236. In the infinite plane y = 6 m there exists a uniform surface charge density of
     

     	1	∏
     	600

     
     μ c/m². The associated electric field strength is—

1. 1. 30 i V/m

   
   
   

   2. 30 j V/m

   
   
   

   3. 30 k V/m

   
   
   

   4. 60 i V/m

   
   
   

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1. View Hint View Answer Discuss in Forum

   The associated electric field strength
   

   
   

   1	=	1	× 10−6 ×	1
   2ε0		600π		2 × 8.85 × 10−12

   
   = 30 kV/m

   Correct Option: C

   The associated electric field strength
   

   
   

   1	=	1	× 10−6 ×	1
   2ε0		600π		2 × 8.85 × 10−12

   
   = 30 kV/m

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237. The electric field strength at a distance point P due to a point charge +q located on the origins is 100 µ V/m if the point charge is now enclosed by a perfectly conducting metal sheet sphere whose centre is at origin then the electric field strength at the point P outside the sphere becomes—

1. 1. Zero

   
   
   

   2. 100 µ V/m

   
   
   

   3. – 100 µ V/m

   
   
   

   4. 50 µ V/m

   
   
   

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1. View Hint View Answer Discuss in Forum

   Charge +q induces negative charge inside the sphere and positive charge on the outside of sphere. If the sphere is enclosed by a Gaussian sphere the field strength E will be given by Gauss's law
   

   E =	1	Q
   	4πε0	R2

   
   where R is radius of sphere and Q is total charge. This is same although the charge is present at the origin of sphere. Therefore + 100 µ V/m.

   Correct Option: B

   Charge +q induces negative charge inside the sphere and positive charge on the outside of sphere. If the sphere is enclosed by a Gaussian sphere the field strength E will be given by Gauss's law
   

   E =	1	Q
   	4πε0	R2

   
   where R is radius of sphere and Q is total charge. This is same although the charge is present at the origin of sphere. Therefore + 100 µ V/m.

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238. For a short wave radio link between two stations via the ionosphere. The ratio of the maximum usable frequency to the critical frequency—

1. 1. Is always less than 1

   
   
   

   2. Is always greater than 1

   
   
   

   3. May be less than or more than 1 depending on the distance between the two stations

   
   
   

   4. Does not depend on the distance between the two stations
      

   
   
   

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1. View Hint View Answer Discuss in Forum

   Since we know that f_muf = f_c sec i
   so,
   

   fmuf	= sec i > 1
   fc

   
   

   Correct Option: B

   Since we know that f_muf = f_c sec i
   so,
   

   fmuf	= sec i > 1
   fc

   
   

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239. A beam antenna consists of a dipole one reflector and one director. The velocity factor is 0.90 and antenna is to be cut for a frequency of 150 MHz. The length of the dipole will be—

1. 1. 0.4 m

   
   
   

   2. 0.5 m

   
   
   

   3. 0.9 m

   
   
   

   4. 1.2 m

   
   
   

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1. View Hint View Answer Discuss in Forum

   By calculation as follows
   

   λ =	C
   	velocity factor × f

   
   

   λ =	3 ×108
   	0.9 × 150 × 106

   
   = 1.8
   

   Now effective length of dipole =	1	⇒	1.8	= 0.9
   	2		2

   Correct Option: C

   By calculation as follows
   

   λ =	C
   	velocity factor × f

   
   

   λ =	3 ×108
   	0.9 × 150 × 106

   
   = 1.8
   

   Now effective length of dipole =	1	⇒	1.8	= 0.9
   	2		2

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240. Input impedance for the given line is—
     

1. 1. Inductance

   
   
   

   2. Capacitance

   
   
   

   3. Tank circuit

   
   
   

   4. None of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   Graph shows clearly that shorted stub of given length is of capacitive type.

   Correct Option: B

   Graph shows clearly that shorted stub of given length is of capacitive type.

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