JEE Mains · Physics · STD 12 - Electromagnetic waves
- JEE Mains 2019
- Medium
- MCQ
A \(27\, mW\) lager beam has a cross -sectional area of \(10\, mm^2\). The magnitude of the maximum electric field in this electromagnetic wave is given by:........\(kV/m\) [Given permittivity of space \({ \in _0} = 9 \times {10^{ - 12}}\, SI\, units\), speed of light \(c = 3 \times 10^8\, m/s\)]
Pick an option to check your answer.
Answer & Solution
Correct Answer
(D) \(1.4\)
Step-by-step Solution
Detailed explanation
Intensity of \(EM\) wave is given by
\({\mathrm{I}=\frac{\text { Power }}{\text { Area }}=\frac{1}{2} \varepsilon_{0} \mathrm{E}_{0}^{2} \mathrm{C}}\)
\({=\frac{27 \times 10^{-3}}{10 \times 10^{-6}}=\frac{1}{2} \times 9 \times 10^{-2} \times \mathrm{E}^{2} \times 3 \times 10^{8}}\)
\({\mathrm{E}=\sqrt{2} \times 10^{3}\, \mathrm{kV} / \mathrm{m}}\)
\({=1.4\, \mathrm{kV} / \mathrm{m}}\)
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