The ratio of powers of a thin convex and thin concave lens is 3/2 and equivalent focal length of their combination is 30 cm. Then their focal lengths respectively are

A comvex lens and a concave lens are placed in contact. The ratio of magnitude of the power of the convex lens to that of the concave lens is 4:3. If the focal length of the convex lens is 12 cm, then the focal length of the combination will be

A comvex lens and a concave lens are placed in contact. The ratio of magnitude of the power of the convex lens to that of the concave lens is 4:3. If the focal length of the convex lens is 12 cm, then the focal length of the combination will be

A thin convex lens is put in contact with a thin concave lens of equal focal length. The effective power and focal length of the lens combination respectively are

When a thin convex lens is put in contact with a thin concave lens of the same focal length (f), then the resultant combination has focal length equal to

When a thin convex lens is put in contact with a thin concave lens of the same focal length (f), then the resultant combination has focal length equal to

A convex lens of focal length f is put in contact with a concave lens of the same focal length. The equivalent focal length of the combination is :

A convex lens of power +2.5 D is in contact with a concave lens of focal length 25 cm. The power of combination is