Tomorrow Lab #2 Begins

The second of five labs for the course begins tomorrow. You can find the lab document by clicking on the lab #2 menu tab at the top of this web page.

We won't cover magnetostatics for a little bit yet, but the lab is straightforward so I am willing to bet you will handle it well.

PA Questions

If anyone has any particular questions, or just suggestions for what area of the course to focus on, please add your comments to this posting. We will try our best to cover those areas in the next PA.

Electrostatic Energy

Today's lecture started out with Green's Theorem. Combining the point form of Gauss's Law with the integral form of Gauss's Law, one can show that the flux of the electric field is related to the divergence of the electric field by the Divergence Theorem, which is a specific example of the more general Green's Theorem.

Next, we derived the expressions for the amount of electrostatic potential energy stored in a collection of charges. We looked at both discrete charge assemblies, and also continuous distributions of charge.

We covered one example problem (find the amount of work required to assemble a ball of charge of radius "b" and charge density "rho").

Lastly, we looked at the electrical flux density, about which we will have more to talk about next week. So please read up on flux density. You should also read about boundary conditions.

New Poll Up

Another week, another poll. Please answer truthfully. And one time only!

Failures

Ok, so the poll from last week is closed. Could those of you who wish to fail please send me an email so I can enter in your marks from now? No need to write the exam. Hopefully I will see you again next year.

PS: My goal is to have no failures this year. Please help me make my dream come true!

Yesterday's Lecture

Ah yes, the lecture of yesterday. Who remembers it?

We covered divergence, which involved a derivation for the divergence expressed in Cartesian co-ordinates. Then we combined the divergence concept with the integral form of Gauss's Law, and arrived at the differential form of Gauss's Law (also known as the point form). After that, we used the fact that the electric field vector is given by the negative gradient of the voltage potential, substituted that into the point form of Gauss's Law, and presto mundo we had Poisson's equation. Setting the volume charge density to zero then led to Laplace's equation.

We tried one practice problem, which was to use Laplace's equation to find an equation for the voltage in the region between two parallel plate conductors of known potential and known separation distance. From the voltage equation we found the electric field between the plates.

I pointed out that the electrical field is constant, and increases with increasing plate voltage difference and decreasing plate separation. This has important ramifications for capacitor design (e.g. allowable dielectric, voltage rating).

PA #1 Solutions Update

Ali slightly adjusted his solutions for PA #1. I updated the downloadable copy.

Failure Rate in ELEC 3105

As I write this, 55 people have voted in the poll about mark expectations, with 26 votes cast for an "F" mark in the course. Since there are only 34 students currently registered in the course, I can only assume that some students plan on failing multiple times?

PA #1 Solutions

Ali sent me the solutions to the first PA session questions.

Upcoming PA Questions

I asked Hassna to go over the solutions to the following questions from the THIRD edition of Sadiku: 4.32, 4.33, 4.34, 4.35, 4.39, and 4.41. She will cover them plus a few from the FIFTH edition. I am waiting for her to confirm which ones --- when confirmed, I will edit this post and add them here.

PASS Calendar

Rachel sent the PASS calendar to me, which you can download and view.

Conductors in Electrical Fields and Equipotential Surfaces

Today we mostly covered conductors in electrical fields and equipotential surfaces. We also started divergence of the electric field, which will lead us next week directly to Poisson's equation. Please read up on divergence and Poisson's equation.

Voltage Stuff

Today I finished off voltage potential. We looked at voltage potential arising from various charge distributions. I gave some clarification concerning the sign on the "work equation". We looked at how to get the electric field from the voltage function. We solved an example problem for a ring of charge and the associated voltage potential along its axis.

You should try to take the voltage we derived for the ring, find its gradient, and see if that answer is the same as the one you found during your PA session.

I was happy to see a few more people volunteering answers in class. Interactivity is welcome in my lectures, and no one should feel shy to speak out!

PS: Here is the solution to the little problem I gave last Friday, courtesy of your classmate Kenneth. The objective was to look at each motion path around a charge, and decide if moving a test charge along that segment would require you to input energy, have the field release energy, or result in no change of potential energy.

Yannick Wins!

Yannick noticed an error in the first lab, and for that he automatically earns an A+ in the course*. The error was following equation (5), and the statement was that cos(90)=1, which is clearly not true.

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* A+ dependant on total marks earned in the course, of course.

Rico Wins!

Well there you go, Rico is the best penguin. But we already knew that!

Tomorrow's Lab

Tomorrow I have a MASc defence starting at 2pm, so I will not be coming to the start of the lab.

If there are any problems that the TAs cannot resolve, please send me an email --- I will keep an eye on my email during the defence.

I will drop by as soon as the defence concludes, probably between 4pm and 4:30pm.

Good luck.

Saturday Break

You can't work all the time. You might like my cousin appearing at the NAC tonight. You can find her band on YouTube.

