NEET Physics Photo Electric Effect, X- Rays & Matter Waves NEET PYQ-Photo Electric Effect,X-Rays

  • question_answer
    A 200 W sodium street lamp emits yellow light of wavelength 0.6 um. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is                      [AIPMT (S) 2012]

    A)  \[1.5\times {{10}^{20}}\]        

    B)       \[6\times {{10}^{18}}\]

    C)  \[62\times {{10}^{20}}\]         

    D)  \[3\times {{10}^{19}}\]

    Correct Answer: A

    Solution :

    Efficient power \[p=\frac{N}{\tau }\times \frac{hc}{\lambda }=200\times 0.25\]
    \[\frac{N}{\tau }=50\times \frac{\lambda }{hc}=1.5\times {{10}^{20}}\]
    \[=\frac{50\times 0.6\times {{10}^{-6}}}{6.6\times {{10}^{-34}}\times 3\times {{10}^{8}}}\]


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