HW6 Solutions

Here.

Einstein on induction

Here's what Einstein had to say about magnetic induction:

Imagine a conducting loop moving relative to a magnet as seen by two different observers: one on the magnet the other on the loop. Both observers see the identical EMF generated in the coil using the flux form of Faraday's law, but explain the result using two different reasons. The observer on the magnet sees the magnet as stationary with an unchanging magnetic field, while the conducting loop moves. All of the charges within the loop move with the loop, and due to the B-field experience a sideways Lorentz force, which generates the EMF. On the other hand, an observer on the loop sees a changing magnetic field due to a moving magnet (relative to the loop's reference frame) and no Lorentz force (charges in the loop are not moving). This changing magnetic field means ΔB / Δ t ≠ 0, which creates an electric field that generates the current.

This is what I was trying, less eloquently, to explain this morning.

Quizlet tomorrow

A good hint would be to look at "Example 20.4" and "Applying Physics 20.2" in the text, the sliding bar problem (Motional EMF).

The notes also discuss the same basic problem, e.g., pg 174. Or, look at problems 6 & 7 here.

Whatever I come up with for the quiz will be related to launching metal bars off of conducting rails in some way. Possibly at enormous velocities.

Homework 5 solutions

Here you go.

dc/rc lab reports

If you picked up your graded dc/rc lab reports either today or yesterday: you picked them up off of a pile that was not meant for you (yet). I didn't have them recorded in the gradebook yet -- you grabbed them off of the pile the TAs left for me.

So. If you already have a dc/rc lab report, you'll want to bring it back to me right away ...

I never could get the hang of Thursdays.

Thursday, we'll do a lab on mutual inductance. That is, we'll build a small transformer. We'll cover the material relevant to this lab in Thursday morning's lecture on inductance.

Other things:

I hope to have all solutions (quiz, exam, homework) up to date by the weekend, I will try to put out at least an answer key for everything by Thursday afternoon.

In the lab (and probably the lecture too) we'll go over remaining questions on HW6, which is due by the end of Thursday.

We'll finish most of induction Thursday itself, and will probably only need 1 day for ac circuits. We might actually be ahead of schedule by the end of Monday. If this actually happens, I'll probably devote one day (or maybe a half day) next week to a 'special topics' lecture, e.g., how do hard disks/computer memories work. Other suggestions for a special topic? Drop a comment.

eLearning FAIL

Right. By default, eLearning chooses not to show you any new grades until I explicitly tell it to release them for student view. Basically, this means that my upload earlier today did not show up for you.

I think it is fixed now, and you should be able to see all of your grades.

Wednesday's lab

Today, we'll measure the earth's magnetic field.

Or, depending on how careful you are, perhaps you'll measure the remnant field of the ferrous I-beams in the building, or the steel leg holding up your table. :-)

NOAA gives you a way to check your answer. Beware, imminent data overload ...

Grades / eLearning

Just uploaded current grades into eLearning. This includes:

• Quizzes 1-5*
• Homework 1-4
• Labs 1-4
• Exam 1
• Current average grade**

When you get a chance, make sure it looks right ...

* Quiz 4 was a 'free quiz' - dropped for free, unless you scored higher it than your lowest quiz score otherwise. In which case, Quiz 4 replaces what was previously your lowest grade ...
** This is a worst-case scenario - no dropped HW, Lab, or Quiz grades, excepting the case discussed in the previous footnote. Weighting of various components is according to the syllabus.

HW 6 is out

Right here. Not due until Thursday, we'll set most of them up in Wednesday's lecture & lab.

HW 4 solutions

Here you are.

Lab for Mon 20 Jul 09

Monday, we'll do a lab investigating series & parallel combinations of resistors and resistor-capacitor combinations.

Here's the procedure.

Homework 5

Here you are, due Tuesday night. Relatively short ...

HW 3 Solutions / Quiz 5

Here are solutions to HW3.

Tomorrow's short quiz will be on dc circuits, covering material from this past Friday. It won't be too bad.