The radius of a metallic sphere if its capacitance is $1/9\,F$,is

The dielectric strength of air at $NTP$ is $3 \times 10^6 \, V/m$. The maximum charge that can be given to a spherical conductor of radius $3 \, m$ is:

The capacity of an isolated sphere is increased $n$ times when it is enclosed by an earthed concentric sphere. The ratio of their radii is

The stratosphere acts as a conducting layer for the Earth. If the stratosphere extends up to $50 \ km$ from the Earth's surface,calculate the capacitance of the spherical capacitor formed between the Earth's surface and the stratosphere in $F$. Take the radius of the Earth as $6400 \ km$.

Eight drops of mercury of equal radii combine to form a big drop. The capacitance of a bigger drop as compared to each smaller drop is (in $\times$)

The radii of the inner and outer spheres of a spherical capacitor are $9\,cm$ and $10\,cm$ respectively. If the dielectric constant of the medium between the two spheres is $6$ and the charge on the inner sphere is $18 \times 10^{-9}\,C$,calculate the potential of the inner sphere,given that the outer sphere is earthed.