Students can go through AP Inter 2nd Year Physics Notes 11th Lesson Electromagnetic Waves will help students in revising the entire concepts quickly.

## AP Inter 2nd Year Physics Notes 11th Lesson Electromagnetic Waves

→ Displacement current is defined as the current which arises due to time rate of change of electric flux in some part of the electric circuit.

→ E.M waves consist of sinusoildally time varying electric and magnetic fields acting at right angles to each other as well as at right angles to the direction of propagation of waves.

→ Electromagnetic waves were theoritically predicated by Maxwell.

→ Maxwell modified Ampere’s circuital law.

→ Maxwell’s equations are mathematical expressions of Gauss law in electrostatics, Gauss law in magnetism, Faraday’s laws of electromagnetic induction and Ampere’s circuital laws.

→ Hertz and other scientists produced and studied the E.M waves experimentally.

→ Electromagnetic waves are transverse in nature.

→ Velocity of E.M waves is equal to velocity of light.

→ Electromagnetic waves are produced by accelerated charges.

→ The whole range of frequency (or) wavelength of the E.M waves is known as electromagnetic spectrum.

Formulae

→ Displacement current (I_{D}) = ε_{0} \(\frac{\mathrm{d} \phi_{\mathrm{E}}}{\mathrm{dt}}\)

→ Modified Ampere circuital law

\(\oint \overrightarrow{\mathrm{B}} \cdot \overrightarrow{\mathrm{d}} l=\mu_0\left(\mathrm{i}_0+\varepsilon_0 \frac{\mathrm{d} \phi_{\mathrm{E}}}{\mathrm{dt}}\right)\)

→ Maxwell’s equations are

- \(\oint \overrightarrow{\mathrm{E}} \cdot \overrightarrow{\mathrm{d} s}\) = q/ε
_{0}(Gauss law in electrostatics) - \(\oint \overrightarrow{\mathrm{B}} \cdot \overrightarrow{\mathrm{d}} \mathrm{s}\) = 0 (Gauss law in magnetism)
- \(\oint \overrightarrow{\mathrm{E}} \cdot \overrightarrow{\mathrm{d}} l=\frac{-\mathrm{d} \phi_{\mathrm{B}}}{\mathrm{dt}}\) (Faraday’s law of elctromagnetic induction)
- \(\oint \overrightarrow{\mathrm{E}} \cdot \overrightarrow{\mathrm{d}} l=\mu_0\left(\mathrm{i}_0+\varepsilon_0 \frac{\mathrm{d} \phi_{\mathrm{E}}}{\mathrm{dt}}\right)\)

→ Velocity of light (C) = \(\frac{1}{\sqrt{\mu_0 \varepsilon_0}}\) = 3 × 10^{8} m/s

→ Refractive index (μ) = \(\frac{C}{V}=\sqrt{\frac{\mu \varepsilon}{\mu_0 \varepsilon_0}}\)

→ Energy density of electric field (U_{E}) = \(\frac{1}{2}\) ε_{0} C E^{2}

→ Energy density of magnetic field (U_{B} = \(\frac{\mathrm{B}^2}{2 \mu_0^2}\)

→ Poynting vector \((\overrightarrow{\mathrm{p}})=\frac{1}{\mu_0}(\overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{B}})\)

→ Intensity of e.m waves (I) = \(\frac{1}{2}\) ε_{0} C E_{0}^{2}

→ Pressure (p) = \(\frac{1}{\mathrm{~A}} \frac{\mathrm{dp}}{\mathrm{dt}}=\frac{\text { Intensity (I) }}{\mathrm{C}}\)