Task: Text Categorization
Input (English): This quantity changes the refractive index of a material in the Kerr Effect. It splits spectral lines in the Stark Effect. The product of it and the magnetic field is the Poynting Vector. Its divergence equals charge density over permittivity by Gauss's Law. Equal to charge over (*) radius squared, it is measured in volts per meter. For 10 points, name this vector field symbolized capital E.
Output (English): Science