- #1
Silviu
- 624
- 11
Hello! I am confused about the first EM problem on http://web.mit.edu/physics/current/graduate/exams/gen2_F00.pdf (page 4, with the cylinder in a magnetic field). The solution can be found http://web.mit.edu/physics/current/graduate/exams/gen2sol_F00.pdf. In part a the solution is straightforward. However I am a bit confused about part b. They divide the cylinder in solenoids and calculate the field a a given point produced by these solenoids. This makes sense. However, when they plug in the value of ##j(t)## they use the value from part a, and I am not sure why we can do this. In a simple RL circuit you have an ODE that you solve to find the current as a function of time. Here if I understand well, they calculate the induced magnetic field created be ##j## from part a, and use that to calculate the new ##j##, but once you take self inductance into account, ##j## from part a is not there anymore. Don't you need to calculate the magnetic field induced by this new ##j## to find ##j## at a later time, and this way you need an ODE? What am I missing here?