The power of a convex lens is 2.5 dioptres. Find its focal length. (O

1.	The power of a convex lens is 2.5 dioptres. Find its focal length. (OR) Calculate the focal length of a corrective lens having power +2.5 D.
Answer» Data: Convex lens, P = +2.5 D, f = ? P = \(\frac{1}{f}\) ∴ 2.5 D = \(\frac{1}{f}\) ∴ f = \(\frac{1}{2.5D}\) = 0.4 cm = 40 cm The focal length of the lens = 40 cm.

The power of a convex lens is 2.5 dioptres. Find its focal length. (OR) Calculate the focal length of a corrective lens having power +2.5 D.

Answer»

Data: Convex lens, P = +2.5 D, f = ?

P = \(\frac{1}{f}\)

∴ 2.5 D = \(\frac{1}{f}\)

∴ f = \(\frac{1}{2.5D}\) = 0.4 cm = 40 cm

The focal length of the lens = 40 cm.