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Unformatted text preview: Supplemental Note: Utilizing a Lock-In Amplifier for the Faraday Rotation Experiment Experiments in Modern Physics (P451) In order to measure the Faraday rotation effect, one needs to measure small changes in the intensity of a laser passing through a medium (water in the case of this lab) that is polarized by a solenoid. Detection of the beam intensity is done with a photodiode. The difficulty with this experiment is that the detector detects both the beam and the ambient light in the room variations in this background due to varying illumination of the apparatus often exceeds the size of the experimental effect that is under study. In order to allow extraction of the component of the signal due to the beam only an optical chopper and lock-in amplifier is used. The chopper introduces a time structure (about 40 Hz or 80 Hz depending on switch position) into the beam. Therefore the signal that one needs to isolate is modulated at this frequency on top of some steady state background due to ambient light that one would like to remove. The lock-inon top of some steady state background due to ambient light that one would like to remove....
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- Fall '09