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Help me please, Long range radio transmission is possible when the radiowaves are reflected from the ionosphere. For this to happen thefrequency of the radiowaves must be in the range :

 Long range radio transmission is possible when the radiowaves are reflected from the ionosphere. For this to happen the   
frequency of the radiowaves must be in the range :        

 

  • Option 1)

     80 - 150 MHz   
     

  • Option 2)

      8 - 25 MHz   
     

  • Option 3)

    1 - 3 MHz   
     

  • Option 4)

    150 - 500 kHz   

 
Answers (1)
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As we have learnt,

 

Value of critical frequency -

f_{c}= 9.\left ( N_{max} \right )^{1/2}

 

- wherein

Nmax is maximum electron density of the ionosphere in per m3 .

 

 For reflection to happen from ionosphere frequency should be less than critical frequency 

f \leq f_C

f_C = 9\sqrt{N_{max}}

       \approx 30 MHz

\therefore Frequency should be less than than 30 MHz


Option 1)

 80 - 150 MHz   
 

Option 2)

  8 - 25 MHz   
 

Option 3)

1 - 3 MHz   
 

Option 4)

150 - 500 kHz   

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