The Total solution for NCERT class 6-12
Whatis the focal length of a convex lens of focal length 30 cm in contact with aconcave lens of focal length 20 cm? Is the system a converging or a diverginglens? Ignore thickness of the lenses.
Focal length of the convex lens, f1 = 30 cm
Focal length of the concave lens, f2 = −20 cm
Focal length of the system of lenses = f
The equivalent focallength of a system of two lenses in contact is given as:
Hence,the focal length of the combination of lenses is 60 cm. The negative signindicates that the system of lenses acts as a diverging lens.