Question

The radius of curvature of the convex face of a planoconvex lens is $15 \,cm$ and the refractive index of the material is $1.4$ . Then the power of the lens in dioptre is

• A. 1.6
• B. 1.66
• C. 2.6
• D. 2.66

Answer 1

Answer: (D)

2.66

Answer 2

$\frac{1}{f}(\mu -1)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)$ For planoconvex lens ${{R}_{1}}=\infty ,{{R}_{2}}=-R=-1.5\,cm,\mu =1.4$ $\therefore$ $\frac{1}{f}=(1.4-1)\left( 0+\frac{1}{15} \right)$ or $\frac{1}{f}=0.4\times \frac{1}{15}$ Therefore, power of the lens in diopter $P=\frac{100}{f}=\frac{40}{15}=2.66D$