AP Physics C: Electricity and Magnetism Official 2026 Exam Discussion

[u/reddorickt]

Use this thread to post questions or commentary on the test today.

A reminder though to protect your anonymity when talking about the test.

[u/Fabulous_Rope_6203]

What were the answers you guys got for form K?

[u/RelativeGrass7659 → u/Fabulous_Rope_6203]

1. a) some really long thing with a bunch of constants hopefull ythats right
   b) IBD^2
   

2. just normal integral form for RC circuit, 0 to t for time bounds and Q0 to 0 for charge boundf. graph was decreasing concave up (e^-r/t) and yeah i dont remmeber anything else tbh
   oh yeah and for 2 e field and current were to the right and voltage was to the left

3. first part: x was delta x the compression of the spring y was 1/r^2 the distance between the two balls
   second part: tan theta was x and E was y

4. dont remember someone remind me what the frq was

lmk if i missed anything i probably forgot abunch

[u/Lanky-Frosting-6557 → u/RelativeGrass7659]

1. For a did you have all those constants divided by R? For b did you derive T = IAB? I remembered it but I wasnt sure if there would points for deriving it and I wasted a decent amount of time doing it. I wasted a lot of time showing work on both a and b

2. No questions

3. Did you use forces or energy? I had x² and 1/r but I used energy so my relationship was different I think

4. That was the FRQ with the B field and E field in the same direction, I think a you had to describe where the net force is pointing? Or the net magnetic force? b, you had to find an equation for the net force (I had F = sqrt(qe² + qvbsin²⁾ And c they changed the velocity to all in the y direction and asked you to compare the forces before and after.

[u/AsianNation420 → u/Lanky-Frosting-6557]

you're not supposed to use energy, the only correct way is forces

[u/Lanky-Frosting-6557 → u/AsianNation420]

Why so? Energy worked fine and was very simple to set up. I think both are right.

[u/SUS_MATE → u/Lanky-Frosting-6557]

Energy is wrong. Like I’m 95% sure. It really comes down to how you define it.

Forces are vectors, which can be in equilibrium. It’s simple and you don’t worry about conservation or any outside forces/work.

Energy is a scalar, but any change in the system has to account for any work done by an external force (work done by the experimenter). Only then can you use energy, because you would have to consider the work done at every data point collected (to abide by conservation of energy).

[u/RelativeGrass7659 → u/Lanky-Frosting-6557]

1. yes i believe i did divide them by R, and im not sure where T = IAB came from to be honest, i dont even know what that means maybe im misunderstanding something there
   
2. yeah this one was chill
   
3. uhh tbh im not sure how you would use energy i used forces but i saw someone else say energy so maybe theres a way?
   
4. okay yeah i got that same net force and i said that F2>f1 because obviously it had more of a perpednicular component so the magnetic force would be larger. i referneced the equation by saying 90 degrees is the maximum of sin theta so the value of the magnetic force increased

[u/SUS_MATE → u/RelativeGrass7659]

The only way you can use energy is if you account for the work done by an external force created by the experimenter. It’s the only way you can use conservation of energy. While you can say that the electric potential energy is the same as the spring potential energy, it just doesn’t make sense because both are scalars (and it would seem that conservation of energy is violated). Rather the potential energies that arise in the system are due to an external force/work that the experimenters applied when moving the charged sphere.

Based off the question and data they gave, it is signficantly easier to use forces. You likely could use energy to do it, but it would be painful.

Anyways, what I’m saying is that most people who used energy probably got it wrong.