73.
74. o
75. n
76.
77. b
78. o
79. t
80. h
81.
82. s
83. i
84. d
85. e
86. s
87. .

Answer: (b) 100 V

Explanation:
1. For half-wave rectification \( V_{rms}=V_0/2 \).
2. \( V_{rms}=200/2=100 \) V.

Teacher's Note:
1. F
2. o
3. r
4.
5. a
6.
7. f
8. u
9. l
10. l
11.
12. s
13. i
14. n
15. e
16.
17. w
18. a
19. v
20. e
21.
22. t
23. h
24. e
25.
26. r
27. m
28. s
29.
30. v
31. a
32. l
33. u
34. e
35.
36. i
37. s
38.
39. p
40. e
41. a
42. k
43.
44. o
45. v
46. e
47. r
48.
49. r
50. o
51. o
52. t
53.
54. t
55. w
56. o
57. ,
58.
59. b
60. u
61. t
62.
63. h
64. a
65. l
66. f
67. -
68. w
69. a
70. v
71. e
72.
73. r
74. e
75. c
76. t
77. i
78. f
79. i
80. c
81. a
82. t
83. i
84. o
85. n
86.
87. g
88. i
89. v
90. e
91. s
92.
93. p
94. e
95. a
96. k
97.
98. o
99. v
100. e
101. r
102.
103. t
104. w
105. o
106. .

Answer: (a) 50 Hz

Explanation:
1. A half-wave rectifier passes one pulse per input cycle.
2. Hence the ripple has the same frequency as the input, 50 Hz.

Teacher's Note:
1. C
2. o
3. m
4. p
5. a
6. r
7. e
8.
9. w
10. i
11. t
12. h
13.
14. t
15. h
16. e
17.
18. f
19. u
20. l
21. l
22. -
23. w
24. a
25. v
26. e
27.
28. r
29. e
30. c
31. t
32. i
33. f
34. i
35. e
36. r
37. ,
38.
39. w
40. h
41. e
42. r
43. e
44.
45. t
46. h
47. e
48.
49. r
50. i
51. p
52. p
53. l
54. e
55.
56. f
57. r
58. e
59. q
60. u
61. e
62. n
63. c
64. y
65.
66. i
67. s
68.
69. t
70. w
71. i
72. c
73. e
74.
75. t
76. h
77. e
78.
79. i
80. n
81. p
82. u
83. t
84.
85. f
86. r
87. e
88. q
89. u
90. e
91. n
92. c
93. y
94. .

Answer: (d) 2.0 V

Explanation:
1. Total gain of the cascade \( =10\times20=200 \).
2. Output \( =200\times0.01=2.0 \) V.

Teacher's Note:
1. I
2. n
3.
4. a
5.
6. c
7. a
8. s
9. c
10. a
11. d
12. e
13.
14. t
15. h
16. e
17.
18. g
19. a
20. i
21. n
22. s
23.
24. m
25. u
26. l
27. t
28. i
29. p
30. l
31. y
32. ,
33.
34. n
35. o
36. t
37.
38. a
39. d
40. d
41. .
42.
43. I
44. n
45.
46. d
47. e
48. c
49. i
50. b
51. e
52. l
53. s
54.
55. t
56. h
57. e
58. y
59.
60. w
61. o
62. u
63. l
64. d
65.
66. a
67. d
68. d
69. .