Electric field lines

We have made a small demo that will allow you to play around with electric field lines in your web browser. You can place and move around charged particles to see how the field changes as you make your own charge configuration.

An electric field line simulator straight in your browser!

Try the simulator here

Note that there are some limitations to this simulation, leaving it a bit unphysical when it comes to lines that might end up in open space, wrong field line density and other quirks. All in all it should be correct to a decent approximation, though.

For the programming enthusiasts out there, the simulation is created using Javascript and HTML5. You can check out the source code here.


Note on the magnetic vector potential

Magnetic dipole (Source: Wikipedia*)

In electrostatics we found it very convenient to introduce the concept of the electric potential. It gave us a straight forward way of calculating electric fields without doing any vector calculations or using any symmetry arguments. Can we introduce something similar for magnetic fields?  It turns out that because magnetic fields are divergence less we can find a vector potential who’s curl gives us the magnetic field! Even though this magnetic vector potential is not as useful as the electrostatic potential in elementary applications, it turns out to be of major importance in electrodynamics as well as classical mechanics and quantum mechanics. It might therefore be a good idea to get familiar with the concept and some of it’s properties already, especially if you are taking a degree in physics. In this note I explain how to find the vector potential, the concept of a gauge transformation and it’s fundamental equations relating it to currents in both electrostatics and electrodynamics. Read more here:

* Image found at http://en.wikipedia.org/wiki/File:VFPt_dipole_magnetic3.svg / CC BY-SA 3.0

Midterm exam

There came in some questions regarding the relevance of the weekly exercises considering the upcoming midterm exam. The answer is that the weekly exercises of course are relevant and therefore valuable practice. The questions for the exam might include everything that has been lectured up to and including the lecture 04.10 where the main subjects will be electrostatics, currents and magnetostatics. The lecture plan for the semester is found here:


Remember that you can bring an A4-paper with your own notes and allowed mathematical and physics tables (Rottman, Angell/Øgrim og Lian) as well as an approved calculator.

Update: There will be group lessons on Tuesday, 11 October, but no group lessons on Friday, 14 October.

Electromagnetic java simulations

The java simulations that Andreas Görgen showed in the lectures can be found here:

The two first ones allows you to set up charge distributions and visualize fields, field lines and equipotentials. The third one comes with some preconfigured and interesting charge distributions where you can do things such as taking the flux integral of the field. As a recommendation for link 3 try out; setup: charged plate dipole, mouse: surface integral and see how you change the field by varying the the size of the plates. In one limit you get the familiar dipole field, while in the other you get the field from a parallel plate capacitor.