In a transmission line, one form of this quantity equals one over the square root of the line inductance times the line capacitance. Single-mode optical fibers are preferred in long-distance communication since they avoid distortion from this quantity changing with polarization. One form of this quantity equals the derivative of angular frequency with respect to wavenumber, while another form of this quantity changes with (*) frequency in dispersive media. Del-squared u times this quantity squared equals the second time derivative of u in the wave equation. The ratio of the “phase” form of this quantity in a medium and a (10[1])vacuum equals the (10[1])index of refraction. For 10 (10[1])points, name this quantity equal to frequency times wavelength, with units of meters per second. ■END■