Physics

Class 12

Physics · Class 12 · Chapter 8

Electromagnetic Waves

11 lessons 84 min 2 simulations

A changing magnetic field makes an electric field; this chapter adds the reverse, that a changing electric field makes a magnetic field. Maxwell's displacement current repairs Ampere's law for a charging capacitor, completes the four Maxwell equations and predicts waves of coupled E and B fields that travel at the speed of light. The chapter then describes these waves and walks through the whole electromagnetic spectrum, from radio waves to gamma rays.

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What the exam asks

NEET asks for the displacement current ε₀ dΦE/dt, the relation B₀ = E₀/c, c = 1/√(μ₀ε₀), reading λ and ν from a wave equation, the direction of E, B and travel, and above all the order of the spectrum with the source, detector and use of each band. Marks are lost by mixing up the order (UV and X-ray, IR and microwave), by thinking B₀ equals E₀, and by forgetting that every em wave has the same speed in vacuum.

Lessons

11 lessons · 84 min