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NCERT Class XII Chapter
Dual Nature of Radiation and Matter
Questions With Solutions

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Question : 5
Total: 37
The energy flux of sunlight reaching the surface of the earth is 1.388 × 103 W m–2. 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.
Solution:  
Energy of each photon, E =
hc
λ
 =
6.63×10−34×3×108
550×10−9
= 3.62 × 10−19 J
Number of photons incident on earth’s surface per second per square metre total energy per square metre
=
total‌energy‌per‌square‌metre‌per‌second‌reaching‌on‌earth‌surface
energy‌of‌each‌photon

=
1.388×103
3.62×10−19
 = 3.8 × 1021
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