An electron rotates in a circle around a nucleus having positive charge Ze. Correct relation between total energy (E) of electron to its potential energy (U) is:\\
(1) $\mathrm{E} = \mathrm{U}$\\
(2) $2\mathrm{E} = \mathrm{U}$\\
(3) $2\mathrm{E} = 3\mathrm{U}$\\
(4) $\mathrm{E} = 2\mathrm{U}$