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Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2004

  • question_answer
    A convex lens has a focal length\[f.\] It is cut into two parts along the dotted line as shown in the figure. The focal length of each part will be

    A)  \[f\text{/2}\]                                   

    B)  \[f\]

    C)  \[\text{3/2}f\]                                 

    D)  \[2f\]

    Correct Answer: D

    Solution :

    Let focal length of the lens is f, then \[\frac{1}{f}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}\] putting \[{{f}_{1}}={{f}_{2}}=f'\] \[\therefore \]    \[\frac{1}{f}=\frac{1}{f'}+\frac{1}{f'}\](focal length of each part) \[\Rightarrow \]               \[f'=2f\]


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