76. Some unknown material has a conductivity of 10⁶ mho/m and a permeability of 4 π × 10^–7 H/m. The skin depth for the material at 1 GHz is—

1. 1. 15.9 µm

   
   
   

   2. 20.9 µm

   
   
   

   3. 25.9 µm

   
   
   

   4. 30.9 µm

   
   
   

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1. View Hint View Answer Discuss in Forum

   From the synopsis provided skin depth is given by relation
   

   δ =	1
   	√∏fμσ

   
   

   δ =	1
   	√∏ + 109 + 106 × 4∏ × 10-7

   
   = 15.9 μm
   

   Correct Option: A

   From the synopsis provided skin depth is given by relation
   

   δ =	1
   	√∏fμσ

   
   

   δ =	1
   	√∏ + 109 + 106 × 4∏ × 10-7

   
   = 15.9 μm
   

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77. A short transmission line is represented as follows. The assumption made is—
    

1. 1. A low loss line

   
   
   

   2. A low pass filter

   
   
   

   3. An infinite line

   
   
   

   4. A low loss line at high frequency

   
   
   

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1. View Hint View Answer Discuss in Forum

   Acts as a low loss line at high frequency.

   Correct Option: D

   Acts as a low loss line at high frequency.

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78. Assuming the velocity of EM waves reaching an antenna as 3 × 10⁸ m/sec the length of a half wave dipole antenna required to receive a 5 MHz radio signal is—

1. 1. 7.5 m

   
   
   

   2. 13 m

   
   
   

   3. 30 m

   
   
   

   4. 60 m

   
   
   

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1. View Hint View Answer Discuss in Forum

   We have effective length as leffe =	1
   	2

   
   where l is the actual length of uniform current wave for λ/2 antenna (half wave dipole)
   

   λ	=	3 × 108	= 30 m;      l = leffe × 2 = 60
   2		5 × 2 × 108

   Correct Option: D

   We have effective length as leffe =	1
   	2

   
   where l is the actual length of uniform current wave for λ/2 antenna (half wave dipole)
   

   λ	=	3 × 108	= 30 m;      l = leffe × 2 = 60
   2		5 × 2 × 108

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79. The equation for distortionless transmission if R/ G = L/ C. To attain it, in a line—

1. 1. Of all the parameters, it is best to increase L for distortionless transmission

   
   
   

   2. Keeping R and L constant it is preferrable to increase or decrease G and C

   
   
   

   3. The inductance can be added at any interval

   
   
   

   4. The inductance can be of any value

   
   
   

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1. View Hint View Answer Discuss in Forum

   It is best to increase L for distortionless transmission.

   Correct Option: A

   It is best to increase L for distortionless transmission.

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80. The input impedance of a short circuited quarter wave long transmission line is—

1. 1. Purely reactive

   
   
   

   2. Purely resistive

   
   
   

   3. Dependent on the characteristic impedance of the line

   
   
   

   4. None of the above

   
   
   

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1. View Hint View Answer Discuss in Forum

   ∮ H· dl = 3 | + 2 | – | = 4 |

   Correct Option: D

   ∮ H· dl = 3 | + 2 | – | = 4 |

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