Question

The radius of curvature of the convex face of a planoconvex lens is $15cm$ 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
• E. 1.4

Answer 1

Answer: (D)

$\frac{1}{f}(\mu -1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$
For planoconvex lens $R_1=\infty ,R_2=-R=-1.5cm,\mu =1.4$
$\therefore$ $\frac{1}{f}=(1.4-1)\left(0+\frac{1}{15}\right)$
or $\frac{1}{f}=0.4\times \frac{1}{15}$
Therefore, power of the lens in diopter
$P=\frac{100}{f}=\frac{40}{15}=2.66D$