Question

how does the focal lenght of lens change when red light incident on it is replaced by violet light?

Answer 1

Hi friend,

For a spherical mirror the focal length remains unaffected with all three parameters; wavelength, refractive index and frequency.

The focal length of the lens varies directly with the wavelength of the light used and as wavelength is inversely related to refractive index, the focal length also varies inversely with it. This is the principal cause of the phenomena of chromatic aberration. The frequency of light has no effect on the focal length.

So, focal length in creases with wavelength but decreases with refractive index and vice versa.

Hope this helps you....
Please mark it as brainliest answer...

Answer 2

focal length depend upon refractive index of the medium .
e.g
1/f = (u - 1) { 1/R1 - 1/R2}
hence, focal length inversely proportional to refractive index of the medium .
we also know , refractive index = velocity of light in vaccum /velocity of light in medium .

but we know velocity of red light greater then then velocity of violet light .
hence refratice index increase from red to Violet .
hence focal length decrease from red to violet .