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Question: Consider a cubic 3D infinite well of side length of L. There are 15 identical particles of mass m in the well, but for whatever reason, no more than two particles can have the same wave function. (a) What is the lowest possible total energy? (b) In this minimum total energy state, at what point(s) would the highest energy particle most likely be found? (Knowing no more than its energy, the highest energy particle might be in any of multiple wave functions open to it and with equal probability.)

Short Answer

Expert verified

Answer

(a) The lowest possible total energy is 1072h22mL2.

(b) The highest energy particle is most likely to found at the centre of the well.

Step by step solution

01

Identification of given data

The side length of 3D well is L.

The number of identical particles is n = 15 .

The mass of the identical particles is m.

The lowest energy wave function has nx,ny,nz=1,1,1. The next two lowest have (2,1,1), (1,2,1) and (1,1,2) . By combining each from these two there will six pairs for adding in existing two. Next higher will be (2,2,1) ,(2,1,2) and (1,2,2). This adds six to existing eight states. The fifteenth state is(3,1,1) ,(1,3,1) and (1,1,3) . for the last particle

02

Step 2(a): Determination of lowest possible total energy

The lowest possible total energy is given as:

Et=nx2+ny2+nz22h22mL2

Here, h is the Planck鈥檚 constant.

Substitute all the values in the above equation.

Et=212+12+12+622+12+12+622+22+12+32+12+122h22mL2\hfillEt=1072h22mL2

Therefore, the lowest possible total energy is 1072h22mL2.

03

Step 3(b): Determination of point for highest energy particles

Two among the three quantum numbers are unity, which gives maximum wave function at the centre of 3D well. The other quantum number is three for which there will be three maxima. This indicates that particle is most likely found at three points. The probability of finding particle is at the centre of the 3D well.

Therefore, the highest energy particle is most likely to found at the centre of the well.

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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?

An electron in a hydrogen atom is in the (n,l,ml) = (2,1,0) state.

(a) Calculate the probability that it would be found within 60 degrees of z-axis, irrespective of radius.

(b) Calculate the probability that it would be found between r = 2a0 and r = 6a0, irrespective of angle.

(c) What is the probability that it would be found within 60 degrees of the z-axis and between r = 2a0 and r = 6a0?

A mathematical solution of the azimuthal equation (7-22) is ()=Ae-顿蠁+Be-顿蠁 , which applies when D is negative, (a) Show that this simply cannot meet itself smoothly when it finishes a round trip about the z-axis. The simplest approach is to consider =0 and =2. (b) If D were 0, equation (7-22) would say simply that the second derivative ()of is 0. Argue than this too leads to physically unacceptable solution, except in the special case of () being constant, which is covered by the ml=0 , case of solutions (7-24).

(a) What is the expectation value of the distance from the proton of an electron in a 3p state? (b) How does this compare with the expectation value in the 3 d state, calculated in Example 7.7? Discuss any differences.

A comet of 1014kg mass describes a very elliptical orbit about a star of mass31030kg , with its minimum orbit radius, known as perihelion, being role="math" localid="1660116418480" 1011m and its maximum, or aphelion, 100 times as far. When at these minimum and maximum

radii, its radius is, of course, not changing, so its radial kinetic energy is 0, and its kinetic energy is entirely rotational. From classical mechanics, rotational energy is given by L22I, where Iis the moment of inertia, which for a 鈥減oint comet鈥 is simply mr2.

(a) The comet鈥檚 speed at perihelion is6.2945104m/s . Calculate its angular momentum.

(b) Verify that the sum of the gravitational potential energy and rotational energy are equal at perihelion and aphelion. (Remember: Angular momentum is conserved.)

(c) Calculate the sum of the gravitational potential energy and rotational energy when the orbit radius is 50 times perihelion. How do you reconcile your answer with energy conservation?

(d) If the comet had the same total energy but described a circular orbit, at what radius would it orbit, and how would its angular momentum compare with the value of part (a)?

(e) Relate your observations to the division of kinetic energy in hydrogen electron orbits of the same nbut different I.

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