TPR #5, question 28 (Magnetism and Torques on a Coil)

[bluebillion]

---

Members do not see this ad.

There is a magnetic field pointing to the right and a coil in the middle with a counterclockwise current. Why does the coil rotate clockwise? From what I understood, there are opposing magnetic forces going into and out of the page. Shouldn't they cancel each other out?

I feel like I am not understanding something basic. I have attached the file with the answer.

 

[Oso]

You're thinking of translational equilibrium, in which equal forces in opposite directions cancel out.

This problem is about rotational motion (torques), in which opposite forces about a pivot point cause the object to rotate.

Note that this problem has a magnetic FIELD everywhere, but the magnetic FORCE is only applying at the points where there's current that's not parallel/anti-parallel to the magnetic field (the 2cm sides).

Take a book. If you apply a downwards force on one long edge and an upwards force on the opposite edge, the book will begin to rotate.

 

[bluebillion]

thanks for the explanation 🙂

 

[Oso]

No problem! Good luck!