If a charge $$q$$ is placed at the center of the line joining two equal charges $$Q$$ such that the system is in equilibrium then the value of $$q$$ is

If an ammeter is to be used in place of a voltmeter, then we must connect with the ammeter a

The kinetic energy needed to project a body of mass $$m$$ from the earth surface (radius $$R$$) to infinity is

Identify the pair whose dimensions are equal