Question

A very small sphere of mass 80 g having a charge q is held at a height 9 m vertically above the centre of a fixed conducting sphere of radius 1m, carrying an equal charge q. When released it falls until it is repelled just before it comes in contact with the sphere. Calculate the charge q. [g = 9.8 m/s²]

 

Answer 1

Keeping in mind that here both electric and gravitational potential energy are changing and for external point a charged sphere behaves as whole of its charge were concentrated at its applying conservation of energy between initial and final position, we have