Ning Zhu edited subsection_Lock_in_Method_A__.tex  over 8 years ago

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\subsection{ Lock-in Method}  A third method for finding the Verdet constant of a material involves using a lock-in amplifier to better read the signal from the photodiode. The %The  lock-in we used was set at a frequency range was 100 Hz and the fine frequency range adjustment was 10 Hz. The lock-in amplifier had a gain of 10, the pre-amplifier a gain of 500, the bandpass filter a gain of 2, and the low pass filter a gain of 1.We 1. We  used a function generator to sinusoidally drive the voltage going into the solenoid, using a frequency of 100 Hz. We varied the RMS value of the AC voltage which was driving the solenoid and recorded the RMS value of the corresponding varying photodiode voltage. The big idea of the calculation associated with this method is illustrated in Equation \ref{bigidea} :  \begin{equation}  \label{bigidea} 

I_{rms}=0.6137\times V_{rms}  \end{equation}  %$$B=11.1\times\frac{mT}{A}\times I$$  $V_{pd, RMS}$ represents the aforementioned RMS value of photodiode voltage. $\frac{d\theta}{dV_{pd}}$ is the same as in method 2. \newline  We applied four different magnetic fields so we ended up with four Verdet constants. We took the average and used the maximum and minimum to calculate the uncertainty.  In this way, we get: $$V_{c}=20.43\pm0.058\frac{radians}{T \cdot m}$$  %$$Gain=G_{preamplifier}\times G_{filter}\times G_{lock-in-amplifier}\times G_{lowpass filter}=500\times2\times10\times1=10000$$  %$$V_{Photodiode}=\frac{V_{output}\times1.11}{10000}$$