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Prove Kramers' relation:

sn2rs-(2s+1)ars-1+s4[(2l+1)2-s2]a2rs-2=0

Which relates the expectation values of rto three different powers (s,s-1,ands-2),for an electron in the state n/mof hydrogen. Hint: Rewrite the radial equation (Equation) in the form

u''=[l(l+1)r2-2ar+1n2a2]u

And use it to expressrole="math" localid="1658192415441" (ursu'')drin terms of (rs),(rs-1)and(rs-2). Then use integration by parts to reduce the second derivative. Show that (ursu'')dr=-(s/2)(rs-1)and(u'rsu')dr=-[2/s+1](u''rs+1u')dr. Take it from there.

Short Answer

Expert verified

The proved Kramer鈥檚' relation of equation

rs-2a2s4(2l+1)2-s2-(2s+1)ars-1+s+1n2rs=0

Step by step solution

01

Determine the formula for Kramer's relation

The Kramer鈥檚' relation is a relationship between the anticipated values of "nearby" powers of r for the hydrogen atom, named after the Dutch scientist Hans Kramers:

s+1n2rs-(2s+1)ars-1+a2s4(2l+1)2-s2rs-2=0

02

use the Bohr radius to rewrite the radial portion of the Schrodinger equation

Need to establish a relation:

s+1n2rs-(2s+1)ars-1+a2s4(2l+1)2-s2rs-2=0

Which is equal to a=4蟺蔚o2me2. Radial part of Schrodinger equation:

-u''+-e2402m21r+l(l+1)r2u=E2m2uE=-m22e2401n2-u''+-2ar+l(l+1)r2u=-1a2n2uu''=2ar+l(l+1)r2+1a2n2u

Calculate the following integral using the given hint:

(ursu'')dr=urs-2ar+l(l+1)r2+1a2n2udr=-2aurs-1udr+l(l+1)urs-2udr+1a2n2ursudr=-2ars-1+l(l+1)rs-2+1a2n2rs

But I'm still stumped on the left-hand side of the equation. Use partial integration in this case:

(ursu'')dr=ursu'|0-ddr(urs)u'dr=-(u'rs+surs-1u'dr=-u'rsu'dr-surs-1u'dr

And you'll have to do it twice more for these new unknown integrals:

ursu'dr=-ddr(urs)udr=-u'rsudr-srs-1

u'rsudr=ursu'drBecause radial functions are real, not complex.

2u'rsudr=-srs-1ursu'dr=-s2rs-1

03

Calculate first integral in equation u'rsu'dr-s  urs-1u'dr

In the equation, the first integral must be calculated. This is how we go about it:

(u''rs+1u')dr=-u'ddr(rs+1u')dr=-(s+1)u'rsu'dr-u'rs+1u''dr2(u''rs+1u')dr=-(s+1)u'rsu'dr

u'rsu'dr=-2s+1(u''rs+1u')dr

u''=-2ar+l(l+1)r2+1a2n2uu'rsu'dr=-2s+1-2ar+l(l+1)r2+1a2n2urs+1u'dr=-2s+1-2aursu'dr+l(l+1)urs-1u'dr+1a2n2urs+1u'dr

Using equation get:

u'rsu'dr=-2/s+1)sars-1+l(l+1)-s-12rs-2-1a2n2s+12rs=-2ass+1rs-1+s-1s+1l(l+1)rs-2+1n2a2rs

Equation on second page is:

(ursu'')dr=-u'rsu'dr-surs-1u'dr

On the left hand side, there is an equation from the second page, and on the right hand side, there are equations from the third page and an equation from the second page. All of those equations are now inserted into the previous expression:

-2ars-1+l(l+1)rs-2+1a2n2rs=2ass+1rs-1-s-1s+1l(l+1)rs-2-1n2a2rs+s(s-1)2rs-2rs-2l(l+1)1+s-1s+1-ss-12rs-1ss+1+1+2a2n2rs=0rs-2l(l+1)2ss+1-ss-122ar12s+1s+1+2a2n2rs=0a2(s+1)2

rs-2a2l(l+1)s-s(s2-1)4-(2s+1)ars-1+s+1n2rs=0rs-2a2s4(2l+1)2-s2-(2s+1)ars-1+s+1n2rs=0

