In a transmission line, one form of this quantity equals one over the square root of the line inductance times the line (-5[1])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 (15[1])wavenumber, while another form of this (-5[1])quantity changes with (*) frequency in dispersive (-5[1])media. (-5[1])Del-squared u (10[3])times this quantity squared equals the second time derivative of u in the wave (-5[1])equation. The ratio of (-5[1])the “phase” form of this (10[1])quantity in a (10[1])medium and a (10[1])vacuum equals (10[1])the (10[1])index of refraction. For 10 (10[3]-5[1])points, name this quantity equal to frequency times (10[1])wavelength, with units of meters per second. (10[8]0[2])■END■