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 ?

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 .

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

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 ?

Two similar thin equiconvex lenses, of focal length f each, are kept coaxially in contact with each other such that the focal length of the combination is F_1 . When the space between the two lenses is filled with glycerin (which has the same refractive index (mu = 1.5) as that of glass) then the equivalent focal length is f_2 . The ratio F_1 : F_2 will be:

If a concave lens of focal length 12 cm and a convex lens of focal length 20 cm are kept in contact with each other . (i) Find be the focal length of the combination ? (ii) What will be the behaviour of the combination ?

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 ………….

What do you mean by combined focal length?