The proved Kramer鈥檚' relation of equation

rs-2a2s4(2l+1)2-s2-(2s+1)ars-1+s+1n2rs=0

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Most popular questions from this chapter

Van der Waals interaction. Consider two atoms a distanceapart. Because they are electrically neutral you might suppose there would be no force between them, but if they are polarizable there is in fact a weak attraction. To model this system, picture each atom as an electron (mass m , charge -e ) attached by a spring (spring constant k ) to the nucleus (charge +e ), as in Figure. We'll assume the nuclei are heavy, and essentially motionless. The Hamiltonian for the unperturbed system is

H0=12mp12+12kx12+12mp22+12kx22[6.96]

The Coulomb interaction between the atoms is

H'=14蟺系0(e2R-e2R-x1-e2R+x2+e2R-x1+x2 [6.97]

(a) Explain Equation6.97. Assuming that localid="1658203563220" |x1| and |x2|are both much less than, show that

localid="1658203513972" H'-e2x1x220R3 [6.98]

(b) Show that the total Hamiltonian (Equationplus Equation) separates into two harmonic oscillator Hamiltonians:

H=[12mp+2+12(k-e220R3x+2]+[+12mp-2+12(k+e220R3x-2] [6.99]

under the change of variables

x12(x1x2) Which entails p=12(p1p2) [6.100]

(c) The ground state energy for this Hamiltonian is evidently

E=12(++-) Where =k(e2/20R3)m [6.101]

Without the Coulomb interaction it would have been E0=0, where 0=k/m. Assuming that, show that

VE-E0-8m203(e220)21R6. [6.102]

Conclusion: There is an attractive potential between the atoms, proportional to the inverse sixth power of their separation. This is the van der Waals interaction between two neutral atoms.

(d) Now do the same calculation using second-order perturbation theory. Hint: The unperturbed states are of the form n1(x1)n2(x2), where n(x)is a one-particle oscillator wave function with mass mand spring constant k;Vis the second-order correction to the ground state energy, for the perturbation in Equation 6.98 (notice that the first-order correction is zero).

By appropriate modification of the hydrogen formula, determine the hyperfine splitting in the ground state of

(a) muonic hydrogen (in which a muon-same charge and g-factor as the electron, but 207times the mass-substitutes for the electron),

(b) positronium (in which a positron-same mass and g-factor as the electron, but opposite charge-substitutes for the proton), and

(c) muonium (in which an anti-muon-same mass and g-factor as a muon, but opposite charge-substitutes for the proton). Hint: Don't forget to use the reduced mass (Problem 5.1) in calculating the "Bohr radius" of these exotic "atoms." Incidentally, the answer you get for positronium (4.8210-4eV)is quite far from the experimental value; (8.4110-4eV)the large discrepancy is due to pair annihilation (e++e-+), which contributes an extra localid="1656057412048" (3/4)螖贰,and does not occur (of course) in ordinary hydrogen, muonic hydrogen, or muoniun.

When an atom is placed in a uniform external electric field ,the energy levels are shifted-a phenomenon known as the Stark effect (it is the electrical analog to the Zeeman effect). In this problem we analyse the Stark effect for the n=1 and n=2 states of hydrogen. Let the field point in the z direction, so the potential energy of the electron is

H's=eEextz=eEextrcos

Treat this as a perturbation on the Bohr Hamiltonian (Equation 6.42). (Spin is irrelevant to this problem, so ignore it, and neglect the fine structure.)

(a) Show that the ground state energy is not affected by this perturbation, in first order.

(b) The first excited state is 4-fold degenerate: Y200,Y211,Y210,Y200,Y21-1Using degenerate perturbation theory, determine the first order corrections to the energy. Into how many levels does E2 split?

(c) What are the "good" wave functions for part (b)? Find the expectation value of the electric dipole moment (pe=-er) in each of these "good" states.Notice that the results are independent of the applied field-evidently hydrogen in its first excited state can carry a permanent electric dipole moment.

Consider the (eight) n=2states, |2ljmj. Find the energy of each state, under weak-field Zeeman splitting, and construct a diagram like Figure 6.11 to show how the energies evolve asBext increases. Label each line clearly, and indicate its slope.

Find the (lowest order) relativistic correction to the energy levels of the one-dimensional harmonic oscillator. Hint: Use the technique in Example 2.5 .

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