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(a) A particle of spin1and a particle of spin 2 are at rest in a configuration such that the total spin is 3, and its z component is . If you measured the z component of the angular momentum of the spin-2particle, what values might you get, and what is the probability of each one?

(b) An electron with spin down is in the state510of the hydrogen atom. If you could measure the total angular momentum squared of the electron alone (not including the proton spin), what values might you get, and what is the probability of each?

Short Answer

Expert verified

(a) 2with a probability equal to 1/15 , or with a probability of 8/15 or with a probability of 6/15 .

(b) The total is 3/2 or 1/2 withl(l+1)2=1542 and 342respectively. Also, for 1542the probability is 2/3 , and for 342it is 1/3 .

Step by step solution

01

Definition of Probability

The probability of an event occurring. The proportion of the total number of conceivable outcomes to the number of options in an exhaustive collection of equally likely outcomes that cause a given occurrence.

02

(a) Solve the total spin is 3, and its z  component is ℏ

Expand the composite spin 3,1>from the individual spins. For spin 2, the expected states are as follows,

|2,2>,|2,1>,|2,0>,|2,-1>, and 2,-2>.

Write the possible states for spin 1.

localid="1658127583657" |1,1>,|1,0>,and1,-1>.

The combinations that have a z projection equal to one are needed, so the expansion can be written as follows,

|3,1=|2,2>|1,-1>+|2,1>|1,0>+|2,0>|1,1

Determine the three expansion coefficients a , and in the Clebsch-Gordon tables. Then the probabilities are ||2,||2 and 2.

Return to the Clebsch-Gorden table and using the equation.

|sm=cm1m2mm1+m2=ms1s2s|s1m1>|s2m2>

Write the outcomes using the above information.

|31=115|22>|1-1>+815|21>|(100)+615|2011

Thus, 2 is obtained with a probability equal to 1/15 , orwith a probability of 8/15 or with a probability of 6/15 .

03

(b) Determination of the total angular momentum squared of the electron

Look the table 11/2 and write the outcome.

|10|12-12=2334-12+1312-12

So the total is 3/2 or 1/2 with l(l+1)2=1542and 342respectively.

Thus, for 1542the probability is 2/3 , and for 342it is 1/3 .

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Most popular questions from this chapter

(a) Construct the wave function for hydrogen in the state n=4,I=3,m=3. Express your answer as a function of the spherical coordinates r,and.

(b) Find the expectation value of role="math" localid="1658391074946" rin this state. (As always, look up any nontrivial integrals.)

(c) If you could somehow measure the observable Lx2+Ly2on an atom in this state, what value (or values) could you get, and what is the probability of each?

(a) Using Equation 4.88, work out the first four Laguerre polynomials.

(b) Using Equations 4.86, 4.87, and 4.88, find v(), for the case n=5,I=2.

(c) Find v()again (for the case role="math" localid="1658315521558" n=5,I=2), but this time get it from the recursion formula (Equation 4.76).

Lq(x)=eqq!(ddx)q(e-x-x9)(4.88)v()=Ln-2l+1l-1(4.86)Lqp(x)(-1)pddxLp+q(x)(4.87)cj+1=2(j+l+1-n)(j+1)(j+2l+2)cj(4.76)

Quarks carry spin 1/2. Three quarks bind together to make a baryon (such as the proton or neutron); two quarks (or more precisely a quark and an antiquark) bind together to make a meson (such as the pion or the kaon). Assume the quarks are in the ground state (so the orbital angular momentum is zero).

(a) What spins are possible for baryons?

(b) What spins are possible for mesons?

A hydrogen atom starts out in the following linear combination of the stationary states n=2, l=1, m=1 and n=2, l=1, m=-1.

(r,0)=12(211+21-1)

(a) Construct(r,t)Simplify it as much as you can.

(b) Find the expectation value of the potential energy,<V>. (Does it depend on t?) Give both the formula and the actual number, in electron volts.

An electron is in the spin state

=A3i4

(a) Determine the normalization constant .

(b) Find the expectation values of Sx,Sy , and Sz.

(c) Find the "uncertainties" ,Sx , SyandSz . (Note: These sigmas are standard deviations, not Pauli matrices!)

(d) Confirm that your results are consistent with all three uncertainty principles (Equation 4.100 and its cyclic permutations - only with in place ofL, of course).

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