Question

how the focal length of a lens change with increase in the wavelength of the light?Explain and make it simple to understand.

Answer 1

Focal length varies directly with wavelength  and as wavelength is inversely with refractive index, its also varies inversely with the wavelength .

Focal length increases with wavelength and decreases with refractive index .
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As we all know that Cuachy's equation gives relationship between refractive
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index and wavelength of light for a particular transparent material and again
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lens formula gives a relationship between focal length and refractive index, so
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eliminating refractive index term from both equation should give you a
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mathematical relation between the wavelength and the focal distance.
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n(λ) = B + C/λ²

Here B and C are coefficient determined for the material .

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Hope it helps :]
 

Answer 2

Dear Student,

◆ Answer -

Focal length is increases with increase in wavelength of light passed.

● Explanation -

Focal length is directly proportional to wavelength of light passed. As red light has higher wavelength, it refracts less and has greater focal lens. On the contrary, blue light converges more and has small focal length.

Thanks dear. Hope this helps you..