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Exercise 80 discusses the idea of reduced mass. When two objects move under the influence of their mutual force alone, we can treat the relative motion as a one particle system of mass =m1v2/(m1+m2). Among other things, this allows us to account for the fact that the nucleus in a hydrogen like atom isn鈥檛 perfectly stationary, but in fact also orbits the centre of mass. Suppose that due to Coulomb attraction, an object of mass m2and charge -eorbits an object of mass m1 and charge +Ze . By appropriate substitution into formulas given in the chapter, show that (a) the allowed energies are Z2mE1n2, where is the hydrogen ground state, and (b) the 鈥淏ohr Radius鈥 for this system is m锄渭a0 ,where a0is the hydrogen Bohr radius.

Short Answer

Expert verified

(a) The allowed energies are isZ2mE1n2.

(b) The Bohr鈥檚 Radius is m窜渭a0.

Step by step solution

01

Formula used:

From Section 7.8, you know that, all formulas for hydrogen apply to hydrogen like atoms if you simply replace e2toZe2.

Hence,

Energy levels of hydrogen like atoms, En=m(Ze2)22(4蟺蔚0)2h2n21n2 鈥︹赌︹赌︹赌(1)

Where, z is the atomic mass, h is Plank鈥檚 constant, n = principal quantum number,0is the permittivity of free space.

And the Bohr鈥檚 Radius is,

rn=n2(4蟺蔚0)h2m(ze2) 鈥.. (2)

Where, m is the mass.

02

Finding Energy levels:

Now, using eq. (1) and replacing mass (m) with Effective mass , you get,

En=mZe2224蟺蔚02h21n2=Z2m-me424蟺蔚02h21n2=Z2mE1n2

Hence, the allowed energies are Z2mE1n2.

Where, E1is the Energy of hydrogen ground state.

03

Finding the Bohr’s Radius:

Again, using eq. (2) and replacing mass (m) with Effective mass , you get,

rn=124蟺蔚0h2Ze2=m4蟺蔚0h2窜渭me2=m窜渭a0

Hence, the Bohr鈥檚 Radius is m窜渭a0.

Where, a0is the hydrogen Bohr radius.

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Most popular questions from this chapter

For the more circular orbits, =n-1and

P(r)r2ne-2r/na0

a) Show that the coefficient that normalizes this probability is

localid="1660047077408" (2na0)2n+11(2n)!

b) Show that the expectation value of the radius is given by

r=n(n+12)a0

and the uncertainty by

r=na0n2+14

c) What happens to the ratior/rin the limit of large n? Is this large-n limit what would be expected classically?

In general, we might say that the wavelengths allowed a bound particle are those of a typical standing wave,=2L/n , where is the length of its home. Given that =h/p, we would have p=nh/2L, and the kinetic energy, p2/2m, would thus be n2h2/8mL2. These are actually the correct infinite well energies, for the argumentis perfectly valid when the potential energy is 0 (inside the well) and is strictly constant. But it is a pretty good guide to how the energies should go in other cases. The length allowed the wave should be roughly the region classically allowed to the particle, which depends on the 鈥渉eight鈥 of the total energy E relative to the potential energy (cf. Figure 4). The 鈥渨all鈥 is the classical turning point, where there is nokinetic energy left: E=U. Treating it as essentially a one-dimensional (radial) problem, apply these arguments to the hydrogen atom potential energy (10). Find the location of the classical turning point in terms of E , use twice this distance for (the electron can be on both on sides of the origin), and from this obtain an expression for the expected average kinetic energies in terms of E . For the average potential, use its value at half the distance from the origin to the turning point, again in terms of . Then write out the expected average total energy and solve for E . What do you obtain

for the quantized energies?

A hydrogen atom electron is in a 2p state. If no experiment has been done to establish a z-component of angular momentum, the atom is equally likely to be found with any allowed value of LZ. Show that if the probability densities for these different possible states are added (with equal weighting), the result is independent of both and

An electron is trapped in a quantum dot, in which it is continued to a very small region in all three dimensions, If the lowest energy transition is to produce a photon of 450nm wavelength, what should be the width of the well (assumed cubic)?

For an electron in the(n,l,ml)=(2,0,0) state in a hydrogen atom, (a) write the solution of the time-independent Schrodinger equation,

(b) verify explicitly that it is a solution with the expected angular momentum and energy.

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