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Time taken by light to travel in two different materials \mathrm{A \, and\: \mathrm{B}} of refractive indices \mu_{\mathrm{A}}$ and $\mu_{B} of same thickness is \mathrm{t_{1} \: and\: t_{2}}  respectively. If \mathrm{t_{2}-t_{1}=5 \times 10^{-10} s} and the ratio of \mathrm{\mu_{A} \: to\: \mu_{B} \: is \: 1: 2}. Then, the thickness of material, in meter is : (Given v_{\mathrm{A}}$ and $v_{\mathrm{B}} are velocities of light in  \mathrm{A}$ and $\mathrm{B} materials respectively.)
 

Option: 1

5 \times 10^{-10} v_{\mathrm{A}} \mathrm{m}


Option: 2

5 \times 10^{-10} \mathrm{~m}


Option: 3

1.5 \times 10^{-10} \mathrm{~m}


Option: 4

5 \times 10^{-10} v_{\mathrm{B}} \mathrm{m}


Answers (1)

best_answer

Let the thickness of material be d

From Snell's law,

\mathrm{\frac{\mu_A}{\mu_B}=\frac{V_B}{V_A}=\frac{1}{2} }

\mathrm{\frac{V_B}{V_A}=\frac{d / t_2}{d / t_1}=\frac{1}{2} }

             \mathrm{\frac{t_1}{t_2}=\frac{1}{2} }

             \mathrm{\frac{t_2}{t_1}=\frac{2}{1}}

             \mathrm{\frac{t_2-t_1}{t_1}=1 }

             \mathrm{t_1=5 \times 10^{-10} \mathrm{~s} }

              \mathrm{V_A=\frac{d}{t_1} }

              \mathrm{d=V_A t_1=(5 \times10^{-10})V{_{A}}}

Hence (1) is correct option

Posted by

manish painkra

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