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The electric field in an electromagnetic wave is given by E = 56.5 sin(ω(t - x/c)) N C⁻¹. Find the intensity of the wave if it is propagating along x-axis in the free space. (Given ε₀ = 8.85 × 10⁻¹² C² N⁻¹ m⁻²

Asked in JEE Main 25th June 1st Shift 2022 · Intensity from the amplitudes

• (1) 5.65 W m⁻²
• (2) 4.24 W m⁻²
• (3) 1.9 × 10⁻⁷ W m⁻²
• (4) 56.5 W m⁻²

Step-by-step solution

Why the other options are wrong

• (1) 5.65 W m⁻² is just E₀/10 — no formula was applied
• (3) 1.9 × 10⁻⁷ W m⁻² is ε₀E₀²/… with c omitted; intensity needs the factor c
• (4) 56.5 W m⁻² is the field amplitude itself, carried over with the wrong unit

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