Approximating the eye as a single thin lens 2.70 cmcm from the retina, find the focal length of the eye when it is focused on an object at a distance of 265 cmcm


  1. Answer:

    0.37 cm


    The image is formed on the retina which is at a constant distance of 2.70 cm to the lens. Therefore, image distance = 2.70 cm.

    The object is at a distant of 265 cm to the lens of the eye.

    From lens formula,

    \frac{1}{f} = \frac{1}{u} + \frac{1}{v}

    where: f is the focal length, u is the object distance and v is the image distance.

    Thus, u = 265.00 cm and v = 2.70 cm.

    \frac{1}{f} = \frac{1}{265} + \frac{27}{10}

      = \frac{10+7155}{2650}

    \frac{1}{f}  = \frac{7165}{2650}

    ⇒ f = \frac{2650}{7165}

          = 0.37

    The focal length of the eye is 0.37 cm.

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