The sun delivers 10^3 Wm^-2 of electromagnetic flux to the...

The sun delivers $10^{3} \mathrm{Wm}^{-2}$ of electromagnetic flux to the earth's surface. The radiation force on the roof of dimensions $10 \mathrm{~m} \times 20 \mathrm{~m}$ is (a) $6.67 \times 10^{-6} \mathrm{~N}$ (b) $6.67 \times 10^{-4} \mathrm{~N}$ (c) $6.67 \times 10^{-1} \mathrm{~N}$ (d) $2.35 \times 10^{-4} \mathrm{~N}$

The sun delivers $10^{3} \mathrm{Wm}^{-2}$ of electromagnetic flux to the earth's surface. The radiation force on the roof of dimensions $10 \mathrm{~m} \times 20 \mathrm{~m}$ is
(a) $6.67 \times 10^{-6} \mathrm{~N}$
(b) $6.67 \times 10^{-4} \mathrm{~N}$
(c) $6.67 \times 10^{-1} \mathrm{~N}$
(d) $2.35 \times 10^{-4} \mathrm{~N}$

Key Concepts

Electromagnetic Radiation Pressure

Electromagnetic radiation carries momentum as well as energy, which leads to the concept of radiation pressure—the pressure exerted upon any surface due to the momentum transfer of the photons. This pressure is directly related to the intensity of the radiation and inversely proportional to the speed of light, connecting the energy flux (power per unit area) to the force per unit area exerted on surfaces exposed to the radiation.

Intensity (Electromagnetic Flux)

Intensity, measured in watts per square meter (W/m²), quantifies the power carried by electromagnetic waves per unit area perpendicular to the direction of propagation. It is a key concept in calculating radiation pressure since it serves as the energy input that, when divided by the speed of light and adjusted for the nature of the interaction (absorption or reflection), determines the resulting force on a surface.

Momentum Transfer in Electromagnetic Waves

Momentum transfer in electromagnetic waves occurs when photons collide with or are reflected by a surface, thereby imparting momentum and causing a force. Using the relation that the momentum of a photon is proportional to its energy divided by the speed of light, one can link the energy flux of radiation to a mechanical force on a surface, allowing for calculations of radiation pressure and resultant forces on objects.

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