 and u is the magnetic permeability, which equals Mr M0, the relative permeability multiplied by the permeability of free space. EVE = 0 (7.5) (7.6) (7.7) (7.8) Elimination of H from this set of simultaneous equations produces a wave equation, as in equation 7.9. (7.9) Equally, E could have been eliminated to give equation 7.10. (7.10) If E or H is disturbed at a point within a homogeneous nonconductive medium, a "wave" is produced, which propagates away from the point with a velocity of V meters/sec. When this disturbance is a sinusoidal oscillation of frequency f hertz, the wave equations may be solved for a general wave front of any shape by considering it to be composed of set of plane waves. One of these plane waves can be expressed in a Cartesian frame, such that it progresses along the Z axis with the electric field along the Y axis. Then it has a solution, at time t, proportional to equation 7.11, where is 2 divided by the wavelength in meters. e-j(Z-vt)B (7.11) Analysis shows that this plane wave has its magnetic component along the X axis; that is, the electric vector is at right angles to the magnetic vector, and both are perpendicular to the direction of propagation. The velocity is given by equation 7.12. Fundamental Laws of Electromagnetism (7.12) If the relative permittivity and permeability are both unity, V is the velocity of the wave in free space, C, and a is the free space wavelength, A0. The value of is defined as (4)10-7 Henry per meter, and measurements have set E at (8.8547)10-12 Farad per meter. This leads to a velocity of the wave in free space of (2.998)108 meters per second. This is the same as the velocity determined by direct measurement, at least within the limits of experimental error. For most practical purposes it is adequate to take this velocity to be equal to 3.108 meters per second. The refractive index of a medium is defined by equation 7.13. (7.13) By analogy to Ohm's law, the impedance of the medium is given by equation 7.14. (7.14) For free space this impedance is equal t