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

Obtain an expression for focal length of a combination of thin lenses in contact.

When two thin lenses are kept in contanct, the focal length of the combination is

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.

If two lenses of focal lengths f_(1) and f_(2) are kept in contact with each other, state the formula for the focal length of the combination . If P_(1) and P_(2) are the powers of these lenses, state the formula for the power of the combination.

Derive the relation : (1)/(F) =(1)/(f_(1)) +(1)/(f_(2)) ,where f_(1) and f_(2) are focal length of two thin lenses and F is the focal length of the combination in contact.

The focal length of the combination of two thin lenses in contact is 80 cm. If the focal length of one lens is -20 cm, what is the power of the other lens ?

A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in close contact with one another. a) What is the power of this combination? b) What is the focal length of this combination? c) Is the combinatioin converging or diverging?

" two thin lenses of equal focal length but of opposite nature are pair in contact,the resultant focal length of the combination will be "