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a) Compute x, p, x2, p2, for the states 0and1 , by explicit integration. Comment; In this and other problems involving the harmonic oscillator it simplifies matters if you introduce the variable 尘蝇xand the constant (尘蝇)14.

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?

Short Answer

Expert verified

(a) The value of x is x||2dx=0 and the value of p is role="math" localid="1658998623381" mdxdt=0 and The value of x2 is 32m andP2 is 3m2.

(b)The uncertainty principal for these states is greater than 2.

(c) The value of the average kinetic energy is role="math" localid="1658998806318" 34(n=1)14(n=0) and The average potential energy is 34(n=1)14(n=0).The sum of these two is same as expected value.

Step by step solution

01

Define explicit integration

In this method, the accelerations and velocities at a specific time point are taken to be constant during a time interval and are utilised to find the location of the following time point.

02

:The value of ⟨x⟩ and  ⟨p⟩

(a)

The function 0 is even, and 1is odd. In either case ||2is even, so the value of x=x||2dx=0. Therefore p=mdxdt=0

Thus, the value of x is x||2dx=0 and the value of pismdxdt=0.

Now, evaluate the value of x2and p2.

The below values are known that

0=伪别221=2伪尉别22

For n=0, the value of x2 will be

x2=2x2e2/2dx ...(1)

For given equation-

尘蝇xx=尘蝇x2=2(尘蝇)

And

x=尘蝇dx=诲尉尘蝇

Substitute the value of x2 and dx in equation (1).

x2=22尘蝇e2/2诲尉尘蝇x2=2尘蝇3/22e2诲尉=1尘蝇2=2尘蝇

And the value of P2 is

P2=0iddx20dx=22尘蝇e2/2d2诲尉2e2/2诲尉=m2=m2

For n=1, the value of x2will be

x2=22x22e2dx

Substitute the value of x2 and dx in the above equation. So,

x2=22尘蝇3/24e2诲尉=32尘蝇4=32尘蝇

And the value of P2 is

P2=222me2/2d2d2(e2/2)d=2m3432)=3m2

Therefore, the value of x2is 32m andP2 is3m2 .

03

The uncertainty principal of above states

(b)

The value of x will be for n=0:

x=x2)x2=2尘蝇p=p2p2=尘蝇2xp=2尘蝇尘蝇2=2(Rightattheuncertaintymoment)

For n=1, the value will be :

x=32尘蝇p=3尘蝇2xp=32>2

The uncertainty principal for these states is greater than 2.

04

The value of the average kinetic energy and the average potential energy 

c)

The average kinetic energy is:

T=12mP2=34(n=1)14(n=0)

The average potential energy is

V=12m2x2=34(n=1)14(n=0)

T+V=H=32(n=1)=E112(n=0)=E0 , as expected.

So, the value of the average kinetic energy is 34(n=1)14(n=0) and the average potential energy is 34(n=1)14(n=0).The sum of these two is same as expected value.

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Most popular questions from this chapter

Consider the double delta-function potentialV(x)=-[x+a+x-a]Whereand are positive constants

(a) Sketch this potential.

(b) How many bound states does it possess? Find the allowed energies, for=/maand for=2/4ma, and sketch the wave functions.

What is the Fourier transform (x) ? Using Plancherel鈥檚 theorem shows that(x)=12eikxdk.

A particle of mass m in the infinite square well (of width a) starts out in the left half of the well, and is (at t=0) equally likely to be found at any point in that region

(a) What is its initial wave function, (x,0)? (Assume it is real. Don鈥檛 forget to normalize it.)

(b) What is the probability that a measurement of the energy would yield the values2h22ma2?

a) Construct 2(x)

b) Sketch 0,1and2

c) Check the orthogonality of012 by explicit integration.

Hint:If you exploit the even-ness and odd-ness of the functions, there is really only one integral left to do.

This problem is designed to guide you through a 鈥減roof鈥 of Plancherel鈥檚 theorem, by starting with the theory of ordinary Fourier series on a finite interval, and allowing that interval to expand to infinity.

(a) Dirichlet鈥檚 theorem says that 鈥渁ny鈥 function f(x) on the interval [-a,+a]can be expanded as a Fourier series:

f(x)=n=0[ansin苍蟺虫a+bncos苍蟺虫a]

Show that this can be written equivalently as

f(x)=n=-cnei苍蟺虫/a.

What is cn, in terms of anand bn?

(b) Show (by appropriate modification of Fourier鈥檚 trick) that

cn=12a-a+af(x)e-i苍蟺虫/adx

(c) Eliminate n and cnin favor of the new variables k=(苍蟿蟿/a)andF(k)=2/acn. Show that (a) and (b) now become

f(x)=12n=-F(k)eikxk;F(k)=12-a+af(x).eikxdx.

where kis the increment in k from one n to the next.

(d) Take the limit ato obtain Plancherel鈥檚 theorem. Comment: In view of their quite different origins, it is surprising (and delightful) that the two formulas鈥攐ne for F(k) in terms of f(x), the other for f(x) terms of F(k) 鈥攈ave such a similar structure in the limit a.

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