A convex lens is placed in contact with a mirrorr as shown. If he space between them is filed with water, its power will

Two equi convex lenses each of focal lengths 20 cm and refractive index 1.5 are placed in & contact and space between them is filled with water of refractive index 4/3 . The combination works as

A convex lens is placed in contact with a plane mirror. An axial point object at a distance of 20 cm from this combination, has its image coinciding with itself. What is the focal length of the convex lens ?

A convex lens is placed in contact with a plane mirror. An axial point object at a distance of 20 cm from this combination, has its image coinciding with itself. What is the focal length of the convex lens ?

A convex lens of power +5 D is placed in contact with a concave lens of power -4 D. What is the power of combination and nature of lens combination ?

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

A convex lens of power 4D is kept in contact with a concave lens of power 3D, the effective power of combination will be

A convex lens of power 4D is kept in contact with a concave lens of power 3D, the effective power of 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