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A particle of mass m is in the state:

(x,t)=Aea[(mx2/h)+it]

where A and a are positive real constants.

(a) Find A.

(b) For what potential energy function, V(x), is this a solution to the Schr枚dinger equation?

(c) Calculate the expectation values of x,x2 , p, andp2 .

(d) Find 蟽x and 蟽p. Is their product consistent with the uncertainty principle?

Short Answer

Expert verified

a. A=2amh1/4

b.V(x,t)=2ma2x2

c. x=0, x2=h4am, p=0,p2=ham

d. Yes, it鈥檚 consistent with the uncertainty principle

Step by step solution

01

Normalizing the wave equation (a)

Calculating for A by normalizing the wave function.

1=|(x,t)|2dx1=*(x,t)(x,t)dx1=(Aea[(mx2/h)+it])(Aea[(mx2/h)it])dx1=A2e2amx2/hdx

Further solving above equation,

1=2A20ex2/[h/(2am)]2dx1=2A2.h/2am21=A2蟺丑2amA2=2amh1/2A=2amh1/4

Thus, the value of A is 2amh1/4.

02

Finding the potential energy for which it is a solution of the Schrödinger equation (b)

Schrodinger equation is given by,

t=ih2m2x2ihV(x,t)(x,t)

Solving for V(x,t),

V(x,t)=hi1(x,t)ih2m2x2tV(x,t)=hi2amh1/4ea[(mx2/h)+it]ih2m2amh1/42x2(ea[(mx2/h)+it])2amh1/4(ea[(mx2/h)+it])(ia)V(x,t)=hea[(mx2/h)+it]ih2m2x2(ea[(mx2/h)+it])aea[(mx2/h)+it]V(x,t)=hea[(mx2/h)+it]ih2m2amh12amhx2ea[(mx2/h)+it]+aea[(mx2/h)+it]

Further solving above equation,

V(x,t)=ha2amhx21+aV(x,t)=2ma2x2

Thus, the potential energy function isV(x,t)=2ma2x2 .

03

Calculating the expectation values of x (c)

Solving for the expectation values.

x=x|(x,t)|2dx|(x,t)|2dxx=虫蠄*(x,t)(x,t)dxx=x2amh1/4ea[(mx2/h)+it]2amh1/4ea[(mx2/h)it]dxx=2amhxe2amx2/hdx

Since, integral of an odd function over a symmetric interval is zero.

Therefore, the expectation value is zero x=0.

Now, for x2

x2=x2|(x,t)|2dx|(x,t)|2dxx2=x2(x,t)*(x,t)dxx2=x22amh1/4ea[(mx2/h)+it]2amh1/4ea[(mx2/h)it]dxx2=2amhx2e2max2/hdx

x2=22amh0x2ex2/[h/(2am)]2dxx2=22amh.2!1h/2am23x2=h4am

Therefore, the value of x2 is h4am.

04

Calculating the expectation values for p (c)

Using the Ehrenfest鈥檚 theorem,

p=mvp=mdxdt

Since x=0.

Therefore, the value of p is zero.

Now, solving for p2.

p2=*(x,t)ihx2(x,t)dxp2=h2*(x,t)2x2dxp2=h22amh1/4ea[(mx2/h)it]2x22amh1/4ea[(mx2/h)+it]dx

Further solving above equation,

p2=h22amh2amh12amhx2e2amx2/hdxp2=h22amh2amhe2amx2/hdx2amhx2e2amx2/hdxp2=h22amh4amh0ex2/[h/2am]2dx2amh0x2ex2/[h/2am]2dxp2=h22amh4amhh/2am22amh2!1!h/2am23

Further solving above equation,

p2=h24amh1214p2=ham

Therefore, the value of p2 is ham.

05

Checking the consistency with Heisenberg Uncertainty Principle

The standard variation of an observable gives the uncertainty, hence,

x=螖虫螖虫=x2x2螖虫=h4am0螖虫=12ham

The calculation of standard deviation p is,

p=螖辫螖辫=p2p2螖辫=ham0螖辫=ham

The uncertainty can be written as,

螖虫螖辫=12hamham螖虫螖辫=h2

And Heisenberg Uncertainty Principle states that

螖虫螖辫h2

Therefore, it is consistent with the Heisenberg Uncertainty Principle.

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