Answer the following questions :
If two lenses of focal length 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 power of these lenses, state the formula for the power of the combination .

If two convex lenses of focal lengths 10 cm and 5 cm are kept in contact with each other , What is their combined focal length ?

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

Fill in the blanks : If two lenses with focal lengths 10cm and 20 cm respectively are kept in contact with each other , the effective power of the combination is ………….

Two thin lenses of focal lengths f_(1) and f_(2) are in contact. The focal length of this combination is

If a convex lens of focal length 20 cm and a concave lens of focal length 30 cm are kept in contact with each other . (i) What will be the focal length of the combination ? (ii) What will be the power of the combination ? (iii) What will be the behaviour of the combination ?

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

Give the formula for calculating the power of combination of two lenses.