A boy is trying to start a fire by focusing sunlight on a piece of paper using an equiconvex lens of focal length 10 cm. The diameter of the sun is 1.39 x 10⁹ m and its mean distance from the earth is 1.5 x 10¹¹ m. What is the diameter of the Sun’s image on the paper?

Options

(a) 9.2 x 10⁻⁴ m
(b) 6.5 x 10⁻⁴ m
(c) 6.5 x 10⁻⁵ m
(d) 12.4 x 10⁻⁴ m

Correct Answer:

9.2 x 10⁻⁴ m

Explanation:

We have, | v /u | = size of image / size of object
or, size of image = | v / u | x size of object
= (10⁻¹ / 1.5 x 10¹¹) x (1.39 x 10⁹)
= 0.92 x 10⁻³ m
Diameter of the sun’s image = 9.2 x 10⁻⁴ m