Three lenses in contact have a combined focal length of 12 cm. When the third lens is removed, the combined focal length is `(60)/(7)` cm. The third lens is

Two thin lenses, one of focal length + 60 cm and the other of focal length - 20 cm are put in contact, the combined focal length is,

Two thin lenses, one of focal length + 60 cm and the other of focal length – 20 cm are put in contact. The combined focal length is

Two thin lenses, one of focal length + 60 cm and the other of focal length – 20 cm are put in contact. The combined focal length is

Two thin lenses, aone convex of focal length 10 cm and other concave lens are kept in contact to form a composite lens of focal length 13 cm . If the combination acts as a converging lense the focal length of second lens is

Two thin lenses, aone convex of focal length 10 cm and other concave lens are kept in contact to form a composite lens of focal length 13 cm . If the combination acts as a converging lense the focal length of second lens is

We combined a convex lens of focal length f_(1) and concave lens of focal lengths f_(2) and their combined focal length was F . The combination of these lenses will behave like a concave lens, if

We combined a convex lens of focal length f_(1) and concave lens of focal lengths f_(2) and their combined focal length was F . The combination of these lenses will behave like a concave lens, if