A lossless transmission line is characterized by the surge impedance and surge velocity . When the transmission line is energized by a voltage source , a forward surge is created (the magnitude: , where is the input circuit impedance). The surge reaches the other end in the transit time , being the line length. Then, a backward surge is generated by the reflection factor , being the output impedance. This wave generates another forward surge by the factor at the initial terminal. The voltage and current in the transmission line are described by the superposition of those successive forward and backward components and .