An achromatic convergent lens of focal length `150 cm` is made by combining flint and crown glass lenses. Calculate the focal length of both the lenses and point out which one is divergent if the ratio of the dispersive power of flint and crown glasses is `3:2.`

A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be:

Two thin converging lenses of focal length 15 cm and 30 cm are held in contact with each other. The focal length of the combination is

A convergent lens of power 8 D is combined with a divergent lens of power - 10 D . Calculate focal length of the combination.

An achromatic converging combination of focal length 60m is formed by placing a convex lens of crown glass and a concave lens of fibt glass in contact with each other. Calculate their focal lengths. If dispersive power of crown glass is 0.03 and that of flint glass is 0.05 .

Obtain the formula for combined focal length of two thin lenses in contact, taking one divergent and the other convergent.

Focal length of combination of two thin lenses is 1 m. Calculate the power of one lens if the focal length of other lens is 30 cm.

Two convex lenses of focal length 10 cm each are combined. What will be the focal length of the combined lens ?