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 1^{st}, 2^{nd}
and post 2^{nd} 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)