We performed an experiment to measure the Faraday rotation of polarized light passing through a magnetic field, as well as measuring the Verdet constant of a glass tube with a length of 0.1 m. Linearly polarized light from a HeNe laser was sent through a magnetic field created by a solenoid. The light then passed through an adjustable polarizer and was detected by a photodiode. Using the photodiode, we measured how the intensity of the light changed when turning the polarizer through 360 degrees. We performed this experiment both with and without a glass tube inside the solenoid. We plotted the data as a function of voltage versus angle in plotly in order to find the angle where the voltage measured by the photodiode changed most rapidly. By keeping the polarizer at its most sensitive angle, we plotted voltage versus magnetic field and measured how the voltage changed with magnetic field. We used the lock-in amplifier to make the voltage measurement more accurate.