Question Detail
Question
A candle placed 23 cm from a lens, forms an image on a screen placed 75 cm on the other end of the lens. The focal length and type of the lens should be
Correct Answer
Option A is the correct answer.
Detailed Explanation
Using the lens formula: 1/f = 1/u + 1/v. u = 23 cm, v = 75 cm. 1/f = 1/23 + 1/75 = (75 + 23) / (23 × 75) = 98 / 1725. f = 1725 / 98 = 17.6 cm. Since the image is formed on a screen, it is a real image, so the lens must be a converging (convex) lens.
Hint
Use the lens formula: 1/f = 1/u + 1/v. A positive f indicates a converging lens.