Lecture (20 minutes)

Notes on and illustrations of attenuation in waves atten_wiki.ppt

The students have studied attenuation in the context of oscillators, and the intent here is to have them work out the details as an independent exercise. The purpose is to enable them to confront their experimental results of reflection of waves at the boundary of two coaxial cables. In the experiment, the amplitude of the reflected pulse is different not only because of impedance mismatch, but also because of energy loss in the cable. These contributions must be separately modeled.

It is helpful to set up the attenuation discussion in the context of the rope as shown in the notes. Only the case of light damping is discussed, which has the practical (and helpful) consequence that the amplitude of the wave is indeed attenuated over the long distances of the cables used in the lab, but the reflection and transmission coefficients are very little altered by the light damping. Take the students only as far as you feel is necessary to keep them from becoming frustrated.

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