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:
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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:

G1 Physics · Accepted Answer

For complete absorption, radiation pressure is: P = I/c Also: P = F/A Therefore: F/A = I/c A = Fc/I Given: F = 2.4 × 10⁻⁴ N I = 360 W/cm² = 360 × 10⁴ W/m² c = 3 × 10⁸ m/s Therefore: A = [2.4 × 10⁻⁴ × 3 × 10⁸]/[360 × 10⁴] = 2 × 10⁻² m² = 0.02 m²