JEE Physics Communication System MCQs Set 13

Answer: (a) Point-to-point

Explanation:
1. In telephony a message passes between one transmitter and one particular receiver, so it is a point-to-point mode.
2. Radio and television, in contrast, are broadcast modes.

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

Answer: (a) Amplitude modulation

Explanation:
1. Standard AM radio broadcasting uses amplitude modulation, in which the carrier amplitude varies with the message signal.

Teacher's Note:
1. A
2. \( M \)
3.
4. \( i \)
5. \( s \)
6.
7. \( u \)
8. \( s \)
9. \( e \)
10. \( d \)
11.
12. \( f \)
13. \( o \)
14. \( r \)
15.
16. \( m \)
17. \( e \)
18. \( d \)
19. \( i \)
20. \( u \)
21. \( m \)
22. -
23. \( w \)
24. a
25. \( v \)
26. \( e \)
27.
28. \( b \)
29. \( r \)
30. \( o \)
31. a
32. \( d \)
33. \( c \)
34. a
35. \( s \)
36. \( t \)
37. \( s \)
38.
39. a
40. \( n \)
41. \( d \)
42.
43. \( F \)
44. \( M \)
45.
46. \( f \)
47. \( o \)
48. \( r \)
49.
50. \( t \)
51. \( h \)
52. \( e \)
53.
54. \( V \)
55. \( H \)
56. \( F \)
57.
58. \( b \)
59. a
60. \( n \)
61. \( d \)
62. .

Answer: (a) convert the message signal into a form suitable for transmission through the channel

Explanation:
1. The transmitter processes the message signal from the source (modulation, amplification) so that it can be sent through the channel.

Teacher's Note:
1. \( T \)
2. \( h \)
3. \( e \)
4.
5. \( t \)
6. \( h \)
7. \( r \)
8. \( e \)
9. \( e \)
10.
11. \( b \)
12. a
13. \( s \)
14. \( i \)
15. \( c \)
16.
17. \( b \)
18. \( l \)
19. \( o \)
20. \( c \)
21. \( k \)
22. \( s \)
23.
24. a
25. \( r \)
26. \( e \)
27.
28. \( t \)
29. \( r \)
30. a
31. \( n \)
32. \( s \)
33. \( m \)
34. \( i \)
35. \( t \)
36. \( t \)
37. \( e \)
38. \( r \)
39. ,
40.
41. \( c \)
42. \( h \)
43. a
44. \( n \)
45. \( n \)
46. \( e \)
47. \( l \)
48.
49. a
50. \( n \)
51. \( d \)
52.
53. \( r \)
54. \( e \)
55. \( c \)
56. \( e \)
57. \( i \)
58. \( v \)
59. \( e \)
60. \( r \)
61. .

Answer: (a) High or radio frequencies

Explanation:
1. Efficient radiation needs an antenna of size comparable to the wavelength; a 20 kHz signal has a 15 km wavelength.
2. So the baseband signal is translated to high (radio) frequencies by modulation.

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

Answer: (a) resonant

Explanation:
1. A half-wave antenna supports a standing wave and radiates most efficiently at this length.
2. This is the resonant condition.

Teacher's Note:
1. \( R \)
2. \( e \)
3. \( s \)
4. \( o \)
5. \( n \)
6. a
7. \( n \)
8. \( t \)
9.
10. \( l \)
11. \( e \)
12. \( n \)
13. \( g \)
14. \( t \)
15. \( h \)
16.
17. \( g \)
18. \( i \)
19. \( v \)
20. \( e \)
21. \( s \)
22.
23. \( m \)
24. a
25. \( x \)
26. \( i \)
27. \( m \)
28. \( u \)
29. \( m \)
30.
31. \( r \)
32. a
33. \( d \)
34. \( i \)
35. a
36. \( t \)
37. \( i \)
38. \( o \)
39. \( n \)
40.
41. \( e \)
42. \( f \)
43. \( f \)
44. \( i \)
45. \( c \)
46. \( i \)
47. \( e \)
48. \( n \)
49. \( c \)
50. \( y \)
51. .

