Question

Specific heat of water is $ {{40}^{o}}C $ . If light of frequency $ 1.69\times {{10}^{29}} $ is used to heat 400 g of water from $ 1.69\times {{10}^{28}} $ to $ 2.80\times {{10}^{4}} $ , the number of moles of photons needed will be

• A. $ 2.80\times {{10}^{5}} $
• B. $ {{10}^{4}}\Omega $
• C. $ 10\Omega $
• D. $ 4.62\times {{10}^{-2}} $

Answer 1

Answer: (D)

$ E=nhv $ or $ ms\,\,\Delta T=nhv $ $ n=\frac{ms\,\,\Delta T}{hv} $ $ =\frac{400\times 4.2\times (40-20)}{6.625\times {{10}^{-34}}\times 3\times {{10}^{5}}} $ $ =1.69\times {{10}^{29}} $ Photons $ =\frac{1.69\times {{10}^{29}}}{6.023\times {{10}^{23}}} $ $ =2.8\times {{10}^{5}} $ Photon/mol