http://www.ck12.org Chapter 19. Electromagnetism
the presence of electric current. It is, essentially, a very sensitive ammeter.) While the magnet is in motion, the
galvanometer detects a few microamperes of current in the loop of wire, first in one direction (right),Figure19.1,
and then in the other direction (left),Figure19.2.
FIGURE 19.1
Magnet moved toward loop.FIGURE 19.2
Magnet moved away from loop.Note the directions of the velocity vector (in red) of the magnet in both diagrams.
How do we explain these results?
When the magnet is movedtowardthe loop of wire, the number of magnet field lines passing through the loop
changes (the magnetic field changes), and a current is registered by the galvanometer. The current is called an
induced current. Notice that the direction of the galvanometer needle is to the right in theFigure19.1, and note
the direction of the induced current in the loop, as well!