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Question

The focal length of quartz lens for yellow color is 15.5 cm for which refractive index of quartz is 1.504. Find the focal length of same lens (in cm) for ultraviolet color for which refractive index is 1.434.

Moderate

Solution

$\begin{matrix} \frac{1}{15 .5} = (1 .504 - 1) (\frac{1}{R_{1}} - \frac{1}{R_{2}}) \\ \frac{1}{f} = (1 .434 - 1) (\frac{1}{R_{1}} - \frac{1}{R_{2}}) \\ \frac{f}{15 .5} = \frac{0 .504}{0 .434} \\ f = 15 .5 \times \frac{252}{217} = 18 cm \end{matrix}$

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Similar Questions

A thin convex lens is made of two materials with refractive indices $n_{1}$ and $n_{2}$ , as shown in figure. The radius of curvature of the left and right spherical surface are equal. $f$ is the focal length of the lens when $n_{1} = n_{2} = n$ . The focal length is $f + Δ f$ when $n_{1} = n$ and $n_{2} = n + Δ n$ . Assuming $Δ n < < (n - 1)$ and $1 < n < 2$ , the correct statement(s) is/are,