The radii of the inner and outer spheres of a condenser are 9 cm and 10 m respectively. If the dielectric constant of the medium between the two sphere is 6 and charge on the inner sphere is `18xx10^(-9)C`, then the potential of inner sphere will be, if the other sphere is earthed

Options

A. 180 V
B. 30 V
C. 18 V
D. 90 V

Answer

B

Explanation

Given, system is a spherical capacitor so, capacitance of system,
`C=K xx4piepsilon_(0)[(r_(1)r_(2))/(r_(2)-r_(1))]`
`=(6)/(9xx10^(9))[(9xx10)/(1)]xx10^(-2)=6xx10^(-10)F`
Now, potential of inner sphere will be equal to potential difference of the capacitor.
So, `V=(q)/(C)=(18xx10^(-9))/(6xx10^(-2))=30V`