The process of coherent creation of particle - hole excitations by an electric field in graphene is quantitatively described. We calculate the evolution of current density, number of pairs and energy after switching on the electric field. In particular, it leads to a dynamical visualization of the universal finite resistivity without dissipation in pure graphene. We show that the DC conductivity of pure graphene is π/2 e²/h rather than the often cited value of 4/π e²/h. A crossover from linear response to non-linear response as well as the possibility of Bloch oscillations is discussed.