If the Hamiltonian of a two-electron system is independent of the electron spins, the eigen energy of the system (a) is independent of the electron spins. (b) depends on the electron spins

when insulating materials rub against each other, they may become electrically charged . electrons , which are negatively charged, may be 'rubbed off' one material and on to the other. the material that gains electrons becomes negatively charged. the material that loses electrons is left with a positive charge.

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