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Electromagnetic Waves appeared 31 times across 3 years — 3.6% of Physics. This question is from Properties of EM Waves.

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Questions 10 12 9 31
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Given below are two statements: Statement I: Electromagnetic waves carry energy as they travel through space and this energy is equally shared by the electric and magnetic fields. Statement II: When electromagnetic waves strike a surface, a pressure is exerted on the surface. In the light of the above statements, choose the most appropriate answer from the options given below:

Solution & Explanation

Related Formula
ρE = (1)/(2)ε₀ Erms² ρB = Brms²2μ₀

pᵣ = (I)/(c) (radiation pressure for completely absorbing surface)

Core Logic

Statement I: In an EM wave, energy is stored in both the electric and magnetic fields. The energy densities are equal: UE = UB because E = cB and c² = (1)/(μ₀ ε₀). This is a correct fact.

Statement II: Electromagnetic waves carry momentum (p = U/c). When they strike a surface, they transfer this momentum, creating radiation pressure. This is also a correct fact.

Step 1: Final Evaluation

Since both facts are universally true theoretical properties of EM waves, both statements are correct.

Pattern Recognition

Standard NCERT theory. Energy density is strictly symmetric 50-50 between E and B. Momentum transfer → pressure is the definitive signature of the particle-like nature (photons) of EM waves.

Chapter Mix

Class 12 Physics: Electromagnetic Waves

Reference Study Guides

Electromagnetic Waves

More Electromagnetic Waves Previous-Year Questions — Page 7

Q40 jee_main_2024_31_jan_morning Energy Density Of EM Waves
In a plane EM wave, the electric field oscillates sinusoidally at a frequency of 5 × 10¹⁰ ~Hz and an amplitude of 50 ~Vm⁻¹. The total average energy density of the electromagnetic field of the wave is : [Use ε₀ = 8.85 × 10⁻¹² C² / Nm² ]
  • A. 1.106 × 10⁻⁸ Jm⁻³
  • B. 4.425 × 10⁻⁸ ~Jm⁻³
  • C. 2.212 × 10⁻⁸ ~Jm⁻³
  • D. 2.212 × 10⁻¹⁰ ~Jm⁻³

Solution

Related Formula
Utotal average = (1)/(2)ε₀ E₀²
Core Logic

For an electromagnetic wave, the total average energy density is the sum of the average energy density of the electric field and the magnetic field. They are equal, so:

Uavg = UE + UB = 2UE = 2 ( (1)/(4)ε₀ E₀² ) = (1)/(2)ε₀ E₀²

Where E₀ is the amplitude of the electric field.

Step 2: Substitution

Given: E₀ = 50 V/m ε₀ = 8.85 × 10⁻¹² C²/(N· m²)

Uavg = (1)/(2) × (8.85 × 10⁻¹²) × (50)² Uavg = (1)/(2) × 8.85 × 10⁻¹² × 2500 Uavg = 1.10625 × 10⁻⁸ J/m³
Chapter Mix

Class 12 Physics: Electromagnetic Waves

More Electromagnetic Waves Questions — jee_main_2024_31_jan_evening

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Rankbit System
JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%) | JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%)