PHYS 212, Honors Section – Review Material


Chapter 29: Magnetic Fields

  • Basic facts: Attraction and repulsion; N and S magnetic poles; Magnetic vs non-magnetic materials.
     
  • Field lines: Direction in which they point; Do they start and/or end anywhere?
     
  • Earth's magnetic field: Qualitatively; The average value is about 0.5 G = 5.0 × 10–5 T.
  • Magnetic force on a moving charge or current: Given by, respectively,

F = q v × B,  or  F = |q|vB sinθ ,   and   F = I L × B,  or  F = ILB sinθ .

You can find the direction from the right-hand rule. The units of B are tesla, 1 T = 1 N·s/C·m.

  • Hall effect: Be able to describe qualitatively what happens and the origin of the Hall voltage.
     
  • Path of a particle: In a constant magnetic field, a particle with velocity perpendicular to B moves on a circle with

r = mv/|q|B.

What happens qualitatively to a particle whose velocity is not perpendicular to B, or one moving in a non-constant magnetic field, such as the Earth's.

  • Torque on a current loop: Qualitatively, what happens to a loop of current when placed in a magnetic field, and along what direction the loops tends to align itself; The magnetic dipole moment of the loop and the torque on it are given by

τ = μ × B ,  with   μ = NIA .

  • [Potential energy of a magnetic dipole: Given by U = –μ·B.]

Note: You are not required to know the topics and equations inside square brackets.

Website by Luca Bombelli <bombelli"at"olemiss.edu>; Content of this page last modified on 8 may 2011