Dielectric strength of air is `3xx10^6 V m^-1`. If electric potential on a sphere can be `9xx10^6V`, then find the minimum radius of the sphere.

In a Van de Graaff type generator a spherical metal shell is to be a 15 xx 10^6 V electrode. The dielectric strength of the gas surrounding the electrode is 5 xx 10^7 Vm^-1 . What is the minimum radius of the spherical shell required? (You will learn from this exercise why one cannot build an electrostatic generator using a very small shell which requires a small charge to acquire a high potential.)

A parallel plate capacitor is to be designed with a voltage rating 1 kV, using a material of dielectric constant 3 and dielectric strength about 10^7 Vm^-1 . (Dielectric strength is the maximum electric field a material can tolerate without breakdown, i.e., without starting to conduct electricity through partial ionisation.) For safety, we should like the field never to exceed, say 10% of the dielectric strength. What minimum area of the plates is required to have a capacitance of 50 pF?

An electron is circulating around the nucleus of a hydrogen ato in a circular orbit of radius 5.3 cxx10^-11 m. Calculate the electric potential energy of the atom in eV. What would be the electric potential due to a helium nucleus at the same radius. Given, that (4piepsilon_0)^-1 = 9xx10^9 m F^-1 and e = 1.6 xx 10^-19 C .

Metallic spheres of radii 6 cm, 8 cm and 10 cm, respectively, are melted to form a single solid sphere. Find the radius of the resulting sphere.

A hollow metal sphere of radius 5 cm is charged, such that the potential on its surfae is 10 V. The potential at the centre of the sphere is

A hollow metallic sphere of radius 10 cm is charged, such that potential of its surface is 70 V. The potential at the centre of the sphere would be

The electric potential at the surface of an atomic nucleus (Z=50) of radius 9.0 xx 10^-15 m is