Electromagnetic Waves – Class 12 Physics Notes | Full NCERT Chapter Summary

 🌈 Chapter 8: Electromagnetic Waves – Class 12 Physics

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🔹 Introduction

Electromagnetic waves are transverse waves consisting of electric field (E) and magnetic field (B) oscillating perpendicular to each other and the direction of wave propagation.

Proposed by James Clerk Maxwell.

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🔹 Displacement Current

Maxwell added the concept of displacement current to Ampere’s law.

I_d = \varepsilon_0 \frac{d\Phi_E}{dt}

Where:

 = Displacement current

 = Permittivity of free space

 = Rate of change of electric flux

📌 Diagram: Parallel plate capacitor showing conduction and displacement current

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🔹 Maxwell’s Equations (Conceptually)

1. Gauss’s law for electricity

2. Gauss’s law for magnetism

3. Faraday’s law of induction

4. Ampere-Maxwell law

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🔹 Nature of Electromagnetic Waves

Electric and Magnetic fields oscillate perpendicular to each other and to the direction of propagation.

They do not require any medium to travel.

Speed of EM Waves (in vacuum):

c = \frac{1}{\sqrt{\mu_0 \varepsilon_0}} \approx 3 \times 10^8 \text{ m/s}

📌 Diagram: EM wave with E and B fields perpendicular to each other and to direction of motion

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🔹 Electromagnetic Spectrum

Region Wavelength Range Application Example

Radio waves > 0.1 m Communication (TV, FM, etc.)

Microwaves 1 mm – 30 cm Cooking (microwave ovens), radar

Infrared 700 nm – 1 mm Remote controls, night vision

Visible 400 – 700 nm Human vision

Ultraviolet 10 nm – 400 nm Sterilization, vitamin D

X-rays 0.01 – 10 nm Medical imaging

Gamma rays < 0.01 nm Cancer treatment, nuclear reactions

📌 Diagram: Full electromagnetic spectrum (radio to gamma rays)

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🔹 Characteristics of EM Waves

They are transverse waves.

Carry energy and momentum.

Follow principle of superposition.

Can be polarized.

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🔹 Uses of EM Waves

Radio waves – Broadcasting

Microwaves – Cooking, satellites

Infrared – Remote sensors, heaters

Visible light – Vision, photography

Ultraviolet – Sterilization

X-rays – Imaging

Gamma rays – Radiotherapy

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🔹 Key Formulas

Speed of light:

c = \lambda \nu

u = \varepsilon_0 E^2

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🖼️ Important Diagrams to Include:

1. Displacement current in capacitor

2. Orientation of E, B, and propagation direction in EM waves

3. Electromagnetic spectrum chart with uses

4. Comparison of wavelengths and frequencies

5. Re

al-life applications (X-ray, microwave oven, radio antenna)

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✍️ Written by: Shahid – Study with Shahid

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