A parallel beam of intensity 1500 W·m⁻² falls on a plane surface of area 0.020 m² at an angle 60° with the surface normal. The surface absorbs 40% of the intercepted radiation, specularly reflects 50%, and transmits 10% without deflection. Which pair is closest to the normal and tangential components of radiation force on the surface?
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Question

A parallel beam of intensity 1500 W·m⁻² falls on a plane surface of area 0.020 m² at an angle 60° with the surface normal. The surface absorbs 40% of the intercepted radiation, specularly reflects 50%, and transmits 10% without deflection. Which pair is closest to the normal and tangential components of radiation force on the surface?

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G1 Physics · Accepted Answer

The intercepted power on an oblique plane is P(hit) = IA cosθ. For the normal component, absorbed radiation contributes one normal momentum component and specularly reflected radiation contributes twice the normal momentum component. Therefore, F⊥ = IA cos²θ(A₁+2R₁) ÷ c. Substitute: I = 1500 W·m⁻², A = 0.020 m², cos60° = 0.5, A₁ = 0.40, R₁ = 0.50. Thus, F⊥ = 1500×0.020×0.25×(0.40+1.00) ÷ (3×10⁸) = 10.5 ÷ (3×10⁸) = 3.50×10⁻⁸ N. For specular reflection, the tangential momentum component is unchan…