Dispersion of light#!#Application of Convex lens

What is a convex lens ?

Optical centre of convex lens:

As source of light is at the focus of convex lens. The outcoming light through the lens will be in the form of

An achromatic lens -double is formed by in contact a convex lens of focal length 20 cm amd a concave lens of focal length 30 cm.The dispersive of the meterial of the convex lens is 0.18 (a) Determine the dispersive power of the meterial of the concave lens (b) Calculate the focal of the lens-doublet 0.27 (b) 60 cm

When monochromatic red light is used instead of blue light in a convex lens, its focal length will :-

Principal focus of convex lens:

If the behavior of light rays through a convex lens is as shown in the adjoining figure, then

Which of the two diverges a beam of parallel rays of light : convex lens or concave lens ?