question_answer 10)

What is the focal length of a convex lens of focallength 30 cm in contact with a concave lens offocal length 20 cm ? Is the system a converging ora diverging lens ? Ignore thickness of the lenses. 

Answer:

Here,and For the combination of two thin lenses, thefocal length of the combination is given by Since the focal length is negative, thecombination is a diverging lens.