# AP Inter 2nd Year Physics Notes Chapter 11 Electromagnetic Waves

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 (ID) = ε0 $$\frac{\mathrm{d} \phi_{\mathrm{E}}}{\mathrm{dt}}$$

→ 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

1. $$\oint \overrightarrow{\mathrm{E}} \cdot \overrightarrow{\mathrm{d} s}$$ = q/ε0 (Gauss law in electrostatics)
2. $$\oint \overrightarrow{\mathrm{B}} \cdot \overrightarrow{\mathrm{d}} \mathrm{s}$$ = 0 (Gauss law in magnetism)
3. $$\oint \overrightarrow{\mathrm{E}} \cdot \overrightarrow{\mathrm{d}} l=\frac{-\mathrm{d} \phi_{\mathrm{B}}}{\mathrm{dt}}$$ (Faraday’s law of elctromagnetic induction)
4. $$\oint \overrightarrow{\mathrm{E}} \cdot \overrightarrow{\mathrm{d}} l=\mu_0\left(\mathrm{i}_0+\varepsilon_0 \frac{\mathrm{d} \phi_{\mathrm{E}}}{\mathrm{dt}}\right)$$

→ Velocity of light (C) = $$\frac{1}{\sqrt{\mu_0 \varepsilon_0}}$$ = 3 × 108 m/s

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

→ Energy density of electric field (UE) = $$\frac{1}{2}$$ ε0 C E2

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

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

→ Intensity of e.m waves (I) = $$\frac{1}{2}$$ ε0 C E02

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