# Electromagnetic Waves Notes, Class 12 Physics | SwaVid

Electromagnetic Waves, NCERT Class 12 Physics: notes with key ideas, formulas, common mistakes and 3 quick checks with worked answers.

Canonical: https://www.swavid.com/cbse/class-12/physics/chapter/electromagnetic-waves

Source: https://www.swavid.com/cbse/class-12/physics/chapter/electromagnetic-waves

# Electromagnetic Waves

## Formulas and definitions

## Key ideas

## Common mistakes

## Quick checks

## Keep going

## Questions parents ask

## Class 12 Physics on SwaVid

### Displacement current

### Source and nature of electromagnetic waves

### Speed and energy transport

### The electromagnetic spectrum

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SwaVid › CBSE › Class 12 › Physics › Electromagnetic Waves

Notes written by SwaVid from the NCERT textbook.

Class 12 Physics, Chapter 8. Key ideas, formulas and common mistakes.

CBSE prints 18 marks for Units V-VI together, not for this chapter alone.

Short answer. This chapter explains how time-varying electric and magnetic fields generate transverse electromagnetic waves that propagate through space without a medium. It shows that Maxwell modified Ampere's circuital law with displacement current and classifies the electromagnetic spectrum by wavelength and frequency.

Source: NCERT Physics Part I (Reprint 2026-27) , Chapter 8, Electromagnetic Waves

Maxwell noticed that Ampere's circuital law was inconsistent for a charging capacitor because conduction current stops at the plates. He introduced displacement current, which is produced by a changing electric flux, making the total current continuous across any closed path.

Accelerated charges produce electromagnetic waves. The electric and magnetic fields oscillate perpendicular to each other and perpendicular to the direction of wave propagation, making the wave transverse.

In free space, electromagnetic waves travel at the speed of light, c = 1 / √(μ₀ ε₀). These waves carry energy and momentum; when absorbed completely by a surface, they deliver momentum p = U / c and exert radiation pressure.

The spectrum spans a wide range of frequencies, classified in order of increasing frequency as radio waves, microwaves, infrared waves, visible light, ultraviolet rays, X-rays, and gamma rays. Each band has distinctive production methods and applications.

Try each question first. Then tap it to see the answer.

Use the relation B₀ = E₀ / c

B₀ = 48 / (3 × 10⁸)

B₀ = 1.6 × 10⁻⁷ T

1.6 × 10⁻⁷ T

Use the formula i d = ε₀ (dΦ E / dt)

i d = 8.85 × 10⁻¹² × 2.0 × 10¹¹

i d = 1.77 A

1.77 A

For complete absorption, momentum p = U / c

p = (1.2 × 10⁻³) / (3 × 10⁸)

p = 4.0 × 10⁻¹² kg m s⁻¹

4.0 × 10⁻¹² kg m s⁻¹

Ray Optics and Optical Instruments .

Electromagnetic Induction .

Wave Optics .

The 14 chapters of Class 12 Physics .

CBSE does not give marks to one chapter. It prints 18 marks for Units V-VI together (Electromagnetic Waves; Optics). Electromagnetic Waves is part of that group.

No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed.

Ray Optics and Optical Instruments.

SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works.

- Ch 8 NCERT book
- 18 marks, Units V-VI together
- 3 quick checks
- Thinking displacement current involves the actual flow of physical charges . Remember that displacement current is purely the rate of change of electric flux scaled by ε₀, not moving electrons.
- Using the relation B₀ = c E₀ instead of E₀ = c B₀ . The electric field amplitude is always much larger in magnitude in SI units than the magnetic field amplitude, so E₀ = c B₀.
- Confusing the momentum delivered by total absorption with that by total reflection . For complete absorption, momentum delivered is p = U / c. For complete reflection, the momentum transferred is doubled, p = 2U / c.

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