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Average force exerted on a non-reflecting surface at normal incidence is 2.4 × 10⁻⁴ N. If 360 W/cm² is the light energy flux during span of 1 hour 30 minutes, then the area of the surface is

Asked in JEE Main 8th April 1st Shift 2024 · Force and radiation pressure

• (1) 20 m²
• (2) 0.1 m²
• (3) 0.02 m²
• (4) 0.2 m²

Step-by-step solution

Why the other options are wrong

• (1) 20 m² needs I = 3.6 × 10³ W m⁻² — three powers of ten lost in the same conversion
• (2) 0.1 m² needs I = 7.2 × 10⁵ W m⁻² 360 W cm⁻² is 3.6 × 10⁶ W m⁻²
• (4) 0.2 m² comes from writing 360 W cm⁻² as 3.6 × 10⁵ W m⁻² — one power of ten short in the cm^-2 → m⁻² conversion (1 cm⁻² = 10⁴ m⁻²

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