question_answer

Diameter of a plano - convex lens is 6 cm and thickness at the centre is 3 mm. If speed of light in material of lens is\[2\times {{10}^{8}}m/s,\] the focal length of the lens is:      [JEE MAIN 2013]

A) 15 cm

B) 20 cm

C) 30 cm

D) 10 cm

Correct Answer: C

Solution :

[c]

(approx.)