Physics - Geometrical Optics Question with Solution | TestHub

Focal length of a convex lens having power $2.5\mathrm{D},=\frac{1}{2.5}\mathrm{m}$ Also focal length of a lens in a medium of refractive index $\mu$ is given by $\frac{1}{f}=(\mu -1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$
Dividing the two, $2.5\frac{0.5}{-0.25}$ $\Rightarrow \frac{1}{f^{\prime }}=\frac{-5}{25\times 0.25}=-1.25\mathrm{D}$