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JEE Mains · Physics · STD 12 - Electromagnetic waves
  • JEE Mains 2020
  • Medium
  • Numerical

Suppose that intensity of a laser is \(\left(\frac{315}{\pi}\right)\, W / m ^{2} .\) The \(rms\) electric field, in units of \(V / m\) associated with this source is close to the nearest integer is \(\left(\epsilon_{0}=8.86 \times 10^{-12} C ^{2} Nm ^{-2} ; c =3 \times 10^{8} ms ^{-1}\right)\)

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Answer & Solution

Correct Answer

(C) \(194\)

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Detailed explanation

\(I =\epsilon_{0} E _{ rms }^{2} C\)

\(E _{ rms }^{2}=\frac{ I }{\epsilon_{0} C }\)

\(=\frac{315}{\pi \epsilon_{0}} \times \frac{1}{ C }\)

\(=\frac{4 \times 315}{4 \pi \epsilon_{0}} \times \frac{1}{3 \times 10^{8}}\)

\(=\frac{4 \times 315 \times 9 \times 10^{9}}{3 \times 10^{8}}\)

\(E _{ rms }^{2}=4 \times 315 \times 30\)

\(E _{ rms }=2 \sqrt{315 \times 30}\)

\(=194.42\)

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