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NCERT Class XI Chemistry Structure of Atom Solutions

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Question : 8 of 67
Marks: +1, -0
What is the number of photons of light with a wavelength of 4000 pm that provide 1 J of energy?
Solution:  
Wavelength of light (λ) = 4000 pm
= 4000 × 10−1210^{-12} m = 4 × 10−910^{-9} m [Since 1 pm = 10−1210^{-12} m]
E = hu = h × cλ\frac{c}{\lambda} = 6.626×10−34×3×1084×10−9\frac{6.626 \times 10^{-34} \times 3 \times 10^8}{4 \times 10^{-9}} = 4.97 × 10−17 J10^{-17}\,\text{J}
Number of photons providing 1 J of energy = 14.97×10−17\frac{1}{4.97 \times 10^{-17}} = 2.012 × 101610^{16} photons.
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