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Question: The most prominent feature of the hydrogen spectrum in the visible region is the red Balmer line, coming from the transition n = 3to n = 2. First of all, determine the wavelength and frequency of this line according to the Bohr Theory. Fine structure splits this line into several closely spaced lines; the question is: How many, and what is their spacing? Hint: First determine how many sublevels the n = 2level splits into, and find Efs1for each of these, in eV. Then do the same for n = 3. Draw an energy level diagram showing all possible transitions from n = 3to n = 2. The energy released (in the form of a photon) is role="math" localid="1658311193797" (E3-E2)+E, the first part being common to all of them, and the E(due to fine structure) varying from one transition to the next. Find E(in eV) for each transition. Finally, convert to photon frequency, and determine the spacing between adjacent spectral lines (in Hz- -not the frequency interval between each line and the unperturbed line (which is, of course, unobservable), but the frequency interval between each line and the next one. Your final answer should take the form: "The red Balmer line splits into (???)lines. In order of increasing frequency, they come from the transitionsto (1) j =(???),toj =(???) ,(2) j =(???) to j =(???)鈥︹. The frequency spacing between line (1)and line (2)is (???) Hz, the spacing between line (2)and (3) line (???) Hzis鈥︹..鈥

Short Answer

Expert verified

The frequency spacing between lines are

6-5=0.99109eVv5-4=3.36109eV4-3=6.5109eV3-2=1.09109eV2-1=3.24109eV

Step by step solution

01

Formula Used

To findand, calculate

E=h

E=E30-E20

02

Find the wavelength

There are transition from n = 3 to n=2 ,

According to Bohr's theory:

E=E30-E20=E11n32-1n22=E119-14

where,E1=-13.6eV

then,E=-13.619-14=1.889eV

h=6.62101.61019=4.1410-15eV/sE=hvv=Eh=1.8894.1410-15=4.561014Hz

The wavelength is

=cv=31084.561014=6.5710-7m

03

Calculate fine structure

To calculate the fine structure:

Efs'=En22mc23-4nj+12

- For=2l=0,1j=12,32we have 2 -levels due to the split of n = 2,

j=12E2'=E222mc23-812+12

Where,E2=E1n2=13.64eVE2'=13.6242(2)(0.511106)3-8=5.6610-5eVj=32,E2,=E222mc23-832+12E2,=13.624220.5111063-82=1.1310-5eV

- For n=3l=0,1,2j=12,32,52we have 3-levels splitting for n =3

j=12

E3,=E322mc23-1212+12

Where,E3=E1n2=13.69eV

E3'=E1n2=13.69eVE3'=13.629220.5111063-12=-2.0110-5eVj=32

E3'=E322mc23-1232+12E3'=13.629220.5111063-6=-6.710-6eV

Forn=3l=0,1,2j=12,32,52

localid="1658383160262" j=52E3'=E322mc23-1252+12E3'=13.629220.5111063-4=2.23106eV

Then, there are six transitions of energies:

E=E30+E3'-E20+E2'=E30-E20-E3'-E2'

We need to calculateE3'+E2'E3'+E2',

TakeE=E3'+E2'

04

Calculate energy in every transition

Calculatein every transition, then:

1.

E3'=E322mc23-12j+12=E129220.5111063-12j+12E2'=E222mc23-8j+12=E124220.5111063-8j+12E4=13.6220.5111061923-12-1423-4=-3.610-5eV

2.

1232E=E3'-E2'E4=13.6220.5111061923-12-1423-4=-8.810-6eV

3.

3212E=E3'-E2'E5=13.6220.5111061923-12-1423-8=-4.9910-5eV

4.

localid="1658384765193" 3232E=E3'-E2'E2=13.6220.5111061923-6-1423-4=-4.610-6eV

5.

5212E=E3'-E2'E6=13.6220.5111061923-4-1423-8=-5.410-5eV

6.

5232E=E3'-E2'E5=13.6220.5111061923-4-1423-4=9.110-6eV

05

Calculate frequency spacing

The transition 1232has frequency less than the unperturbed line,

And the other 5-transitions have higher frequencies.

Then, the frequency spacing can be calculated as:

v6-v5=E6h-E6h=14.1410-155.410-5-4.9910-5=0.99109eV

v5-v4=E5h-E4h=14.1410-154.9910-5-3.610-5=3.36109eV

role="math" localid="1658385405705" v4-v3=E4h-E3h=14.1410-153.610-5-9.110-6=6.5109eV

v3-v2=E3h-E2h=14.1410-159.110-6-4.610-6=1.09109eV

v2-v1=E2h-E1h=14.1410-154.610-6+8.810-6=3.24109eV

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Most popular questions from this chapter

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.

Work out the matrix elements of HZ'andHfs'construct the W matrix given in the text, for n = 2.

Question: In a crystal, the electric field of neighbouring ions perturbs the energy levels of an atom. As a crude model, imagine that a hydrogen atom is surrounded by three pairs of point charges, as shown in Figure 6.15. (Spin is irrelevant to this problem, so ignore it.)

(a) Assuming that rd1,rd2,rd3show that

H'=V0+3(1x2+2y2+3z2)-(1+2+3)r2

where

i-e4蟺蔚0qidi3,andV0=2(1d12+2d22+3d32)

(b) Find the lowest-order correction to the ground state energy.

(c) Calculate the first-order corrections to the energy of the first excited states Into how many levels does this four-fold degenerate system split,

(i) in the case of cubic symmetry1=2=3;, (ii) in the case of tetragonal symmetry1=23;, (iii) in the general case of orthorhombic symmetry (all three different)?

Suppose we put a delta-function bump in the center of the infinite square well:

H'=伪未(x-a/2)

whereais a constant.

(a) Find the first-order correction to the allowed energies. Explain why the energies are not perturbed for evenn.

(b) Find the first three nonzero terms in the expansion (Equation 6.13) of the correction to the ground state,11.

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.

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