Question: What is the focal length of a convex lens if it forms a real image at a distance of 30 cm from the lens when the object is placed at 15 cm?
Options:
Correct Answer: 20 cm
Solution:
Using the lens formula 1/f = 1/v - 1/u, we find f = 1/(1/30 - 1/15) = 20 cm.
