MIT circuits notes & more

Some nice slides & notes from MIT's intro electronics course. Might be good reference material for our upcoming mid-semester project.

Notes on electric forces and fields

My notes for the non-calculus class (PH102) may be handy from time to time. The next several day's material corresponds to Ch. 2-3 in the notes.

(warning, ~23Mb PDF file)

Friday's class

Friday, we'll be starting to discuss electric forces and fields. We'll skip most of the beginning of chapter 21 in your text, since it is fairly descriptive stuff you can easily read about, and dive right in to calculating electric forces. This would be the last few sections of Ch. 21, and the beginning of Ch. 22. I'll go over some questions on the HW set as well.

If you're having trouble remembering some of the vector manipulation, I did write a short math guide some time ago (and never quite finished, but close). Hopefully the quick tour of vectors on Wednesday didn't scare too many of you away ... we will start out slowly and work our way up to the harder things.

For Monday, you should have already read Ch. 21 and 22 (or skimmed them at least, let's be realistic here).

What we covered today / what comes next

Today, what I basically derived was the Drude model of conductivity (or from an alternate viewpoint, the complex dielectric function). Griffiths covers essentially the same material in Ch. 9, treating the problem from a dielectric-centric viewpoint. The Feynman Lectures (vol II) also does a great job of covering the same material, in much the same way that we started today (i.e., from harmonically-oscillating charges). I would suggest reading Feynman, then Griffiths if you are curious. Follow that with Jackson Ch. 7 (link below) if you're really excited.

Here are a couple links you might find useful, if you are interested in going through what we did today a less brutal pace:

• Summary of the Drude model
• Ch. 1 of Solymar & Walsh does an excellent intro job (awesome book,I have a copy)
• Jackson Ch. 7 is fairly readable (when compared to the bulk of the book ...)
• Feynman Lectures II.32 (must read; dielectric-centric)
• Brief Derivation (fast-paced, but good)

Anyway: now we know why metals are shiny, and insulators are mostly transparent.

This brings up a question: we have one more recitation (Fri) which will be devoted to the RFID project, and one more lecture (Mon). What do you want to hear for your last lecture in PH126?

Anything you want, within reason and physics-related (if tangentially), I'll do my best. Leave your suggestions in the comments.

Exam III

As you are probably aware, exam III is this Friday. There will be five problems, you must solve any two. The topics are

• ac circuits
• relativity
• induction
• Maxwell's equations / EM waves

Obviously, one of these sections will have two problems, the others a single problem. Here's what you might want to study/reread before the exam:

• ac circuits - my PH102 notes
• relativity - PH102 notes, Griffiths 12.1 (all) and 12.3.1-2
• induction - PH102 notes, Griffiths 7.2
• Maxwell - Griffiths 7.3, 8.1, 9.2.1

The corresponding example problems in Griffiths and end-of-chapter problems in my PH102 notes are particularly worth reading through.

This is assuming that you have already read the relevant homework solutions on these topics, which are also helpful. The exam problems will not be as difficult as the usual homework problems, however.

Relativity

If you find relativity interesting, and you've had a bit of math, you'll probably find these lecture notes very nice. In fact, they've been turned into a book by Prof. Carroll, which has been well-received (it is what we use for our grad relativity course).

There is also a "non-nonsense" introduction to general relativity, the first bits of which should be familiar. Don't be scared by the tensors later on, the barrier is mostly the notation.

Anyway: good book, free preview online. Can't beat that.

Friday's recitation

Tomorrow, we'll consider some of the microscopic physics behind conduction in metals, which will lead us to the general version Ohm's law among other things. I will have a handout in some form for this, since I'd like to do a bit more than is in the textbook.

In the remaining time (I hope our discussion will take about 30-35min ...) we'll go over the homework problems due on Friday.

Also: next week we'll start magnetism, so please read sections 5.1 and 5.2 in Griffiths before Monday. I'll also explain how the op-amps we used work during one of the lab sessions.

