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Capacitance of an isolated conducting sphere of radius \mathbf{R}_{1} becomes \mathrm{n} times when it is enclosed by a concentric conducting sphere of radius \mathbf{R}_{2} connected to earth. The ratio of their radii \mathrm{\left(\frac{R_{2}}{R_{1}}\right)} is :

 

Option: 1

\mathrm{\frac{n}{n-1} \\ }


Option: 2

\mathrm{\frac{2n}{2n+1}}


Option: 3

\mathrm{\frac{n+1}{n}}


Option: 4

\mathrm{\frac{2n+1}{n}}


Answers (1)

best_answer

Case I

Capacitance of an isolated conducting sphere of radius \mathrm{R_{1}}

\mathrm{C_{1}=4\pi \varepsilon _{0}R_{1}}\rightarrow (1)

Case II

\mathrm{C_{2}=\frac{4\pi \varepsilon _{0}}{(\frac{1}{R_{1}}-\frac{1}{R_{2}})}}\rightarrow (2)

It is given that ,

\mathrm{C_2 =n C_1 }

\mathrm{\frac{4 \pi \varepsilon_0}{\frac{1}{R_1}-\frac{1}{R_2}} =n 4 \pi \varepsilon_0 R_1 }

\mathrm{\frac{R_1 R_2}{R_2-R_1} =n R_1 }

\mathrm{R_2 =n R_2-n R_1 }

\mathrm{n R_1 =(n-1) R_2 }

\mathrm{ \frac{R_2}{R_1}=\frac{n}{n-1}}

Hence (1) is correct option

Posted by

Nehul

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