If mu_0 and varepsilon_0 are the permeability and permittivity of free space, respectively, then the dimension of left(frac1mu_0varepsilon_0right) is:

Solution & Explanation

### Related Formula Maxwell's relation for the speed of light (c) in vacuum: c = frac1sqrtmu_0 varepsilon_0 ### Core Logic Square both sides of the speed of light formula: c^2 = frac1mu_0 varepsilon_0 Since c represents the speed of light (velocity), its dimensional formula is: [c] = [L T^-1] Therefore, the dimensions of c^2 are: [c^2] = [L T^-1]^2 = [L^2 T^-2] ### Step 1: Match options Express the dimensions in terms of the given variable ratios: [c^2] = fracL^2T^2 This perfectly matches Option (2). ### Pattern Recognition Sees: Dimensions of vacuum permittivity-permeability inverse product. Trap: Trying to find the separate dimensions of both mu_0 and varepsilon_0, then conducting manual division. This is extremely slow and prone to algebraic error. Shortcut: Directly identify the term as c^2. The velocity squared has units of mathrmm^2mathrms^-2, giving dimensions of mathrmL^2mathrmT^-2 immediately. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Physics: Electromagnetic Waves Class 11 Physics: Units and Measurements

Reference Study Guides

More Electromagnetic Waves Previous-Year Questions — Page 5

Q40 jee_main_2024_31_jan_evening Properties of EM Waves
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:
  • A. Statement I is incorrect but Statement II is correct
  • B. Both Statement I and Statement II are correct
  • C. Both Statement I and Statement II are incorrect
  • D. Statement I is correct but Statement II is incorrect

Solution

### Related Formula rho_E = frac12varepsilon_0 E_rms^2 rho_B = fracB_rms^22mu_0 p_r = fracIc (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: U_E = U_B because E = cB and c^2 = frac1mu_0 epsilon_0. 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 to pressure is the definitive signature of the particle-like nature (photons) of EM waves. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Physics: Electromagnetic Waves
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 times 10^10 mathrm~Hz and an amplitude of 50 mathrm~Vm^-1. The total average energy density of the electromagnetic field of the wave is : [Use varepsilon_0 = 8.85 times 10^-12 \, textC^2 / textNm^2 ]
  • A. 1.106 times 10^-8 \, mathrmJm^-3
  • B. 4.425 times 10^-8 mathrm~Jm^-3
  • C. 2.212 times 10^-8 mathrm~Jm^-3
  • D. 2.212 times 10^-10 mathrm~Jm^-3

Solution

### Related Formula U_texttotal average = frac12epsilon_0 E_0^2 ### 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: U_textavg = U_E + U_B = 2U_E = 2 left( frac14epsilon_0 E_0^2 right) = frac12epsilon_0 E_0^2 Where E_0 is the amplitude of the electric field. ### Step 2: Substitution Given: E_0 = 50 mathrm\, V/m epsilon_0 = 8.85 times 10^-12 mathrm\, C^2/(Ncdot m^2) U_textavg = frac12 times (8.85 times 10^-12) times (50)^2 U_textavg = frac12 times 8.85 times 10^-12 times 2500 U_textavg = 1.10625 times 10^-8 mathrm\, J/m^3 ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Physics: Electromagnetic Waves

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