Answer: (a) modulation

Explanation:
1. Modulation varies a property (amplitude, frequency or phase) of the carrier in accordance with the message signal.

Teacher's Note:
1. \( D \)
2. \( e \)
3. \( m \)
4. \( o \)
5. \( d \)
6. \( u \)
7. \( l \)
8. a
9. \( t \)
10. \( i \)
11. \( o \)
12. \( n \)
13.
14. \( i \)
15. \( s \)
16.
17. \( t \)
18. \( h \)
19. \( e \)
20.
21. \( r \)
22. \( e \)
23. \( v \)
24. \( e \)
25. \( r \)
26. \( s \)
27. \( e \)
28.
29. \( p \)
30. \( r \)
31. \( o \)
32. \( c \)
33. \( e \)
34. \( s \)
35. \( s \)
36.
37. a
38. \( t \)
39.
40. \( t \)
41. \( h \)
42. \( e \)
43.
44. \( r \)
45. \( e \)
46. \( c \)
47. \( e \)
48. \( i \)
49. \( v \)
50. \( e \)
51. \( r \)
52. .

Answer: (b) Optical fibres have extremely low transmission loss

Explanation:
1. Optical fibres carry light by total internal reflection and have very low loss.
2. They are free from external electromagnetic interference.
3. A receiver is tuned by varying the local oscillator or resonant circuit, not the antenna.
4. Digital signals take discrete values.

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

Answer: (a) in the equatorial plane at zero inclination

Explanation:
1. A geostationary satellite must have a period of 24 hours and appear fixed in the sky, so it orbits in the equatorial plane with inclination zero.

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

Answer: (a) ground based vertical towers

Explanation:
1. Medium-wave AM transmission uses vertical towers; the ground has a strong influence on propagation of the ground wave.

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

Answer: (b) 0.5

Explanation:
1. \( m_a = \dfrac{E_{max}-E_{min}}{E_{max}+E_{min}} = \dfrac{90-30}{90+30} = 0.5 \).

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

Answer: (c) Line of sight (space wave)

Explanation:
1. Above about 40 MHz, communication is essentially limited to line-of-sight paths.
2. Waves at 100 MHz are not reflected by the ionosphere and the ground wave attenuates quickly.

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

Answer: (b) normal to the Earth's surface

Explanation:
1. Ground waves are vertically polarised, because a horizontal electric field would be short-circuited by the conducting ground.

Teacher's Note:
1. \( T \)
2. \( h \)
3. \( e \)
4.
5. \( g \)
6. \( r \)
7. \( o \)
8. \( u \)
9. \( n \)
10. \( d \)
11.
12. \( w \)
13. \( o \)
14. \( u \)
15. \( l \)
16. \( d \)
17.
18. \( c \)
19. a
20. \( n \)
21. \( c \)
22. \( e \)
23. \( l \)
24.
25. a
26.
27. \( h \)
28. \( o \)
29. \( r \)
30. \( i \)
31. \( z \)
32. \( o \)
33. \( n \)
34. \( t \)
35. a
36. \( l \)
37.
38. \( e \)
39. \( l \)
40. \( e \)
41. \( c \)
42. \( t \)
43. \( r \)
44. \( i \)
45. \( c \)
46.
47. \( f \)
48. \( i \)
49. \( e \)
50. \( l \)
51. \( d \)
52. .

Answer: (b) is different for different layers of the ionosphere

Explanation:
1. \( f_c = 9\sqrt{N_{max}} \), where \( N_{max} \) is the maximum electron density of the layer.
2. Different layers have different electron densities, so their critical frequencies differ.

