Task: Text Categorization
Input (English): For an undulator, the most prominent value for this quantity is proportional to the Lorentz gamma\n squared over the sum one plus the product of the Lorentz gamma squared and the angle squared. For\n alternating current in a conductor, the skin depth is given by the square root of the quantity two over the\n product of permeability, conductivity, and this quantity. The levels of the quantum harmonic oscillator are\n quantized in discrete units of this quantity. The energy of a photon is given by Planck's constant times this\n quantity, and for a pendulum, this quantity is given by the square root of the gravitational acceleration over\n the length. For ten points, identify this quantity in physics which is the inverse of the period and has units\n of inverse seconds, or hertz.
Output (English): Science