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Consider the Gaussian distribution

(x)=Ae(xa)2

where A, a, and 位 are positive real constants. (Look up any integrals you need.)

(a) Use Equation 1.16 to determine A.

(b) Find銆坸銆,銆坸2銆,and 蟽.

(c) Sketch the graph of 蚁(x).

Short Answer

Expert verified

a. A=

b. x=a, x2=12+a2, =12

c. Graph is shown in figure (1).

Step by step solution

01

Step 1:

The required integrals are given by:

0x2nex2/a2dx=(2n)!n!(a2)2n+1......(1)0x2n+1ex2/a2dx=n!2a2n+2......(2)

The given Gaussian probability distribution is assumed to be valid over the whole line

i.e.

(x)=Ae(xa)2 x

02

Normalizing the distribution and finding A (a)

Calculating for A by normalizing the function,

(x)dx=1Ae(xa)2dx=1

Assuming, y=xa

Hence, the equation becomes

Ae位测2dy=1

Aey2(1/)2dy=1

This integral can be taken from 0to, multiplying with a factor 2, since it鈥檚 an even function of y.

2A0ey2(1/)2dy=1

Now, from equation 1, putting n=0

2A(1/2)=12A=2A=

Thus, the value of A is .

Hence, the Normalised probability distribution comes out to be

(x)=e(xa)2 x

03

Solving for x2  and ⟨x⟩2   (b)

First, we solve for x2

role="math" localid="1655379313238" x=x蚁(x)dx(x)dxx=xe(xa)2dx1x=(y+a)e位测2dyx=(ye位测2dy+ae位测2dy)

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

i.e. ye位测2dy=0

Therefore,

x=2a0ey2(1/)2dyx=2a.(1/)2x=.a.x=a

Thus, value of x is a.

Now, for x2

x2=x2(x)dx(x)dxx2=x2e(xa)2dx1x2=(y+a)2e位测2dyx2=y2e位测2dy+2aye位测2dy+a2e位测2dyx2=20y2ey2(1/)2dy+2a20ey2(1/)2dyx2=2.2!1!1/23+2a2.1/2x2=123+a2x2=12+a2

Thus, value of x2 is 12+a2.

04

Finding the standard deviation (b)

The standard deviation can be calculated as,

=x2x2=(12+a2)a2=12

Thus, value of 蟽 is 12.

05

Graph for ρ(x).

Figure (1)

Here,

(x)=e(xa)2=1a=1

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Most popular questions from this chapter

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?

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In general, quantum mechanics is relevant when the de Broglie wavelength of the principle in question(h/p)is greater than the characteristic Size of the system (d). in thermal equilibrium at (kelvin) TemperatureTthe average kinetic energy of a particle is

p22m=32kBT

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The purpose of this problem is to anticipate which systems will have to be treated quantum mechanically, and which can safely be described classically.

(a) Solids. The lattice spacing in a typical solid is around d=0.3nm. Find the temperature below which the free 18electrons in a solid are quantum mechanical. Below what temperature are the nuclei in a solid quantum mechanical? (Use sodium as a typical case.) Moral: The free electrons in a solid are always quantum mechanical; the nuclei are almost never quantum mechanical. The same goes for liquids (for which the interatonic spacing is roughly the same), with the exception of helium below 4K.

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The needle on a broken car speedometer is free to swing, and bounces perfectly off the pins at either end, so that if you give it a flick it is equally likely to come to rest at any angle between 0 tox.

  1. What is the probability density? Hint: ()d is the probability that the needle will come to rest between and+d .
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At time t = 0 a particle is represented by the wave function

(x,0)={A(x,0),0xa,A(bx)/(ba),axb,0,otherwise,where A, a, and b are (positive) constants.

(a) Normalize (that is, find A, in terms of a and b).

(b) Sketch (x,0), as a function of x.

(c) Where is the particle most likely to be found, at t = 0?.

(d) What is the probability of finding the particle to the left of a? Check your result in the limiting cases b = a and b= 2a.

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