Unit 4

Unit 4

Unit 1 • Unit 2 • Unit 3 • Unit 4 • Unit 5 • Unit 6 • Unit 7 • Unit 8

Electromagnetic Energy and Momentum

October 15 to 23

You should review the notes and videos below by October 23.
Your response to Discussion Question 4.1 is due Tuesday, October 20, at 5pm
Your solutions to Problem Set 7 are due Thursay, October 22, at 5pm

In this unit we extend the ideas of energy and momentum to electromagnetic fields, defining the energy and momentum densities, and the energy and momentum currents. We show how these enter conservation laws for the total energy and momentum of a system of interacting charges. We also discuss the capacitance of a system of conducting bodies, and the inductance of a system of current carrying loops. We discuss the electromagnetic and magnetostatic energies stored in these configurations. We review the properties of electromagnetic waves in a vacuum, and discuss the energy and momentum carried by such waves. In supplemental notes, we discuss the force, torque, and interaction energy of electric and magnetic dipoles.

Below is a list of links to the course notes for each topic in this unit, followed by links to recorded video lectures. Following these topic-links are links to the unit Discussion Boards and the unit Problem Set.

Notes and Video Lectures

Notes 4-1 - Electromagnetic energy density and the Poynting vector
Notes 4-2 - Electromagnetic momentum density, the Maxwell stress tensor, and the force on a conductor's surface
Notes 4-3 - Capacitance and Inductance
- Video 4-3.1 - Capacitance matrix between conducting bodies [33 min]
- Video 4-3.2 - Mutual inductance matrix between current carrying loops [13 min]
Notes 4-3-supp - Supplemental: Forces, Torques, and Interaction Energy of Electric and Magnetic Dipoles
Notes 4-4 - Energy and momentum of an electromagnetic wave in a vacuum
- Video 4-4.1 - Harmonic plane electromagnetic waves in a vacuum [40 min]
- Video 4-4.2 - Energy and momentum in harmonic plane waves [16 min]

Discussion Board for Unit 4
Use this link to post questions regarding the material in Unit 4. Questions and replies will be viewable by the entire class. To post a question, click on the Create Thread link on the top of the Discusson Board page. To get an email message whenever someone makes a post, click on the Subscribe link on the top of the Discussion Board page.

Discussion Question 4.1 - Due Tuesday, October 20, at 5pm
In the Notes 4-1 you will find Discussion Question 4.1. Use this link to post your brief response to this question. You may view responses only after you have posted your own response. To post your response, click on the Create Thread link on the top of the Discusson Board page.

Problem Set 7 - Due Thursday, October 22, at 5pm
You must scan or take a photo of your solutions, collate them into a single multi-page pdf file, and upload it to Blackboad using this link.