RBSE Class 12 Physics Notes Chapter 8 Electromagnetic Waves

These comprehensive RBSE Class 12 Physics Notes Chapter 8 Electromagnetic Waves will give a brief overview of all the concepts.

RBSE Class 12 Physics Chapter 8 Notes Electromagnetic Waves

Electromagnetic Waves:
Displacement current is that current which comes into play in the region on which the electric field and electric flux is changing with time. The displacement current is given by
I_D = ε₀\(\frac{d \phi_e}{d t}\)

Modified form of Ampere’s circuital law:
Maxwell modified Ampere’s circuital law in order to make the law logically consistent. The modified form of Ampere’s circuital law is
∮\(\overrightarrow{\mathrm{B}} . d \vec{l}\) = μ₀(I + I_D) = μ₀(I + ε₀\(\frac{d \phi_e}{d t}\))

Electromagnetic waves:
Electromagnetic waves are those waves in which there are sinusoidal variations of electric and magnetic fields at right angle to each other as well as at right angle to the direction of propagation of the waves e.g. visible light, U.V. rays, IR rays, X-rays, y-rays microwaves, radio waves etc.

Velocity of electromagnetic waves in free space is given as
c = \(\frac{1}{\sqrt{\mu_0 \varepsilon_0}}\)
or
c = \(\frac{1}{\sqrt{4 \pi \times 10^{-7} \times 8.854 \times 10^{-12}}}\) ≈ 3.0 × 10⁸ ms^-1

Production of electromagnetic waves:
An electric charge at rest can produce only electric field and a charge moving with uniform velocity can produce magnetic field. But a charge moving with accelerated motion can produce both electric and magnetic field hence electromagnetic waves can be produced having frequency equal to the frequency of oscillating charge.

An oscillating charge in LC circuit can emit electromagnetic waves.
Electromagnetic waves require no material medium for their propagation and the cross product \(\overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{B}}\) gives the direction of em wave.

Electromagnetic spectrum:

• Electromagnetic spectrum is the orderly distribution of electromagnetic radiations according to their wavelength or frequency.
• Electromagnetic spectrum has very wide range with wavelength variation 10^-14 m to 10⁶ m (or frequency variation 10²² Hz to 10⁴ Hz). A very small part of the spectrum is visible called visible range from 4 × 10^-7 m to 8 × 10^-7 m.
• Electromagnetic waves has a large number of uses.