Induced EMF:
Induced EMF for a rectangular wire moving into or out of a magnetic field:
ε = BLvTime constant for an LR circuit:
When most people think of magnets, they imagine horseshoe-shaped objects that can pick up bits of metal.
Or maybe they visualize a refrigerator door. But not a physics ace like you! You know that magnetism is a
wildly diverse topic, involving everything from bar magnets to metal coils to mass spectrometers.
Perhaps you also know that magnetism is a subject filled with countless “right-hand rules,” many of which
can seem difficult to use or just downright confusing. So our goal in this chapter—besides reviewing all
of the essential concepts and formulas that pertain to magnetism—is to give you a set of easy-to-
understand, easy-to-use right-hand rules that are guaranteed to earn you points on the AP exam.
Magnetic Fields
All magnets are dipoles, which means that they have two “poles,” or ends. One is called the north pole,
and the other is the south pole. Opposite poles attract, and like poles repel.
You can never create a magnet with just a north pole or just a south pole. If you took the magnet in
Figure 20.1
Figure 20.1 Bar magnet.and cut it down the middle, you would not separate the poles. Instead, you would create two magnets like
those shown in Figure 20.2 .
Figure 20.2 Cutting the bar magnet in Figure 20.1 in half just gives you two smaller bar magnets.
You can never get an isolated north or south pole.