7. A plane monochromatic electromagnetic wave propagating in free space is incident normally on the plane of the surface of a medium of the index of refraction n. Relative to a stationary observer, the electric field of the incident wave is given by the real part of Efei(kz-wt), where z is the coordinate along the normal to the surface. Obtain the frequency of the reflected wave in the case that the medium and its surface are moving with velocity v along the positive z- direction, with respect, with respect the observer. 7. A plane monochromatic electromagnetic wave propagating in free space is incident normally on the plane of the surface of a medium of the index of refraction n. Relative to a stationary observer, the electric field of the incident wave is given by the real part of Efei(kz-wt), where z is the coordinate along the normal to the surface. Obtain the frequency of the reflected wave in the case that the medium and its surface are moving with velocity v along the positive z- direction, with respect, with respect the observer