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NEET PHYSICSELECTROMAGNETIC WAVESEasy

Question

The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is: (cc = speed of electromagnetic waves)

A

1 : 1

B

1 : c

C

1 : c²

D

c : 1

Step-by-Step Solution

  1. Energy Density: The intensity of an electromagnetic wave is the energy transported per unit area per unit time. This energy is stored in the electric and magnetic fields of the wave.
  2. Equipartition of Energy: In a plane electromagnetic wave traveling in a vacuum, the average electric energy density (uE⟨u_E⟩) and the average magnetic energy density (uB⟨u_B⟩) are equal. uE=14ϵ0E02⟨u_E⟩ = \frac{1}{4}\epsilon_0 E_0^2 uB=14μ0B02⟨u_B⟩ = \frac{1}{4\mu_0} B_0^2
  3. Proof: Using the relation E0=cB0E_0 = cB_0 and c=1/μ0ϵ0c = 1/\sqrt{\mu_0\epsilon_0}, we can substitute into the expression for uE⟨u_E⟩: uE=14ϵ0(cB0)2=14ϵ0(1μ0ϵ0)B02=14μ0B02=uB⟨u_E⟩ = \frac{1}{4}\epsilon_0 (cB_0)^2 = \frac{1}{4}\epsilon_0 (\frac{1}{\mu_0\epsilon_0}) B_0^2 = \frac{1}{4\mu_0} B_0^2 = ⟨u_B⟩.
  4. Conclusion: Since the energy densities are equal, the electric and magnetic fields contribute equally to the total energy and thus to the intensity of the wave. The ratio is 1:1.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from ELECTROMAGNETIC WAVES. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSELECTROMAGNETIC WAVEScontributionselectricmagneticcomponentsintensity

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