Question

When a monochromatic light isusedinsteead of blue light in a convex lens

Answer 1

Focal length is inversely proportion to n

f=1/n-1

where n is refractive index

we know that red light has less refractive index then blue colour

so focal length of convex lens will increase when red light is used instead of blue light

Answer 2

Answer:

Refractive index of red light is less than the refractive index of blue light. So, the focal length of the lens will increase when red light is used.