Homework 2 solutions

are here. I'll add Quiz 2 & 3 solutions tonight or this weekend.

HW3 is out

you can find it here. Due Monday in the lab period.

Solutions and such

I have solutions for quiz 1 and homework 1. You'll get your graded HW1 back tomorrow (Wed), I suspect the TAs will have the quizzes back to you shortly as well. 

HW2 is out

and you can find it here. Due at the end of Wednesday's lab period.

HW hints

For the first problem:

1. http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/polebarn.html
2. http://en.wikipedia.org/wiki/Ladder_paradox
3. http://www.xs4all.nl/~johanw/PhysFAQ/Relativity/SR/barn_pole.html

For the second problem, the length must be contracted according to the astronaut. The astronaut would report a velocity which is the contracted distance divided by the time he or she measured.

For the third problem, the proton sees a contracted length. It would observe a time consistent with this distance divided by the relative velocity, whereas in the laboratory we would observe a time which is the rest length of the tube divided by velocity.

For the last problem, the difference between dilated and proper time is 2s every 86400s. This must mean that the spaceship clock runs a factor (1+2/86400) slow.

Homework 1

is out. Due at the end of the lab period Monday (so you can ask me or the TAs questions in lab ...)

The first problem is tricky. Discussions of it are easy to find online, we will go over it in lecture on Monday a bit.

Today's lab

We'll measure Planck's constant.

The optics HW is extended until tomorrow night.

Homework problem 2

Think of a toroidal solenoid as a cylindrical solenoid wrapped back on itself. A toroid is basically a donut. If you cut it at one point and straightened it out, it would be a regular old solenoid of length l=2πr, the inductance would be L=µN^2A/l, and the energy U=(1/2)LI^2.

The figure they provide is terrible ... look at this one.

Today's lab

Today, we'll do two little experiments on mirrors & snell's law, and one on lenses:

http://faculty.mint.ua.edu/~pleclair/ph102/Labs/reflection_refraction/reflection_refraction.pdf
http://faculty.mint.ua.edu/~pleclair/ph102/Labs/lenses/lenses.pdf

Even though there are three experiments, overall it is still very fast and should not take the whole period.

In other news, the tests should be graded tomorrow. I will also extend the current HW deadline since I was out, but the next one will come out tonight (due Sun).

New HW out

Due Thursday at midnight, induction/ac circuits/em waves.

The next homework after that will likely be due Saturday or Sunday. 

Short homework on magnetism out ...

due Friday night. Should not be too bad, we'll go over many of them on Friday.

Eating candy off of the ground

Using equations at random is like eating candy off of the ground.

HW3 is out

All about circuits; due next Tuesday at midnight.

HW2 #7

Q1: On problem 7 (Moving a Charge) of the second homework set I keep getting this error message when I input my answer in a variety of different ways: "There is an error in your submission. Make sure you have formatted it properly."

Q2: I'm sure I have problem 7 right, but it is being marked wrong.

I've gotten these questions many times already, and in almost every case you did have the right answer. For some reason this problem is weirdly particular about the order the operations (superscript, subscript, square root) are put in.

If you definitely have the right answer, and can prove it (screen shot, copy & paste, etc), show me and I'll just go in and override your score for that question to give you full credit.

If this happens more than (roughly) 20 times, I will decide it is not worth the effort anymore and will give everyone full credit on #7 :-)

Relativity HW extended

I'll push the deadline for the relativity HW until Friday so you can worry about the test more efficiently.

This will not affect the HW2 deadline, nor the occurrence of HW3 shortly thereafter.

(This is for Dr. LeClair's section only. Dr. Mazumdar may or may not decide to do the same.)

HW2 is out

Your second homework set is out (LeClair's section), due Wednesday at midnight. It is a bit longer than the first, but meant to double as study material for Thursday's exam. More details on that later, however ... for now, suffice it to say that you should not delay in starting the second homework.

There is likely to be a shorter homework due on Friday covering current & dc circuits.

MasteringPhysics

If you have not been able to register for MasteringPhysics, it is because the existing code has been used too many times. If this is the case, email me and I will give you a new code.

If you're already signed up for MasteringPhysics for my or Dipanjan's PH102 section, you don't need to do anything. This is just if you haven't been able to sign up.

HW1 is out

For Dr. LeClair's section: your first HW (on relativity) is out on MasteringPhysics now, due Monday at midnight. We'll go over some of the questions in class on Monday.

Last homework

Here you go. It is due at the start of the final exam.

This homework is just a small review of sorts, with a little stronger emphasis on recent things. They are good practice questions for the final, one or two might even show up in nearly the same form on the final.

(Of course, this small homework set does not cover all the material. More practice problems will be posted tonight that cover most of the remaining material.)

Exam 2 / HW 7

Here is yesterday's exam. I will have them graded by Monday, possibly with grades on moodle over the weekend. I'll post here when they are ready.

Your next homework (#7) is to do the remaining two exam problems you didn't choose yesterday. Due tonight by midnight, but we'll go over the problems quickly in class today.