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ehrenfest
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[SOLVED] energies of spin states
An electron is in a constant magnetic field with magnitude B_0, aligned in the -z direction. My book says without explanation:
"the spin-up state has energy [itex] -\mu_B B_0[/itex]"
where [itex] \mu_B[/itex] is the Bohr magneton
I looked back in the Spin Angular Momentum chapter and I cannot find where this was derived.
I am thinking that they used the equation [tex] H = B_0 \mu_B \sigma_z [/itex] and just calculated the energy of the spin up state using the TISE and the vector representation of spin-up in z. Is there an a priori way of knowing the energy of a spin state of it is spin up or down in x, y,or z in a magnetic field?
EDIT: OK. So I think that if you actually calculate the energies for the spins using H |\psi> = E | \psi>, you get that the energy is always [itex] -\mu_B B_0[/itex] when the spin is antiparallel to the magnetic field vector and [itex] \mu_B B_0[/itex] when the spin is parallel to the magnetic field vector. I explicitly checked that this holds for x, y, and z. Could I have obtained this result without calculating with Pauli matrices, though? Does this result hold when the spin and magnetic field are parallel but not along x,y,z,-x,-y,-z?
Homework Statement
An electron is in a constant magnetic field with magnitude B_0, aligned in the -z direction. My book says without explanation:
"the spin-up state has energy [itex] -\mu_B B_0[/itex]"
where [itex] \mu_B[/itex] is the Bohr magneton
I looked back in the Spin Angular Momentum chapter and I cannot find where this was derived.
I am thinking that they used the equation [tex] H = B_0 \mu_B \sigma_z [/itex] and just calculated the energy of the spin up state using the TISE and the vector representation of spin-up in z. Is there an a priori way of knowing the energy of a spin state of it is spin up or down in x, y,or z in a magnetic field?
EDIT: OK. So I think that if you actually calculate the energies for the spins using H |\psi> = E | \psi>, you get that the energy is always [itex] -\mu_B B_0[/itex] when the spin is antiparallel to the magnetic field vector and [itex] \mu_B B_0[/itex] when the spin is parallel to the magnetic field vector. I explicitly checked that this holds for x, y, and z. Could I have obtained this result without calculating with Pauli matrices, though? Does this result hold when the spin and magnetic field are parallel but not along x,y,z,-x,-y,-z?
Homework Equations
The Attempt at a Solution
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