JEE Main 2022 · 24 Jun · Shift 2 · Physics Q52

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An antenna is placed in a dielectric medium of dielectric constant 6.25. If the maximum size of that antenna is 5.0 mm, it can radiate a signal of minimum frequency of ______ GHz.

(Given $\mu_r=1$ for dielectric medium)

Your answer

Answer and worked solution

Official answer: 6

Speed in the medium. $v=\dfrac c{\sqrt{\varepsilon_r\mu_r}}=\dfrac{3\times10^8}{2.5}=1.2\times10^8$ m s $^{-1}$ .

Antenna. Size $\dfrac\lambda4=5$ mm gives the longest wavelength $\lambda=20$ mm.

Minimum frequency. $f=\dfrac v\lambda=\dfrac{1.2\times10^8}{0.02}=6\times10^9$ Hz $=6$ GHz.

Answer: 6

Topics:Propagation of EM waves Properties of EM waves

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JEE Main 2022 · 24 Jun · Shift 2, Physics question 52