A plano convex lens is made of material having refractive index 1.8. If the radius of curvature of the curved surface is 80 cm, then focal length of the lens is:

100 cm

For plano convex lens $\frac{1}{F} = (\mu -1)(\frac{1}{R}-\frac{1}{\infty} = \frac{\mu -1}{R} = \frac{0.8}{80}$

$\Rightarrow F = 100cm$

The correct answer is Option (1) → 100 cm