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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

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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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