A convex lens and a concave lens are kept separated by a distance d. If they are placed in close contact, the focal length of the combination

A convex and a concave lens separated by distance d are then put in contact . The focal length of the combination

A convex lens of focal length x and a concave lens of focal length y are placed in contact. The focal length of the combination is

A convex lens of focal length A and a concave lens of focal length B are placed in contact. The focal length of the combination is

A convex lens of focal length A and a concave lens of focal length B are placed in contact. The focal length of the combination is

A convex lens of focal length f_1 and a concave lens of focal length f_2 are placed in contact. The focal length of the combination is f. Then

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 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 :

If a convex lens of focal length 20 cm and a concave lens of focal length 30 cm are kept in contract with each other. What will be the focal length of the combination ?