અચુંબકીય માધ્યમમાં ગતિ કરતાં વિદ્યુતચુંબકીય તરંગમાં વિદ્યુતક્ષેત્ર \({E}=20 \cos \left(2 \times 10^{10} {t}-200 {x}\right) \,{V} / {m} \) છે, તો માધ્યમનો ડાઈઈલેક્ટ્રિક અચળાંક કેટલો હશે? (\(\mu_{{r}}=1\) )

A \(9\)
B \(2\)
C \(\frac{1}{3}\)
D \(3\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(9\)

Step-by-step Solution

Detailed explanation

Speed of wave \(=\frac{2 \times 10^{10}}{200}=10^{8}\, {m} / {s}\) Refractive index \(=\frac{3 \times 10^{8}}{10^{8}}=3\) Now refractive index \(=\sqrt{\varepsilon_{{r}} \mu_{{r}}}\) \(3=\sqrt{\varepsilon_{{r}}(1)}\) \(\Rightarrow \varepsilon_{{r}}=9\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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