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  4. 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 μ r =1 for dielectric medium)

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Q. 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)

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Solution:

$C^{\prime}=\frac{C}{\sqrt{\mu_{ r } \varepsilon_{ r }}}=\frac{3 \times 10^{8}}{\sqrt{6.25}}=\frac{3 \times 10^{8}}{2.5} $
$f \lambda=1.25 \times 10^{8} s $
$\Rightarrow f \left(5 \times 10^{-3} \times 4\right)=1.25 \times 10^{8}$
$ f =6.25 \,GHz$
So $f \approx 6$