... conservation of energy and momentum.density of modes The number of modes of the radiation field in an energy range dE. Thedensity of modes is a function of the boundaryconditions ofthe spaceunder ... single point particlein three-dimensional space has three degrees of freedom; a system of N point particles has 3Ndegrees of freedom.De Haas–Van Alphan effect In 1 930 , DeHaas and Van Alphan ... transitions, theEinstein coefficient is given byAν=16π 3 ν 3 3ε0hc 3 g2Sedelectric dipole transitionsAν=16π 3 µ0ν 3 3hc 3 g2Smdmagnetic dipole transitionsAν=8π5ν55ε0hc5g2Seqelectric...