Enjoy your Saturday!

Thank You

Thank you for showing up for a late Friday lecture despite the miserable weather.

Today we finished off some examples of electric fields due to charge distributions. We used Gauss's Law to find the field for an infinite charged line and an infinite charged plane. We discussed the physical meaning of these problems. Then we moved on to voltage potential, and discussed the meaning of voltage potential in terms of the amount of work required to place charges in certain configurations.

Gaussian Surfaces and Electric Flux

Yeah, it can be confusing. However, learn the concepts and then do practice problems until it makes sense.

Here are the slides I used today. Please review the two examples I did not cover today, and we will look at them Friday.

Important Matters

Item #1: New poll on the right side of the page.

Item #2: Lab #1 will be posted shortly. Check the tabs at the top of the page.

PA Locations and Times

For the rest of the term, the PA sessions will be held as follows:

Mondays, 2:35-5:25pm, 411SA

Tuesdays and Thursdays, 2:35pm-5:25pm, 4124ME

I am updating the calendar page on this blog later today.

PA Session Info

The email I just sent to your TA:


Ali,

This is a large email, so please confirm that you received it ok.

Can you please cover the following topics during the upcoming PA sessions? If the students say they already know something, then spend minimal time on it. No sense in boring them to tears.

Review Material

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1. Coordinate systems (cartesian, cylindrical, and spherical). The students should know how to specify a point, a differential surface element, and a differential volume in each coordinate system. The review questions 3.1, 3.2, and 3.3 are quite helpful in the attached PDF, taken from Sadiku, 3rd edition. The students also need to know how to find a unit vector in each coordinate system, given two points.

2. Divergence. Focus on Cartesian coordinates. Source material is in the attached PDF.

3. Laplacian. Focus on Cartesian coordinates. Source material is in the attached PDF.

Practise Problems

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So far we've covered Coulomb's Law, the electric field, sketching field lines, and electric fields for continuous charge distributions. Covering a few problems about continuous charge distributions would be helpful.

I asked the students to calculate the electric field from an infinitely long line of charge at a distance R from the line, where the linear charge density is rho_s. Can you go over the solution to this problem with them, and ask them to aid in the solution --- in other words don't just feed them the solution. There are a number of ways to solve this, including using Gauss's Law (we did not cover Gauss's Law yet). A good solution to the problem is attached as a PDF.

Can you also cover:

-- the electric field on the axis of a disk of charge. See attached PDF.

-- use the previous problem solution to solve for the electric field above an infinite sheet of charge. See attached PDF.

-- the electric field on the axis of a ring of charge. There is a solution to this one here: http://youtu.be/80mM3kSTZcE

I don't know how long this will take. Don't freak out if you can't cover it all!

Electric Fields Lecture

Today we looked at electric fields from point charges, line charges, surface charges, and volume charges. We tried one problem involving a line charge, but many students saw it before in a physics lecture. I suppose that is ok, since this is only the second lecture. Let me know though if there is too much repeated material.

So far I am leaning toward a class intelligence that is not near a sack of potatoes.

The question to ask yourselves: is it better to remain silent and be thought a fool, or speak out and remove all doubt? (Little Friday night joke there for all of you studying ELEC 3105, as I know you all are, right?!)

PA Sessions Next Week

Ali will lead the PA sessions next week. The sessions will be held as follows:

Monday, 2:35-5:25pm, 411SA
Tuesday, 2:35pm-5:25pm, 4124ME

Thursday, 2:35pm-5:25pm, 4124ME

PASS Sessions

I received the following message this morning:

PASS (Peer Assisted Study Session)
Facil: Rachel Katumba
Email: pass@carleton.ca

PASS is:
 A pre-made study group.
 A chance to meet new people.
 An opportunity to get a kick-start on studying.
 A fun and friendly place to go over course material.
 A ready-made review session.
 A license to avoid cramming.

PASS is NOT:
 Not a tutorial.
 Not another lecture.
 Not mandatory.
 Not evaluative.

PASS supports this class because it is a traditionally difficult course.
PASS Workshops will be held twice a week for 1.5 hours. Both workshops cover the same material.

Below are three time slots, we will decide on the best two out of three time slots on Wed Jan 11.
 Wed 6 – 7.30 pm
 Fri 1 – 2.30 pm
 Fri 2.30 – 4 pm

Note: Workshops begin in the week of Jan 16.

Introductory Lecture

Today I introduced myself to the class and showed a few projects from my research team that involved material from ELEC 3105.

We then started on basic electrostatic theory, specifically Coulomb's Law.

For next lecture, if you could please review some vector material from a previous math course that would be helpful.

Also, you might find some videos on YouTube helpful. I like the ones by a user named "derekowens". Just go to YouTube and check out his channel, especially the videos concerning Coulomb's Law.

Please post links to any excellent course-related videos in the comment section below.

Or, any funny videos at all.

Well Hello There.