Uncategorized – Elektromagnetisme http://elektromagnetisme.no The home of FYS1120 Mon, 20 Oct 2014 11:23:54 +0000 en-US hourly 1 https://wordpress.org/?v=4.9.3 28429679 Old exam problems http://elektromagnetisme.no/2013/11/21/old-exam-problems/ http://elektromagnetisme.no/2013/11/21/old-exam-problems/#comments Thu, 21 Nov 2013 13:45:01 +0000 http://elektromagnetisme.no/?p=2415 We have compiled a zip-file with a bunch of old exams, as well as their solutions. The newer ones, 2011 and 2012, are most relevant.

Good luck!

]]> http://elektromagnetisme.no/2013/11/21/old-exam-problems/feed/ 6 2415 Electric field lines http://elektromagnetisme.no/2012/09/05/electric-field-lines/ http://elektromagnetisme.no/2012/09/05/electric-field-lines/#respond Wed, 05 Sep 2012 19:31:12 +0000 http://elektromagnetisme.no/?p=1423 Continue reading →]]> 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.

Enjoy!

]]> http://elektromagnetisme.no/2012/09/05/electric-field-lines/feed/ 0 1423 Note on the magnetic vector potential http://elektromagnetisme.no/2011/10/27/note-on-the-magnetic-vector-potential/ http://elektromagnetisme.no/2011/10/27/note-on-the-magnetic-vector-potential/#respond Wed, 26 Oct 2011 22:29:56 +0000 http://mindseye.no/?p=992 Continue reading →]]>

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

]]> http://elektromagnetisme.no/2011/10/27/note-on-the-magnetic-vector-potential/feed/ 0 992 Midterm exam http://elektromagnetisme.no/2011/10/05/midterm-exam/ http://elektromagnetisme.no/2011/10/05/midterm-exam/#comments Wed, 05 Oct 2011 17:46:52 +0000 http://mindseye.no/?p=924 Continue reading →]]> 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:

http://www.uio.no/studier/emner/matnat/fys/FYS1120/h11/undervisningsplan.xml

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.

]]> http://elektromagnetisme.no/2011/10/05/midterm-exam/feed/ 4 924 Electromagnetic java simulations http://elektromagnetisme.no/2011/09/13/electromagnetic-java-simulations/ http://elektromagnetisme.no/2011/09/13/electromagnetic-java-simulations/#respond Tue, 13 Sep 2011 18:56:06 +0000 http://mindseye.no/?p=848 Continue reading →]]> 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.

]]> http://elektromagnetisme.no/2011/09/13/electromagnetic-java-simulations/feed/ 0 848 The FYS1120 Weekly Assignment Post #2 http://elektromagnetisme.no/2010/09/28/the-fys1120-weekly-assignment-post-2/ http://elektromagnetisme.no/2010/09/28/the-fys1120-weekly-assignment-post-2/#comments Tue, 28 Sep 2010 21:33:43 +0000 http://mindseye.no/?p=238 Continue reading →]]> Allright! Here are my solutions to this weeks assignment. If you have any questions just post them here and someone might just help you out. The same goes if the solutions are not in agreement with your own.

Assignment #6

1)

a) E =\frac{E_0}{\kappa_1} \ \ 0 < y < d/2 \ \ \, E = \frac{E_0}{\kappa_2} \ \ \ d/2 < y < d

\Delta V = \int_0^d \vec{E} \cdot \vec{dy} = \frac{E_0 d}{2 \kappa_1} + \frac{E_0 d}{2 \kappa_2} = \frac{E_0 d}{2} \left( \frac{ \kappa_1 + \kappa_2}{\kappa_1 \kappa_2}\right) = \frac{Qd}{A\epsilon_0 2} \left( \frac{ \kappa_1 + \kappa_2}{\kappa_1 \kappa_2}\right)

b) C = \frac{Q}{\Delta V} =\frac{2Q}{E_0 d}\left(\frac{\kappa_1 \kappa_2}{\kappa_1 + \kappa_2}\right) = \frac{2A\epsilon_0}{d}\left(\frac{\kappa_1 \kappa_2}{\kappa_1 + \kappa_2}\right)

c) C = \frac{A \epsilon_0}{2d} (\kappa_1 +\kappa_2)

2)

a) R = \frac{\rho}{A_0 \alpha} \ln(1+L\alpha)

b) L’Hopital

c) Hmm.. not yet sure.

3)

a) E = \frac{D}{\epsilon_0 \kappa} = \frac{Q}{4\pi \epsilon_0 \kappa} \frac{1}{r^2}

b) C = \frac{Q}{4 \pi \epsilon_0 \kappa} \left(\frac{b-a}{ab}\right)

c) Q_a = Q_b \Rightarrow \sigma_b = (\frac{a}{b})^2 \sigma_a

d)\sigma_a = \hat{n}\cdot \vec{P} = \sigma \frac{\kappa -1}{\kappa} \ \ \ r=a

\sigma_b = \sigma \frac{a^2}{b^2} \frac{\kappa - 1}{\kappa} \ \ \ r=b

4)

a) I_1 = \frac{12}{11}A, I_2 = \frac{8}{11} A , I_3 = \frac{4}{11} A

b) P = I\epsilon = 8.72 W

c) P = P_1 + P_2 + P_3

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