Two convex lenses have focal lengths of 50 cm and 25 cm, respectively. If these two lenses are placed in contact, then the net power of this combination will be equal to
+2 dioptre
+6 dioptre
-6 dioptre
+3 dioptre
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC NDA-2 – 2022
Given focal lengths: f1 = 50 cm = 0.5 m and f2 = 25 cm = 0.25 m. Both are convex lenses, so focal lengths are positive.
Power of the first lens: P1 = 1 / f1 = 1 / 0.5 m = +2 Dioptre (D).
Power of the second lens: P2 = 1 / f2 = 1 / 0.25 m = +4 Dioptre (D).
Net power of the combination: P_net = P1 + P2 = +2 D + +4 D = +6 D.