The Verdet constant is a physical property of a material that describes how much the material will rotate the plane of polarization of light passing through it in the presence of a magnetic field. It is an important parameter in the study of magneto-optical effects, such as the Faraday effect, which is the rotation of the plane of polarization of light in a magnetic field. The Verdet constant is typically measured in units of degrees per unit length per unit magnetic field strength. Researchers study the Verdet constant to understand how different materials respond to magnetic fields and how they can be used in devices such as optical isolators and modulators.