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The graph between \mathrm{\frac{1}{u}}  and \mathrm{\frac{1}{v}} for a thin convex lens in order to determine its focal length is plotted as shown in the figure. The refractive index of lens is \mathrm{1.5} and its both the surfaces have same radius of curvature \mathrm{R. }The value of \mathrm{R} will be _________ \mathrm{\mathrm{cm}.}

\mathrm{\text { (where } u=\text { object distance, } v=\text { image distance) }}

Option: 1

10


Option: 2

-


Option: 3

-


Option: 4

-


Answers (1)

best_answer

By lens maker formula,
\mathrm{ \frac{1}{f}=(\mu -1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right) }

\mathrm{ R=R_1=R_2, \mu=1.5 }

\mathrm{ \therefore \frac{1}{f} =(\mu-1) \times \frac{2}{R_1}=\frac{1}{R} }

                        Or

\mathrm{\frac{1}{f}=(\mu-1) \times \frac{2}{R_2}=\frac{1}{R}}

From thr graph,

For, \mathrm{\frac{1}{\mu }=-0.10}

\mathrm{\frac{1}{v}=-0}

\mathrm{\frac{1}{v}-\frac{1}{u}=\frac{1}{f}=\frac{1}{R} }

\mathrm{0-(0.1)=\frac{1}{R}}

\mathrm{0 \cdot1=\frac{1}{R}}

\mathrm{\Rightarrow R=10\: cm}

The value of R will be \mathrm{10 \mathrm{~cm}}

Posted by

vishal kumar

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