We have seen that in a magnetic field, the magnetic moment of an electron couples to an external magnetic field B to give the so-called Zeeman term H_Z=-gμB. Bzsz where for free electrons the factor g we have introduced is called the g-value and is given without quantum field corrections by g=-2 and with corrections by g  =-2.0023. In a medium the spin-orbit coupling can change the effective value of g called  lso the Lande’s g-value. In an electron spin resonance experiment (ESR), the spins of electrons in a magnetic field can be flipped by photon absorption. Calculate the energy of a photon needed to change the spin direction of an electron from down to up in a  agnetic field of 0.3 T and a g-value of 2.35.