## Welcome to PHY 482 ### Electrodynamics Prof. Danny Caballero

### Contacting Danny Office: 1310-A BPS Email: <caballero@pa.msu.edu> Cell phone: 517-420-5330 (texting is fine)

### Important Sites * Course Webpage: [dannycab.github.io/phy482msu_s2019/](http://dannycab.github.io/phy482msu_s2019/) * Discord Group: [discord.gg/FcktcXz](https://discord.gg/FcktcXz)

### Course Activities * Projects: * 2 of them; Mar 1 & Apr 29 - 20% each * In-Class Quizzes: * 7 of them; Every other Friday; 1 dropped - 20% * Homework: * 14 of them; Due on Fridays by 5pm; 1 dropped - 40% * Clickers: * Pure Extra Credit - up to 2% bonus [Much more detail on website](http://dannycab.github.io/phy482msu_s2019/)

Learning is a social and collaborative act! ### Homework Help Session **Evening session once per week (Location TBD)** Question to you: When should we do this? Reminder: Homework is due on Fridays (expect this first one).

## This Week!!! * Homework 1 is already up (Due Fri. Jan. 11 at 5pm) * Read (seriously do this!) * Griffiths Ch 7.1.1-7.1.2 (Review? Chs 1-6) * [Download Anaconda distribution of Python](https://www.continuum.io/downloads) **Stay up-to-date by checking website, calendar, and discussion forum regularly.**

### Computational Homework problems * We will be using Python on homework problems this semester. * Installation instructions appear on the piazza site. * Homework solutions should take the form of a Jupyter notebook, which you can print to PDF and turn in. * If you get stuck somewhere, post on Discord, so your classmates benefit from your question.

### Projects #### Individual Project (Mar. 1) * Literature review of some interesting topic in E&M (4-5 pages) * Homework questions will support you on this * See syllabus for sample questions * Paper should be typed, inline references, bibliography, etc. * Evaluation rubric is online

### Projects #### Pair Project (Apr 29) * Poster presentation of an original contribution (theory and computation) * Homework questions will support you on this * See syllabus for sample questions * Can be something that has been done before that you just extend * Evaluation rubric is online * There will be a significant self-evaluation component to this also

# Questions?

## What do you think PHY 482 is about?

### Electromagnetism is the foundational field theory of physics Think about everything you already know about electromagnetism (it's a lot already!). Work with a partner to map out the electromagnetism concepts that you know and how they are related to each other.

5 charges, q, are arranged in a regular pentagon, as shown. What is the E field at the center? <img src ="./images/5charges.png" align="center" style="width: 250px";/> 1. Zero 2. Non-zero 3. Really need trig and a calculator to decide Note: CORRECT ANSWER: A

<img src ="./images/zappa.jpeg" align="right" style="width: 100px";/> 1 of the 5 charges has been removed, as shown. What’s the E field at the center? <img src ="./images/4charges.png" align="center" style="width: 400px";/> 1. $+(kq/a^2)\hat{y}$ 2. $-(kq/a^2)\hat{y}$ 3. 0 4. Something entirely different! 5. This is a nasty problem which I need more time to solve Note: CORRECT ANSWER: B Superposition!

To find the E-field at P from a thin line (uniform charge density $\lambda$): <img src ="./images/linecharge.png" align="right" style="width: 400px";/> $$ \mathbf{E}(\mathbf{r}) = \dfrac{1}{4\pi\varepsilon_0}\int \dfrac{\lambda dl'}{\mathfrak{R}^2}\hat{\mathfrak{R}}$$ What is $\mathfrak{R}$? 1. $x$ 2. $y'$ 3. $\sqrt{dl'^2 + x^2}$ 4. $\sqrt{x^2+y'^2}$ 5. Something else Note: CORRECT ANSWER: D

What do you expect to happen to the field as you get really far from the rod? $$E_x = \dfrac{\lambda}{4\pi\varepsilon_0\}\dfrac{L}{x\sqrt{x^2+L^2}}$$ 1. $E_x$ goes to 0. 2. $E_x$ begins to look like a point charge. 3. $E_x$ goes to $\infty$. 4. More than one of these is true. 5. I can't tell what should happen to $E_x$. Note: CORRECT ANSWER: D (A and B)

Given the location of the little bit of charge ($dq$), what is $|\vec{\mathfrak{R}}|$? <img src ="./images/sphereintegrate.png" align="left" style="width: 300px";/> 1. $\sqrt{z^2+r'^2}$ 2. $\sqrt{z^2+r'^2-2zr'\cos\theta}$ 3. $\sqrt{z^2+r'^2+2zr'\cos\theta}$ 4. Something else Note: CORRECT ANSWER: B

Which of the following are vectors? (I) Electric field, (II) Electric flux, and/or (III) Electric charge 1. I only 2. I and II only 3. I and III only 4. II and III only 5. I, II, and II Note: * CORRECT ANSWER: A

A positive point charge $+q$ is placed outside a closed cylindrical surface as shown. The closed surface consists of the flat end caps (labeled A and B) and the curved side surface (C). What is the sign of the electric flux through surface C? <img src="./images/ABC_cylinder.png" align="center" style="width: 600px";/> 1. positive 2. negative 3. zero 4. not enough information given to decide Note: * CORRECT ANSWER: B * This is meant to be hard to visualize, next slide illustrates it better.

Let's get a better look at the side view. <img src="./images/ABC_cylinder_side.png" align="center" style="width: 350px";/>

Which of the following two fields has zero divergence? | I | II | |:-:|:-:| | <img src ="./images/cq_left_field.png" align="center" style="width: 400px";/> | <img src ="./images/cq_right_field.png" align="center" style="width: 400px";/> | 1. Both do. 2. Only I is zero 3. Only II is zero 4. Neither is zero 5. ??? Note: * CORRECT ANSWER: B * Think about dE/dx and dE/dy * Fall 2016: 7 [34] 13 43 3; (Asked them to consider dvx/dx and dvy/dy) 3 [90] 3 4 0