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Magnetism Rapid Review for AP Physics B & C

By — McGraw-Hill Professional
Updated on Feb 12, 2011

For a more thorough review, refer to these concepts:

Rapid Review

  • Magnetic fields can be drawn as loops going from the north pole of a magnet to the south pole.
  • A long, straight, current-carrying wire creates a magnetic field that wraps around the wire in concentric circles. The direction of the magnetic field is found by a righthand rule.
  • Similarly, loops of wire that carry current create magnetic fields. The direction of the magnetic field is, again, found by a right-hand rule.
  • A magnetic field exerts a force on a charged particle if that particle is moving perpendicular to the magnetic field.
  • When a charged particle moves perpendicular to a magnetic field, it ends up going in circles. This phenomenon is the basis behind mass spectrometry.
  • A changing magnetic flux creates an induced EMF, which causes current to flow in a wire.
  • Lenz's Law says that when a changing magnetic flux induces a current, the direction of that current will be such that the magnetic field it induces is pointed in the opposite direction of the original change in magnetic flux.
  • The Biot–Savart law has as its consequence that a little element of wire carrying a current produces a magnetic field that (1) wraps around the current element via the right-hand rule, and (2) decreases in magnitude as 1/r2, r being the distance from the current element.
  • Ampére's law has as its consequence that (1) the magnetic field produced by a very long, straight current is
  • outside the wire; inside the wire, the field increases linearly from zero at the wire's center, and (2) the magnetic field produced by a wire-wrapped torus is zero everywhere outside the torus, but nonzero within the torus. The direction of the field inside the torus is around the donut.

  • An inductor resists the change of current in a circuit. In an RL circuit, when the battery is first connected, the current increases asymptotically from zero up to a final value of V/R. When the battery is disconnected, the current decreases asymptotically to zero. In an LC circuit, the charge on the capacitor oscillates from maximum to minimum sinusoidally with period .
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