Physics · Electromagnetic Waves

JEE Main 2026 — 21 January, Evening Shift — Question 43

An electromagnetic wave of frequency 100 MHz propagates through a medium of conductivity, σ=10mho/m\sigma=10 \mathrm{mho} / \mathrm{m}. The ratio of maximum conducting current density to maximum displacement current density is ____\_\_\_\_。 [\left[\right. Take 14πϵ0=9×109Nm2/C2]\left.\frac{1}{4 \pi \epsilon_{0}}=9 \times 10^{9} \mathrm{Nm}^{2} / \mathrm{C}^{2}\right]

Answer: 1800

Numerical answer — enter this value.

Step-by-step solution

jc=σE\mathrm{j}_{\mathrm{c}}=\sigma \mathrm{E} E⇒E0sin⁡(ωt−kx)\mathrm{E} \Rightarrow \mathrm{E}_{0} \sin (\omega \mathrm{t}-\mathrm{kx}) jc=σE0sin⁡(ωt−kx)\mathrm{j}_{\mathrm{c}}=\sigma \mathrm{E}_{0} \sin (\omega \mathrm{t}-\mathrm{kx}) ⇒(jc)max =σE0\begin{gathered} \Rightarrow\left(\mathrm{j}_{\mathrm{c}}\right)_{\text {max }}=\sigma \mathrm{E}_{0} \end{gathered} Jd⇒idA=1 A×ε0AdEdt\mathrm{J}_{\mathrm{d}} \Rightarrow \frac{\mathrm{i}_{\mathrm{d}}}{\mathrm{A}}=\frac{1}{\mathrm{~A}} \times \varepsilon_{0} \frac{\mathrm{AdE}}{\mathrm{dt}} ⇒ε0×E0ωcos⁡(ωt−kx)\Rightarrow \varepsilon_{0} \times \mathrm{E}_{0} \omega \cos (\omega \mathrm{t}-\mathrm{kx}) (jd)max ⇒ε0E0ω\begin{gathered} \left(\mathrm{j}_{\mathrm{d}}\right)_{\text {max }} \Rightarrow \varepsilon_{0} \mathrm{E}_{0} \omega \end{gathered} (i)/(ii) (jc)max (jd)max =σE0ε0ωE0⇒σε0ω\frac{\left(\mathrm{j}_{\mathrm{c}}\right)_{\text {max }}}{\left(\mathrm{j}_{\mathrm{d}}\right)_{\text {max }}}=\frac{\sigma \mathrm{E}_{0}}{\varepsilon_{0} \omega \mathrm{E}_{0}} \Rightarrow \frac{\sigma}{\varepsilon_{0} \omega} ⇒10×4π×9×1092π×100×106\Rightarrow \frac{10 \times 4 \pi \times 9 \times 10^{9}}{2 \pi \times 100 \times 10^{6}} ⇒1800\Rightarrow 1800

Answer key and solution verified before publishing.

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Exam
JEE Main 2026
Subject
Physics
Chapter
Electromagnetic Waves
Topic
Displacement Current and Equation of EM Waves