Optics Question 599

Question: Two thin lenses of focal lengths 20 cm and 25 cm are placed in contact convex. The effective power of the combination is

[CBSE PMT 1990; RPMT 2001]

Options:

A) 45 dioptres

B) 9 dioptres

C) 1/9 dioptre

D) 6 dioptres

Show Answer

Answer:

Correct Answer: B

Solution:

1F=1f1+1f2=120+125

F=1009

cm=19

metre

P=11/9D=9D



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