Announcements for Physics 411 (Prof. Agashe) - Fall 2013

(1). Solutions to all HW (and midterms) are now posted here.

(2). Final exam is December 16 (Monday), 8-10 am. (Rm. 1402, i.e., usual lecture location).

(i)             It will have 6 problems (each with multiple parts).

(ii)           It is cumulative, i.e., covering the topics in all HW 2 through 12 (roughly equally divided between topics on 1st, 2nd and post 2nd exam).

(iii)          Maxwell stress tensor (from chapter 8) will not be on the final.

(iv)    A summary of relevant formulae is here.

(v)    It will be a closed book/ notes exam, but all formulae you need (except for simple mathematical results such as integral of 1 / x is log x) will be given on front page.

(no other formulae sheet will be allowed). Just to give you an idea, a sample cover page is here (note that the formulae on the actual exam could be somewhat different).

(vi)   Please bring a calculator to the exam.

(3). Some notes from review held on Friday, December 13:

(i)   The following problems were solved: HW 12.4; HW 12.1; Problem 7.17 from Griffiths; HW 8.3; Example 4.5 from Griffiths and HW 4.2.

(ii)    Please do not get confused between the full electric field (E) and coefficient in front of phase factor in its expression (i.e. E_0): for example, for a general

wave propagating in z direction (as in Eq. 9.176 from Griffiths), the full E does depend on z, but E_0 can only depend on x, y.

Of course, for a plane wave, E_0 is really a constant: see Eq. 9.43.

And, for a TEM wave in a waveguide (where E and thus E_0 has no z-component), it is the "2 (i.e., x,y)-dimensional" curl and divergence

E_0 which vanish: see equation below Eq. 9.181 or Eq. 9.195. However, the curl of full E (which has z-dependence) does not vanish (by

Faraday's law, it is negative of time derivative of magnetic field, B).

Siimilar comments for B and B_0.

For more details about the comparison between the three different types of waves that we have studied, see 1 page of note (from the review) posted here (and/or read the relevant parts of the book).

(iii)  In the formula for radiation from general dipole moment (Eq. 11.60), you are supposed to take 2nd time derivative of dipole moment vector, then take its magnitude (and not the “other way around”,

i.e.,it is not the 2nd time derivative of magnitude).

For example, in HW 12.4, i.e., problem 11.9 from 3rd edition (-> 11.10 from 4th edition) of Griffiths, the magnitude of dipole moment of (spinning)

ring of charge is constant in time (i.e., it's time derivative is zero), but direction is not and so there is power radiated.

(I am sorry that did not get time to finish this problem during the review, but you can see look up posted solution for more details.)

(4). Course evaluations are due here by Sunday, December 15.

(5). 2nd midterm exam statistics are as follows:

average: 31.3 (out of 41); "standard deviation": 7.8; maximum score obtained: 41; minimum: 18.5...

(6). 1st midterm exam statistics are as follows:

average: 32 (out of 50)