Electromagnetic Waves Class 12 Notes Physics Chapter 8 - CBSE
Chapter : 8
What are Electromagnetic Waves ?
| Topic | Formula | Symbol Representation | Important Points |
| Displacement Current | $$\text{I}_\text{D}= \epsilon_\text{0}\frac{\text{d}\phi_\text{E}}{\text{dt}}\\ \space\space\space\space\space\space\text{or} \\ \frac{\text{dq}}{\text{dt}}=\epsilon_\text{0}\frac{\text{d}\phi}{\text{dt}}$$ | ID = Maxwell’s displacement current Φ = Electric flux (dΦ/dt) = Rate of change of electric flux |
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| Electromagnetic waves | $$\text{c}=\frac{1}{\sqrt{\mu_0\epsilon_0}}\\=3×10^8\text{ms}^{-1}\\ \oint\vec{\text{B}}.\vec{\text{dl}}=\mu_0(\text{I}+\text{I}_\text{D})\\=\mu_0(\text{I}+\frac{\epsilon_0\text{d}\phi_\epsilon}{\text{dt}})\\ (\text{Ampere-Maxwell law}) \\ \oint\vec{\text{E}}\vec{\text{ds}}=\frac{\text{q}}{\epsilon_0}\\ \text{Gauss law in electrostate}$$ $$\oint\vec{\text{B}}.\vec{\text{ds}}=0\\ \text{(Gauss law in magnetostate)} \\ \oint\vec{\text{E}}.\vec{\text{dl}}=\frac{\text{-df}}{\text{dt}}\int_s \vec{\text{B}}\vec{\text{ds}} \\ \text{(Faraday’s law of EM induction)}$$ |
c = speed of light μ0 = permeability constant = 4π × 10-7H/m ε0 = Vacuum permittivity = 8.85 × 10-12C2/N.m2  = magnetic field ∮ = integral over closed path I = conduction current ID = displacement current |
$$\bull\space \text{Electric field} \vec{(\text{E})} \text{and magnetic field} \\\vec{(\text{B})} \text{are at right angle to each other}\\ \space \text{as well as right angle to the}\\ \text{direction of wave propagation}. $$ Example: radio waves, microwaves, infrared waves etc.
$$\bull\space \vec{\text{E}} \space\text{and} \space\vec{\text{B}} \space\text{are in same phase (in EM)}. $$ $$\space \vec{\text{E}} \space\text{and} \space\vec{\text{B}}$$ |
| EM spectrum | |||
