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

a convex lens of power 3.5D is placed in contact with a concave lens of power -1.5D. Find the effective focal length of the combination.

A convex lens of focal length 40cm is in contact with a concave lens of focal length 25cm. The power of the combination is

A convex lens of focal length 84 cm is in contact with a concave lens of focal length 12 cm . The power of combination (in diopters) is

A convex lens of power 3 D is held in contact with a concave lens of power -1D.A parallel beam of light is made to fall on the combination. At what distance from the combination will the beam get focussed?