/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Q61P [Refer to Problem 4.59 for backg... [FREE SOLUTION] | 91影视

91影视

[Refer to Problem 4.59 for background.] In classical electrodynamics the potentials Aandare not uniquely determined; 47 the physical quantities are the fields, E and B.

(a) Show that the potentials

'-t,A'A+

(whereis an arbitrary real function of position and time). yield the same fields asand A. Equation 4.210 is called a gauge transformation, and the theory is said to be gauge invariant.

(b) In quantum mechanics the potentials play a more direct role, and it is of interest to know whether the theory remains gauge invariant. Show that

'eiq/

satisfies the Schr枚dinger equation (4.205) with the gauge-transformed potentials'andA', Since'differs fromonly by a phase factor, it represents the same physical state, 48and the theory is gauge invariant (see Section 10.2.3for further discussion).

Short Answer

Expert verified

(a)The potentials results in the same fields.

(b)The equation satisfies the Schr枚dinger equation withgauge invariant.

Step by step solution

01

Expression for the hamilontonia of electrodynamics and gauge transformation

The expression for hamilontonia of electrodynamics is as follows,

H=12m(p-qA)2+辩蠁

The expression for Gauge transformation is as follows,

A'=A+

The expression for gauge wave function is as follows,

'=eiq/

02

(a) Verification of the given expression

Define a new magnetic field by taking the curl of the new vector potential.

B'=A'=A+=A+=A=B

It is known that=0

Determine the new electric field by using the gradient of the new potential.

E'=-'-A't=--t-A+t=-+At-At-t=-+Xt-At-Xt=--At=E

So, t()=t.

Due to the continuity of , shift between the time-derivative and the gradient can be done.

Under gauge transformations, the electric and magnetic fields, E and B, remain invariant.

Thus, both the potentials give the same field.

03

(b) Verification of the given equation that it satisfies Schrodinger’s equation

Write the expression for the gauge transformation.

H''=12mp'-qA'2+辩蠁''=12mi-qA++q-teiq蚂/=12mi-qA+.i-q(A+)+q-teiq蚂/......(1)

Calculate the equation.

hi-qA+eiq蚂/=hi.ihqeiq蚂/+hieiq蚂/-qeiq蚂/蠄础-qeiq蚂/=qeiq蚂/+hieiq蚂/-qeiq蚂/蠄础-geiq蚂/=hieiq蚂/-qeiq蚂/蠄础

So, this can be concluded that =eiq蚂/satisfy the Schr枚dinger equation

Consider equation (1) and (2).

role="math" localid="1658223145289" H''=12mi-qA+2+q-teiq蚂/=12meiq蚂/i-qA2+q-teiq蚂/=eiq蚂/12mi-qA2+辩蠁-q-t=eiq蚂/H-qt

Evaluate the above expression further.

H''=eiq蚂/it-qt=iteiq蚂/=i't

With gauge-transformed potentials are 'andA', it is infered thatlocalid="1658218210175" '=eiq蚂/satisfies the time-dependent Schrodinger's equation.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

The (time-independent) momentum space wave function in three dimensions is defined by the natural generalization of Equation 3.54:

(p,t)=12he-ipx/h(x,t)dx(3.54).(p)1(2h)3/2e-i(p.r)Ih(r)d3r.(4.223).

(a)Find the momentum space wave function for the ground state of hydrogen (Equation 4.80). Hint: Use spherical coordinates, setting the polar axis along the direction of p. Do the 胃 integral first. Answer:

100(r,,)=1蟺补3e-r/a(4.80).(p)=1(2ah)3/21[1+ap/h2]2.(4.224).

(b) Check that (p)is normalized.

(c) Use (p)to calculate <p2>, in the ground state of hydrogen.

(d) What is the expectation value of the kinetic energy in this state? Express your answer as a multiple of E1, and check that it is consistent with the virial theorem (Equation 4.218).

<T>=-En;<V>=2En(4.218).

(a) Find the eigenvalues and eigenspinors of Sy .

(b) If you measured Syon a particle in the general state X(Equation 4.139), what values might you get, and what is the probability of each? Check that the probabilities add up to 1 . Note: a and b need not be real!

(c) If you measuredSy2 , what values might you get, and with what probabilities?

If the electron were a classical solid sphere, with radius

rc=e24O0mc2

(the so-called classical electron radius, obtained by assuming the electron's mass is attributable to energy stored in its electric field, via the Einstein formula E=mc2), and its angular momentum is (1/2)h then how fast (in m/sm/s) would a point on the "equator" be moving? Does this model make sense? (Actually, the radius of the electron is known experimentally to be much less than5.1561010m/src, but this only makes matters worse).

Use equations 4.27 4.28 and 4.32 to construct Y00,Y21Check that they are normalized and orthogonal

An electron is in the spin state

=A3i4

(a) Determine the normalization constant .

(b) Find the expectation values of Sx,Sy , and Sz.

(c) Find the "uncertainties" ,Sx , SyandSz . (Note: These sigmas are standard deviations, not Pauli matrices!)

(d) Confirm that your results are consistent with all three uncertainty principles (Equation 4.100 and its cyclic permutations - only with in place ofL, of course).

See all solutions

Recommended explanations on Physics Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.