# Electron in B Field - Quantum

by JesseC
Tags: electron, field, quantum
 P: 281 1. The problem statement, all variables and given/known data Magnetic field in xz plane. $$\vec{B}=\hat{i}B_x+\hat{k}B_z$$ Write down the hamiltonian operator for the interaction of the electron's intrinsic magnetic moment with this field and express it in matrix form. Find its eigenvalues and sketch these as a function of Bz, for fixed, nonzero Bx. How would the picture differ if Bx were zero. 3. The attempt at a solution So I got the hamiltonian looking like this: $$\hat{H}= \frac{e g_s}{2m_e} \hat{S} \cdot \vec{B}$$ I'm not sure about the form of $$\hat{S}$$ in this case? Is it a combination of z and x components? Normally if the field is just constant in the z-direction we could write B as a scalar and we'd just find the eigenvalues of the third pauli matrix.
 Emeritus Sci Advisor HW Helper Thanks PF Gold P: 11,379 It's all three components $$\hat{S} = \hat{i}S_x + \hat{j}S_y + \hat{k}S_z$$ Take the dot product as usual and then you can express the Hamiltonian as a linear combination of the Pauli matrices.
 P: 281 cheers for that, cleared it up.

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