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Lens Maker's Formula

Will the foca...

Question

Will the focal length of a lens for red light be more, same or less than that for blue light ?

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Solution

By len`s maker formula
$\frac{1}{f} = (\frac{μ_{1}}{μ_{2}} - 1) (\frac{1}{r_{1}} - \frac{1}{r_{2}})$
The refactive index of red light is less then refractive index of blue light .
$μ_{r} < μ_{b}$
Hence $\frac{1}{f_{r}} < \frac{1}{f_{b}}$
Therefore , $f_{r} > f_{b}$

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