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.]
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