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Find the critical frequency when the refractive index of the layer is 0.54 and MUF is 9MHz?(a) 0.84MHz(b) 7.57MHz(c) 0.75MHz(d) 8.4MHzI had been asked this question during an online exam.My question comes from Critical Frequency in division Virtual Height, Critical Frequency and Muf of Antennas

Answer»

Correct answer is (b) 7.57MHz

Explanation: REFRACTIVE index \(N=\sqrt{(1-\FRAC{81N_{max}}{f^2})}\)

⇨ \(N_{max}=\frac{(1-n^2)f^2}{81}=\frac{(1-0.54^2)(9×10^6)^2}{81}=0.708 ×10^{12}/cm^3\)

CRITICAL frequency \(f_c=9\sqrt{N \,max} =9\sqrt{0.708 ×10^{12}}=7.57Mhz\)



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