Chapter 4: Q53P (page 195)
Work out the spin matrices for arbitrary spin , generalizing spin (Equations 4.145 and 4.147), spin 1 (Problem 4.31), and spin (Problem 4.52). Answer:
where,
Short Answer
The spin matrices are,
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Chapter 4: Q53P (page 195)
Work out the spin matrices for arbitrary spin , generalizing spin (Equations 4.145 and 4.147), spin 1 (Problem 4.31), and spin (Problem 4.52). Answer:
where,
The spin matrices are,
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[Refer to Problem 4.59 for background.] In classical electrodynamics the potentials Aandare not uniquely determined; 47 the physical quantities are the fields, E and B.
(a) Show that the potentials
(whereis an arbitrary real function of position and time). yield the same fields asand A. Equation 4.210 is called a gauge transformation, and the theory is said to be gauge invariant.
(b) In quantum mechanics the potentials play a more direct role, and it is of interest to know whether the theory remains gauge invariant. Show that
satisfies the Schr枚dinger equation (4.205) with the gauge-transformed potentialsand, Sincediffers fromonly by a phase factor, it represents the same physical state, 48and the theory is gauge invariant (see Section 10.2.3for further discussion).
Consider the observablesand .
(a) Construct the uncertainty principle for
(b) Evaluate in the hydrogen state .
(c) What can you conclude aboutin this state?
Determine the commutator of with(where) Generalize your result to show that
Comment: Because does not commute with , we cannot hope to find states that are simultaneous eigenvectors of both. In order to form eigenstates ofweneed linear combinations of eigenstates of. This is precisely what the Clebsch-Gordan coefficients (in Equation 4.185) do for us, On the other hand, it follows by obvious inference from Equation 4.187that the sumrole="math" localid="1655980965321" does commute withdata-custom-editor="chemistry" , which is a special case of something we already knew (see Equation 4.103).
(a) Construct the spatial wave function for hydrogen in the state Express your answer as a function of (the Bohr radius) only鈥攏o other variables (etc.) or functions (etc.), or constants (etc.), or derivatives, allowed (蟺 is okay, and e, and 2, etc.).
(b) Check that this wave function is properly normalized, by carrying out the appropriate integrals over,
(c) Find the expectation value of in this state. For what range of s (positive and negative) is the result finite?
The raising and lowering operators change the value of m by one unit:
(4.120).
Where are constant. Question: What is , if the Eigen functions are to be normalized? Hint: First show thatis the Hermitian conjugate of (Since are observables, you may assume they are Hermitian鈥ut prove it if you like); then use Equation 4.112.
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