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In the figure, light is incident on a th...

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.

Text Solution

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For refraction at first surface,
`mu_2/v_1-mu_1/-oo=(mu_2-mu_1)/(+R)`………(i)
For refraction at second surface,
`mu_3/v_2-mu_2/v_1=(mu_3-mu_2)/(+R)` …………(ii)
Adding Eqs. (i) and (ii), we get `mu_3/v_2-(mu_2-mu_1)/R or v_2=(mu_3R)/(mu_3-mu_1)`

Therefore, focal length of the given lens system is
`f=(mu_3R)/(mu_3-mu_1)`
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Knowledge Check

  • What is the refractive index of material of a plano-convex lens , if the radius of curvature of the convex surface is 10 cm and focal length of the lens is 30 cm ?

    A
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    B
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