Optics 7 Question 37

38. In the figure, light is incident on a thin lens as shown. The radius of curvature for both the surfaces is R. Determine the focal length of this system.

(2003,2M)

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Solution:

  1. For refraction at first surface,

μ2v1μ1=μ2μ1+R

For refraction at second surface,

μ3v2μ2v1=μ3μ2+R

Adding Eqs. (i) and (ii), we get

μ3v2=μ3μ1Rv2=μ3Rμ3μ1

Therefore, focal length of the given lens system is

μ3Rμ3μ1



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