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A particle of mass m is in the potential

V(x)={,(x<0)-32h2ma2,(0xa)0,(x>a)

How many bound states are there?

In the highest-energy bound state, what is the probability that the particle would be found outside the well (x>a)? Answer: 0.542, so even though it is 鈥渂ound鈥 by the well, it is more likely to be found outside than inside!

Short Answer

Expert verified
  1. Three
  2. p3=0.54204

Step by step solution

01

Solving the Schrodinger equations

The given potential is the hybrid of the finite and infinite square wells is:

V(x)={,(x<0)-32h2ma2,(0xa)0,(x>a)

In the second region,

-h22m"-32h2ma2=E"=-l2

Where,

l=2mh2E+32h2ma2inthethirdregion,-h22m"=E"=kWhere,k=-2mEh2Hence,thesolutionsare,x=0,x<0Acoslx+Bsinlx,0xaCe-kx,x>a

02

Finding the constants

From the continuity of wave functions

Atx=00=0A=0Atx=aBsinla=Ce-ka

03

Finding the bound states

Dividing both the equations,

tanla=-lkLetz=la,then:z0=ah2m32h2ma2l2+k2h2=2m32h2ma2l2+k2h2=haz0z02=l2+k2a2z02=z2+k2a2ka=z02-z2ka=64-z2since,tanla=-lktanz=-lakatanz=--164/z2-1Thisisatranscendentalequation.Itcanbesolvedgraphicallyornumerically.Hence,wecanconcludethattherearethreeboundstates.z1=2.98165165z2=5.53899816z3=7.95732149

04

Calculating the probability for the particle to be found outside the wellb)

Since, the energy is given by

x=0,x<0Bsinlx,0xasinlae-kaBe-kx,x>a

Hence, the probability over its entire range from to for the second line in this equation, and from x=ato x=for the third line in this equation is:

localid="1658226702587" 0asin2lxdx+sin2lae-2kaae-2kxdxB2

Therefore, the probability of the particle being outside the box,

p3=B2sin2lae-2kaae-2kxdx0asin2lxdx+sin2lae-2kaae-2kxdxB2

Calculating the above integral, we get,

ae-2kxdx=e-2ak2k0asin2lxdx=-sin2al-2al4l

Hence, substituting these values in the probability equation:

p3=sin2la2k-sin2al-2al4l+sin2la2kp3=sin2z264-z2-sin2z-2z4z+sin2z264-z2Substitudez3=7.95732149,andweget,p3=0.54204

Therefore, the probability is 0.54204the particle being outside the box,

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Most popular questions from this chapter

Calculate (x),(x2),(p),(p2),xandp,for the nth stationary state of the infinite square well. Check that the uncertainty principle is satisfied. Which state comes closest to the uncertainty limit?

Show that E must be exceed the minimum value of V(x) ,for every normalizable solution to the time independent Schrodinger equation what is classical analog to this statement?

d2dx2=2mh2[V(x)E];

IfE<Vmin then and its second derivative always have the same sign. Is it normalized?

Derive Equations 2.167 and 2.168.Use Equations 2.165 and 2.166 to solve C and D in terms of F:

C=(sin(la)+iklcos(la))eikaF;D=(cos(la)iklsin(la))eikaF

Plug these back into Equations 2.163 and 2.164. Obtain the transmission coefficient and confirm the equation 2.169

a) Compute x,p,x2,p2, for the states 0and 1, by explicit integration. Comment; In this and other problems involving the harmonic oscillator it simplifies matters if you introduce the variable mxand the constant (m)1/4.

b) Check the uncertainty principle for these states.

c) Compute T(the average kinetic energy) and V(the average potential energy) for these states. (No new integration allowed). Is their sum what you would expect?

The Dirac delta function can be bought off as the limiting case of a rectangle area 1, as the height goes to infinity and the width goes to Zero. Show that the delta function well (Equation 2.114) is weak potential (even though it is infinitely deep), in the sense that Z00. Determine the bound state energy for the delta function potential, by treating it as the limit of a finite square well. Check that your answer is consistent with equation 2.129. Also, show that equation 2.169 reduces to Equation 2.141 in the appropriate limit.

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