Optics Question 631
Question: An object is placed first at infinity and then at 20 cm from the object side focal plane of the convex lens. The two images thus formed are 5 cm apart. The focal length of the lens is
[SCRA 1994]
Options:
A) 5 cm
B) 10 cm
C) 15 cm
D) 20 cm
Show Answer
Answer:
Correct Answer: B
Solution:
For first case :
For second case
Alternative sol.:
Therefore
