Question 247: Ray Optics

Question

Diameter of a plano-convex lens is $$6$$ $$cm$$ and thickness at the center is $$3mm$$. If speed of light in material of lens is $$2 	imes {10^8}\,m/s,$$ the focal length of the lens is

Accepted Answer

$$	herefore$$ $$n = {{Velocity\,\,of\,\,light\,\,in\,\,vacuum} \over {Velocity\,\,of\,\,light\,\,in\,\,medium}}$$
$$	herefore$$ $$n = {3 \over 2}$$
$${3^2} + {\left( {R - 3mm} ight)^2} = {R^2}$$
$$ \Rightarrow {3^2} + {R^2} - 2R\left( {3mm} ight) + {\left( {3mm} ight)^2} = {R^2}$$
$$ \Rightarrow R \approx 15\,cm$$
$${1 \over f} = \left( {{3 \over 2} - 1} ight)\left( {{1 \over {15}}} ight) \Rightarrow f = 30\,cm$$

Answer

$$15$$ $$cm$$

Answer

$$20$$ $$cm$$

Answer

$$30$$ $$cm$$

Answer

$$10$$ $$cm$$

Ray Optics

Diameter of a plano-convex lens is $6 cm and thickness at the center is 3mm. If speed of light in material of lens is 2 \times {10^8}\,m/s,$ the focal length of the lens is

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