A planoconvex lens has the radius of curvature of its curved surface 50 cm and the refractive index of its material is 1.5. Its focal length will be

1 m

The correct answer is Option (1) → 1 m

Given: Radius of curvature $R = 50\ \text{cm}$, refractive index $\mu = 1.5$

For a planoconvex lens, one surface is plane $(R_2 = \infty)$ and the other is convex $(R_1 = +R)$.

Using the lens maker’s formula:

$\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right)$

Substitute values:

$\frac{1}{f} = (1.5 - 1)\left(\frac{1}{50} - \frac{1}{\infty}\right)$

$\frac{1}{f} = 0.5 \times \frac{1}{50}$

$\frac{1}{f} = \frac{1}{100}$

∴ $f = 100\ \text{cm}$

Answer: $f = 100\ \text{cm}$