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JEE Mains · Physics · STD 12 - 8. Electromagnetic waves

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)

  1. A \(60\)
  2. B \(6\)
  3. C \(9\)
  4. D \(3\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(6\)

Step-by-step Solution

Detailed explanation

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