A conducting sphere of radius R is given a charge Q. The electric potential and the electric field at the centre of the sphere rrespectively are

In a region, the potential is represented by V(x, y, z) = 6x $$-$$ 8xy $$-$$ 8y + 6yz,   where $$V$$ is in volts and x, y, z are in metres. The electric force experienced by a charge of 2 coulomb situated at point (1, 1, 1) is

An electric dipole of dipole moment p is aligned parallel to a uniform electric field E. The energy required to rotate the dipole by 90^o is

A charge q is placed at the centre of the line joining two equal charges Q. The system of the three charges will be in equilibrium if q is equal to