Question

A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in diopters of the combination is :

• A. 25
• B. 50
• C. infinite
• D. zero

Answer 1

Answer: (D)

zero

Answer 2

PC = P1+P2P1 $\rightarrow$ Power of convex Lens P2 =100f (in cm) =10025
=+4DP2 $\rightarrow$ Power of concave lens P2=100−25 =−4DPC = P1+P2 = 4−4 = 0

Therefore, the correct option is (D): zero