In a tandem accelerator the particle is accelerated twice by the same voltage, so the output energy is ( 1 + q ) V , as the anion form is singly charged. If the charge q is in conventional units of coulombs and the potential V is in volts the particle energy will be given in joules. However, because the charge on elementary particles is so small (the charge on the electron is 1.6x10 coulombs), the energy in joules is a very small number.