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Stopping Potential Revisited

The energy fl...

Question

The energy flux of sunlight reaching the surface of the earth is 1.388 × 10³ W/m². How many photons (nearly) per square metre are incident on the Earth per second? Assume that the photons in the sunlight have an average wavelength of 550 nm.

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Solution

Energy flux of sunlight reaching the surface of earth, Φ = 1.388 × 10³ W/m²

Hence, power of sunlight per square metre, P = 1.388 × 10³ W

Speed of light, c = 3 × 10⁸ m/s

Planck’s constant, h = 6.626 × 10⁻³⁴ Js

Average wavelength of photons present in sunlight,

Number of photons per square metre incident on earth per second = n

Hence, the equation for power can be written as:

Therefore, every second, photons are incident per square metre on earth.

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