The rms value of the electric field of the light coming from the Sun is 720 N/C. The average total energy density of the electromagnetic wave is (a) 4.58 × 10⁻⁶ J/m³ (b) 6.37 × 10⁻⁹ J/m³ (c) 81.35 × 10⁻¹² J/m³ (d) 3.3 × 10⁻³ J/m³

Answer: (a). Average total energy density u = ε₀ Erms² (half electric, half magnetic). u = 8.85 × 10⁻¹² × 720² = 8.85 × 10⁻¹² × 5.18 × 10⁵ u ≈ 4.58 × 10⁻⁶ J/m ³ So the answer is (a) 4.58 × 10⁻⁶ J/m ³.

The rms value of the electric field of the light coming from the Sun… | JEE Main 2006 (AIEEE)

Q36JEE Main 2006 · AIEEEEasy

Energy Density & Intensity

The $rms$ value of the electric field of the light coming from the Sun is $720\text{ N/C}.$ The average total energy density of the electromagnetic wave is

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Answer: (a)

Average total energy density $u = \varepsilon_0 E_{rms}^2$ (half electric, half magnetic).
$u = 8.85 \times 10^{-12} \times 720^2 = 8.85 \times 10^{-12} \times 5.18 \times 10^{5}$
$u \approx 4.58 \times 10^{-6}$ J/m $^3$
So the answer is (a) $4.58 \times 10^{-6}$ J/m $^3$ .

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