Assuming the sun is directly overhead, the surface of the earth receives sunlight at 1.4 imes 10^3 W m ⁻² . Treat the light as monochromatic with an average wavelength of 500 nm , and assume no light is absorbed between the sun and the eart

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Assuming the sun is directly overhead, the surface of the earth receives sunlight at 1.4 imes 10^3 W m ⁻² . Treat the light as monochromatic with an average wavelength of 500 nm , and assume no light is absorbed between the sun and the earth's surface. The distance from the sun to the earth is 1.5 10¹¹ m . Determine the number of photons falling per second on each square metre of the earth's surface directly below th

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Correct answer: A. 3.5 10²¹

Intensity of sunlight on the earth's surface, I = 1.4 10^3 W m ⁻² Energy of a single photon is given by E = hc Substituting the given values: E = 6.63 10⁻³⁴ 3 10^8 500 10⁻⁹ = 3.98 10⁻¹⁹ J The number of photons falling per second per square metre is n = I E n = 1.4 10^3 3.98 10⁻¹⁹ 3.5 10²¹

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