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The rms electric field associated with sunlight is 720 N/C. What is the mean total energy density of this electromagnetic wave?

1. 4.58 × 10⁻⁶ J/m³
2. 6.37 × 10⁻⁹ J/m³
3. 81.35 × 10⁻¹² J/m³
4. 3.3 × 10⁻³ J/m³

Correct answer: 4.58 × 10⁻⁶ J/m³

Solution

u = epsilon0 * E_rms^2 = (8.85e-12)(720)^2 = 8.85e-12 * 5.184e5 = 4.58e-6 J/m^3.

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