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JEE Main & Advanced Physics Ray Optics Question Bank Photometry

  • question_answer
    Two stars situated at distances of 1 and 10 light years respectively from the earth appear to possess the same brightness. The ratio of their real brightness is [NCERT 1981]

    A)            1  : 10                                       

    B)            10  : 1

    C)            1  : 100                                    

    D)            100 : 1

    Correct Answer: C

    Solution :

                       \[I=\frac{L}{{{r}^{2}}}\]\[\Rightarrow \frac{{{L}_{1}}}{r_{1}^{2}}=\frac{{{L}_{2}}}{r_{2}^{2}}\]  (I is same)            \[\Rightarrow \frac{{{L}_{1}}}{{{L}_{2}}}=\frac{r_{1}^{2}}{r_{2}^{2}}={{\left( \frac{1}{10} \right)}^{2}}=1:100\].


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