7.15 x 10^17 photons strike the leaf every second if solar radiation is 1190 w/m2 strike .
Solar radiation intensity = 1200 W/m2
= 1200 J/m2 s-1 (1 W = 1 J/s)
Area of leaf = 2.35 cm2
= 2.35 x 10-4 m2 (1 cm2 = 10-4 m2)
Total energy striking leaf per second = intensity x area x time
= 1200 J/m2 s-1 x 2.35 x 10-4 m2 x 1 s
= 0.282 J
Wavelength λ = 504 nm = 504 x 10-9 m (1 nm = 10-9 m)
Energy of 1 photon E = hc/λ
= 6.626 x 10-34 x 2.998 x 108/504 x 10-9
= 3.9414 x 10-19 J
where h is Planck constant and c is speed of light
Number of photons striking leaf per second = total energy/energy of 1 photon
= 0.282/3.9414 x 10-19
= 7.15 x 10^17 photons
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