Speed of Light

# In your study of mechanical waves you may have

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Unformatted text preview: m bounce back. In your study of mechanical waves, you may have learned that an upward (positive) wave pulse that hits a rigid wall will bounce back in the downward (negative) position; if the wall isn't rigid, then the energy is dissipated and the wave pulse is made to die (“terminated”) at the wall. Such terminators reduce or eliminate the reflected wave; this is important because, as you've seen, reflected waves interfere with incident waves and cause weakening or corruption of the original signal. In today's lab, you will use a terminating resistor to minimize such reflections; you will also learn that the impedance (the AC equivalent of resistance) of this terminator and the impedance of the wire used must be matched in order to minimize signal reflection and hence maximize signal transfer. *Faster Than Light? Note that there are situations where motion faster than the speed of light occurs, however, no matter, energy or information actually travels greater than the speed of light. For example, imagine that you are holding a powerful laser pointer aimed at the Moon. If you rotate the laser, the projected spot will travel at a speed given by v= r as measured by an observer on the moon. As the distance to the moon is large, it is easy to see that even slight rotation of the wrist can result in the projected spot moving at a speed greater than the speed of light. Upon closer analysis, however, the spot traveling across the moon is not composed of the same photons (particles of light) but in fact different photons from the same light source on Earth. Therefore, there are no particles, no energy, and no information that are actually moving faster than the speed of light. If you can think of a scheme to transmit information faster than c, the Nobel committee might want to have a talk with you! Theory Speed of Propagation The speed of light can be calculated using the familiar relationship, c= x ; however, since the two t signals as displayed on the oscilloscope travel not only through air (you will be measuring this distance) but also through the coaxial cable, you will have to account for thi...
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