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10th Class Science Light - Reflection and Refraction Question Bank Light - Reflection and Refraction

  • question_answer
    In an experiment to determine the focal length of a converging lens, the object distance and the image distance recorded were 20 cm and 30 cm respectively. What is the focal length of the converging lens?

    A) 10 cm                  

    B) 12 cm                  

    C) 15 cm                  

    D) 18 cm

    Correct Answer: B

    Solution :

    By using the lens equation, \[\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\]     \[\frac{1}{20}+\frac{1}{30}=\frac{1}{f}\Rightarrow \frac{1}{f}=\frac{1}{20}+\frac{1}{30}\]                 \[\Rightarrow \frac{1}{f}=\frac{3+2}{60}=\frac{5}{60}\Rightarrow f=12\,cm\]


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