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NEET Sample Paper NEET Sample Test Paper-18

  • question_answer
    A convex lens of focal length f is placed somewhere in between an object and a screen so that an image is formed on the screen. The distance between the object and the screen is\[x.\]If the magnitude of magnification produced by the lens is m, the focal length of the lens is:

    A) \[\frac{mx}{{{(m+1)}^{2}}}\]                  

    B) \[\frac{mx}{{{(m-1)}^{2}}}\]

    C)  \[\frac{{{(m+1)}^{2}}x}{m}\]                 

    D) \[\frac{{{(m-1)}^{2}}x}{m}\]  

    Correct Answer: A

    Solution :

    \[-m=-\frac{v}{u}\Rightarrow v=mu\] According to problem,\[u+v=x.u=\frac{x}{1+m},\] \[v=\frac{mx}{1+m}\] By the formula \[\frac{1}{f}=\frac{1}{u}+\frac{1}{v},f=\frac{mx}{{{(m+1)}^{2}}}\] Hence, the correction option is [a].


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