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

Answer: (d) all of the above

Explanation:
1. \( D_{skip} = 2h\sqrt{\left(\dfrac{f}{f_c}\right)^2 - 1} \).
2. It depends on the layer height \( h \), the wave frequency \( f \) and the critical frequency \( f_c \).

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

Answer: (d) suppress the carrier component

Explanation:
1. Most of the power of an AM wave is in the carrier, which carries no information.
2. A balanced modulator cancels the carrier, leaving only the sidebands.

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

Answer: (b) \( \dfrac{1}{3} \) of the total power

Explanation:
1. Sideband power \( = \dfrac{m_a^2}{2}P_c \) and total power \( = \left(1+\dfrac{m_a^2}{2}\right)P_c \).
2. For \( m_a = 1 \): ratio \( = \dfrac{1/2}{1+1/2} = \dfrac{1}{3} \).

Teacher's Note:
1. \( E \)
2. \( v \)
3. \( e \)
4. \( n \)
5.
6. a
7. \( t \)
8.
9. 1
10. 0
11. 0
12. %
13.
14. \( m \)
15. \( o \)
16. \( d \)
17. \( u \)
18. \( l \)
19. a
20. \( t \)
21. \( i \)
22. \( o \)
23. \( n \)
24.
25. \( t \)
26. \( w \)
27. \( o \)
28.
29. \( t \)
30. \( h \)
31. \( i \)
32. \( r \)
33. \( d \)
34. \( s \)
35.
36. \( o \)
37. \( f \)
38.
39. \( t \)
40. \( h \)
41. \( e \)
42.
43. \( p \)
44. \( o \)
45. \( w \)
46. \( e \)
47. \( r \)
48.
49. \( i \)
50. \( s \)
51.
52. \( i \)
53. \( n \)
54.
55. \( t \)
56. \( h \)
57. \( e \)
58.
59. \( c \)
60. a
61. \( r \)
62. \( r \)
63. \( i \)
64. \( e \)
65. \( r \)
66. .

Answer: (b) 25%

Explanation:
1. Percent modulation \( = \dfrac{\Delta f_{actual}}{\Delta f_{max}}\times100 = \dfrac{18.75}{75}\times100 = 25\% \).

Teacher's Note:
1. \( F \)
2. \( o \)
3. \( r \)
4.
5. \( F \)
6. \( M \)
7.
8. \( b \)
9. \( r \)
10. \( o \)
11. a
12. \( d \)
13. \( c \)
14. a
15. \( s \)
16. \( t \)
17.
18. \( t \)
19. \( h \)
20. \( e \)
21.
22. \( m \)
23. a
24. \( x \)
25. \( i \)
26. \( m \)
27. \( u \)
28. \( m \)
29.
30. \( p \)
31. \( e \)
32. \( r \)
33. \( m \)
34. \( i \)
35. \( t \)
36. \( t \)
37. \( e \)
38. \( d \)
39.
40. \( d \)
41. \( e \)
42. \( v \)
43. \( i \)
44. a
45. \( t \)
46. \( i \)
47. \( o \)
48. \( n \)
49.
50. \( i \)
51. \( s \)
52.
53. 7
54. 5
55.
56. \( k \)
57. \( H \)
58. \( z \)
59. .

Answer: (b) 54 W

Explanation:
1. Carrier power \( P_c = \dfrac{E_c^2}{2R} = \dfrac{100^2}{2\times100} = 50 W \).
2. \( P = P_c\left(1+\dfrac{m_a^2}{2}\right) = 50\left(1+\dfrac{0.16}{2}\right) = 54 W \).

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

Answer: (d) both (a) and (b)

Explanation:
1. Each modulating frequency gives carrier plus and minus that frequency.
2. 300 Hz: 1000.3 and 999.7 kHz. 800 Hz: 1000.8 and 999.2 kHz. 2 kHz: 1002 and 998 kHz.
3. Options \( (a) \) and \( (b) \) together list all the sideband frequencies, so \( (d) \) is correct.

