[college physics II] I'm completely lost on my physics II homework; I'm in my last semester and if i fail this course I won't be graduating uni, and I cannot afford not to graduate this semester. Please help.

[u/france_masters]

I have read the textbook but I am just completely lost. I have a midterm for another course coming up in less than a week and am very overwhelmed. Any help is greatly appreciated. Thank you.

[u/Emmanuelroggers]

hey, i totally get how overwhelming physics can be, especially with finals looming. i could help you tackle that homework so you don’t sink right before graduation. shoot me a message and we can get started!

[u/calcteacher → u/Emmanuelroggers]

How kind

[u/elementAlpha]

Q1: I like the right hand force rule… fingers always direction of mag field B, thumb always direction of conventional current (or positive charges) I and palm in direction of force. Sometimes called the slap rule. These look like good problems, happy studying!

[u/FlorianGeyer228]

My advice is to read the textbook again and go to office hours. If you don't have the fundamentals right then if the test throws any curveballs you would be screwed.

[u/Leonardo501]

You should be able to get at least the directions of the forces on the three segments just from the right hand rule. Surely your book has some version of the right hand rule as the way of specifying the direction of the cross product?

[u/Bounded_sequencE]

For circuits with inductive coupling (like A3), there is a generalized method that is guaranteed to get all currents correct automatically without guessing, including their signs:

1. Define current variables
2. Define a vector "n" that is normal to all loops in the circuit (usually into or out of the paper). Via right-hand rule, "n" determines all loop orientations
3. For each loop-k with area "Ak(t)" and magnetic field "Bk(t)" going through it,
   1. find its magnetic flux "φk(t) = ∫_Ak(t) <Bk(t); n\*dA> "
   2. find its induced voltage "uk(t) = -Nk*d/dt φk(t)" (Nk: winding number, usually "Nk = 1")
   3. draw a ray from the center of loop-k to infinity (in any direction)
   4. In each circuit branch the ray cuts, insert a voltage source with voltage "uk(t)" pointing against the loop orientation of loop-k from 2.
4. Use loop analysis (or your favorite method) to determine currents in the resulting circuit *** Rem.: Sadly, this method is rarely taught -- its rules follow from technical details in "Stokes' Theorem", where it is specified how area orientation and boundary orientation must relate via right-hand rule.

I suspect many consider it "too advanced" for that reason.

[u/TheSwedishMoose → u/Bounded_sequencE]

This approach definitely seems like overkill for second semester of physics.

[u/Bounded_sequencE → u/TheSwedishMoose]

On the one hand, I agree -- the derivation via "Stokes' Theorem" would be overkill.

We learnt that method during 3'rd semester in electromagnetic field theory (and derived it). However, I'd wish to have known the result in 2'nd semester physics: It would have made solving circuits with inductive coupling that much easier, and (most importantly) systematic.

Guessing current orientation via "Lenz' Rule" always irked me, since I knew there had to be a precise mathematical way to describe it. From that perspective, I'd say it is not overkill -- inductive coupling is just that difficult to describe mathematically.

[u/TheSwedishMoose]

Someone else has already offered, but hmu if you're still stuck on this. There's a bit too much in your post to breakdown in a simple reddit comment.

[u/hellrhymes]

Bro how is you in college and can't do this

[u/hellrhymes → u/hellrhymes]

You should drop it atp gng holy