Electromagnetic Waves“REFLECTION, DIFRACTION & SCATTERING”
...lects the image of the observer. Reflection occurs when a wave incident on a boundary is forced to return into the medium in which it was originally traveling. When a plane wave strikes a plane interface between media, the wave in general is partly transmitted, partly reflected. Such a problem is solved by assuming an incident and reflected wave in the first medium, and a transmitted wave only in the second medium. The angle of incidence is the angle between the normal to the interface and wave vector of the incident wave. The angle of reflection is the similar angle for the reflected wave. The directions of propagation must lie in the same plane, the plane of incidence, and the angle of incidence equals the angle of reflection. The wave vector of the transmitted, or refracted, wave also lies in the plane of incidence, and the ratio of the sine of the angle of incidence to sine of the angle of refraction is the same as the ratio of the propagation velocities. Reflection may occur with large objects ,such as surface of earth ,buildings and walls. Diffraction: A radio wave that meets an obstacle has a natural tendency to bend around the obstacle. The bending, called diffraction, results in a change of direction of part of the wave energy from the normal line-of-sight path. This change makes it possible to receive energy around the edges of an obstacle as shown in view A or at some distances below the highest point of an obstruction. Although diffracted rf energy usually is weak, it can still be detected by a suitable receiver. The principal effect of diffraction extends the radio range beyond the visible horizon. In certain cases, by using high power and very low frequencies, radio waves can be made to encircle the Earth by diffraction. Diffraction is when a wave goes through a small hole and has a flared out geometric shadow of the slit. Diffraction is a characteristic of waves of all types. We can hear around a corner because of the diffraction of sound waves. For instance, if a wall is next to you when you yell, the sound will parallel the wall. The wall may stop, but the voice doesn't; sound will almost turn the corner of the wall. This is diffraction. Radio wave energy may be blocked by obstacles such as buildings and hills, or it may diffract around the obstacles. Radio waves with longer wavelengths and lower frequencies are more likely to be diffracted around these sorts of landscape features. Obstacles, known as 'clutter', may be useful shields, preventing radio signals fr...