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

Answer: (c) 6.25

Explanation:
1. Carrier amplitude \( A_c = 10 \), so \( P_c = \dfrac{A_c^2}{2} = 50 \).
2. Total sideband power \( = \dfrac{m_a^2}{2}P_c = \dfrac{0.25}{2}\times50 = 6.25 \).

Teacher's Note:
1. \( E \)
2. a
3. \( c \)
4. \( h \)
5.
6. \( s \)
7. \( i \)
8. \( d \)
9. \( e \)
10. \( b \)
11. a
12. \( n \)
13. \( d \)
14.
15. \( c \)
16. a
17. \( r \)
18. \( r \)
19. \( i \)
20. \( e \)
21. \( s \)
22.
23. \
24. (
25.
26. \( m \)
27. _
28. a
29. \( ^ \)
30. 2
31. \( P \)
32. _
33. \( c \)
34. /
35. 4
36.
37. \
38. )
39. ,
40.
41. \( s \)
42. \( o \)
43.
44. \( t \)
45. \( h \)
46. \( e \)
47.
48. \( p \)
49. a
50. \( i \)
51. \( r \)
52.
53. \( c \)
54. a
55. \( r \)
56. \( r \)
57. \( i \)
58. \( e \)
59. \( s \)
60.
61. \
62. (
63.
64. \( m \)
65. _
66. a
67. \( ^ \)
68. 2
69. \( P \)
70. _
71. \( c \)
72. /
73. 2
74.
75. \
76. )
77. .

Answer: (b) VSB

Explanation:
1. Vestigial side band (VSB) modulation reduces the bandwidth because the same information is present in both sidebands.
2. SSB is not used because it is difficult to remove one sideband completely.

Teacher's Note:
1. \( V \)
2. \( S \)
3. \( B \)
4.
5. \( i \)
6. \( s \)
7.
8. a
9.
10. \( c \)
11. \( o \)
12. \( m \)
13. \( p \)
14. \( r \)
15. \( o \)
16. \( m \)
17. \( i \)
18. \( s \)
19. \( e \)
20.
21. \( b \)
22. \( e \)
23. \( t \)
24. \( w \)
25. \( e \)
26. \( e \)
27. \( n \)
28.
29. \( D \)
30. \( S \)
31. \( B \)
32.
33. a
34. \( n \)
35. \( d \)
36.
37. \( S \)
38. \( S \)
39. \( B \)
40. .

Answer: (d) repeater stations are used

Explanation:
1. A repeater receives the signal, removes noise, amplifies and retransmits it.
2. Repeaters are placed at intermediate points on long paths.

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

Answer: (a) the refractive index of the ionosphere becomes too high for total internal reflection to occur when \( f > f_c \)

Explanation:
1. Total internal reflection requires a sufficiently low refractive index of the ionosphere.
2. For \( f > f_c \) the refractive index rises towards 1, so the wave passes through instead of being reflected.

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

Answer: (a) 1.32

Explanation:
1. \( P_t = P_c\left(1+\dfrac{m_a^2}{2}\right) = 1\times\left(1+\dfrac{0.64}{2}\right) = 1.32 \) kW.

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

Answer: (b) 0.43

Explanation:
1. \( m_a = \dfrac{V_{max}-V_{min}}{V_{max}+V_{min}} = \dfrac{10-4}{10+4} = 0.43 \).

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. \( s \)
14. a
15. \( m \)
16. \( e \)
17.
18. \( r \)
19. \( e \)
20. \( l \)
21. a
22. \( t \)
23. \( i \)
24. \( o \)
25. \( n \)
26.
27. a
28. \( s \)
29.
30. \( f \)
31. \( o \)
32. \( r \)
33.
34. a
35. \( m \)
36. \( p \)
37. \( l \)
38. \( i \)
39. \( t \)
40. \( u \)
41. \( d \)
42. \( e \)
43. \( s \)
44. .