A double convex lens made of glass has both radii of curvature of magnitude $20 \mathrm{~cm}$. Incident light rays parallel to the axis of the lens will converge to a point at a distance ' $L$ ' from the common pole P. The value of L is [Refractive index of glass $=1.5$ ]

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Aicharya · Accepted Answer

Lens maker formula: $\frac{1}{\mathrm{f}}=(\mu-1)\left(\frac{1}{\mathrm{R}_1}-\frac{1}{\mathrm{R}_2}ight)$ If incidence ray has direction left to right \& $\left|R_1ight|=\left|R_2ight|=20 \mathrm{~cm}=\mathrm{R}, \mu=1.5$, then $\begin{aligned} & \frac{I}{f}=(\mu-1)\left(\frac{1}{R}-\frac{1}{(-R)}ight)=\frac{2(\mu-1)}{R} \ & =\frac{2(1.5-1)}{20 \mathrm{~cm}} \ & \Rightarrow f=20 \mathrm{~cm}\end{aligned}$

A double convex lens made of glass has both radii of curvature of magnitude $20 \mathrm{~cm}$. Incident…

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