A Test of the Preceding Statement
How Electricity is obtained on a Large Scale
We will test the statement that a magnet has electric properties by another experiment. Between the poles of a strong magnet suspend a movable coil which is connected with a sensitive galvanometer. Starting with the coil in the position of Figure 228, when many lines of force pass through it, let the coil be rotated quickly until it reaches the position indicated in Figure, when no lines of force pass through it. During the motion of the coil, a strong deflection of the galvanometer is observed; but the deflection ceases as soon as the coil ceases to rotate. If, now, starting with the position of Figure 238, the coil is rotated forward to its starting point, a deflection occurs in the opposite direction, showing that a current is present, but that it flows in the opposite direction. So long as the coil is in motion, it is cut by a varying number of lines of force, and current is induced in the coil. The above arrangement is a dynamo in miniature
. By rotation of a coil (armature) within a magnetic field, that is, between the poles of a magnet, current is obtained.
In the motor
, current produces motion. In the dynamo
, motion produces current.
FIG. - As long as the coil rotates between the poles of the magnet, current flows.