Question

When monochromatic red light is used instead of blue light in a convexlens, its focal length will

Answer 1

A convex lens is inverted like a inverted prism.

The phase velocity is different for each colour.

When the light comes out from the other side, the bending is more for red and less is for blue

. Therefore, the focal length, which is due to bending changes more as compared with the blue light

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Answer 2

Answer:

Focal length of the convex lens increases with the increase in wavelength. We know wavelength of red is more than the wavelength of violet. So, as the wavelength decreases the focal length also decreases.