Monday's lab & lecture

Monday, we'll start with basic dc circuit analysis. The lecture will mainly cover current, voltage, and resistance, but we will discuss quite a few general rules for circuit analysis.

After the lecture portion of the class, we'll finally get to that lab I wanted to do Wednesday, constructing an opto-isolator. Here's the circuit diagram you'll need (click for a larger version).
Monday's lecture will be mostly practical knowledge, though we will cover some general things like Kirchhoff's rules and Thevenin equivalents briefly.

Wednesday, we'll discuss more general aspects of electrical conduction, dissipation, and circuit networks. We'll also attempt to build an amplifier. As mentioned in the previous post, the reading for this week is from my ph102 notes, or any decent book on dc circuits you have handy.

HW 4 is out

Here you go. More than you ever wanted to know about circuits.

The topics for Wednesday's problems will all be covered in tomorrow's lecture. For this week, we are more or less abandoning Griffiths, since he doesn't cover circuits very much.

You might find my ph102 notes useful in the mean time. Chapter 3, section 3.6 covers capacitors, chapter 4 covers current & resistance, and chapter 5 covers basic dc circuits.

Reading for next week

Next week, we'll start to discuss circuits, having learned enough about electrostatics to do something practical. The Griffiths book has next to nothing on circuits, so I'm supplementing this material with my own notes, which you can find here. [23Mb PDF]

For Monday (21 Sept), please read sections 3.6 & 3.7 along with the whole of Ch. 4, covering capacitors and electric current. It should be light reading - almost no math.

For Wednesday (23 Sept), please read Ch. 5, covering basic dc circuits.

(Chapters 2 and 3 might be worth skimming to make sure you've got the qualitative aspects of electrostatics down, if you have time. It is all stuff we covered already, but sometimes the math hides the qualitative understanding ...)

Reading this week

Wednesday, we'll mostly be talking about sections 2.5.1-2.5.3 in Griffiths (conductors), which is really just applying what we have learned already to a specific situation involving mobile charges. Hopefully this will not take a huge amount of time, and we can spend some time setting up the homework problems for this week.

Friday, we'll begin with capacitance and discuss the method of images briefly. Before then, have a look through sections 2.5.4 and 3.2.1-3.2.4.

Next week, it is on to chapter 4 for the most part - except for a bit on image charges (Friday) and dipole moments (this week's homework), we will skip the bulk of chapter 3. If you want to get a head-start, for Monday it would be good to read sections 4.1.1-4.1.4. These will make more sense after you finish the last of this week's homework problems on dipoles ...

Reading for Wednesday

For Wednesday, make sure you have read Griffiths Chapter 2 through the end of section 2.4.

Today, we'll cover 2.1 and 2.2.

Additional reading that might help

You might also find Chapter 2 in my PH102 notes useful, for a more qualitative introduction to electric forces and fields.

Homework 1 problem 9

Reminder: you do not have to do problem #9 on HW1. Full solutions to HW1 will be out tomorrow.

Homework 2 will come out tonight or tomorrow, I'll post it here. It will be less tedious, and at least raise the possibility of cleverness saving you some work.

For Monday, please read sections 2.1-2.2 in Griffiths. Study the problems in those sections carefully (this should be easier now that you have your little present from this morning). Warning, the solutions guide can be quite terse.

Looking at my old PH106 content might also be clever. For now, you might want to look at the first HW set, it is very much like what we started on today. (My solutions are sometimes much more lengthy than they need to be, I was trying to be as explicit as possible.)

Reading for the next days

By Friday, it would be good if you had read the first chapter of Griffiths. We have basically covered sections 1.1, 1.2, 1.4, and 1.5 at some level, so you should be able to skim those. Friday we'll worry about section 1.3, which is the last thing we need to get started with proper E&M ... so read section 1.3 with a little more care. We will not cover section 1.5 just yet, but will introduce the Delta function once we need it ... but please at least skim that section in the mean time.

For Monday, we'll start on Chapter 2 of Griffiths. Please have a look through sections 2.1 and 2.2, we should get through that much on Monday.

We will also start doing labs on Monday, details to follow soon.