FIG. 28–WHEN A MAGNET IS THRUST INTO A COIL OF WIRE IT CAUSES A CURRENT TO FLOW IN THE COIL, BUT THE CURRENT FLOWS ONLY WHILE THE MAGNET IS MOVING
Drawing reproduced by permission of Joseph G. Branch.
A friend of Faraday, on learning of this discovery, wrote the following impromptu lines:
"Around the magnet Faraday
Was sure that Volta's lightnings play.
But how to draw them from the wire?
He took a lesson from the heart:
'Tis when we meet, 'tis when we part,
Breaks forth the electric fire."
A magnet will produce an electric current in a wire, but only when the magnet or the wire is in motion.
Detecting and Measuring an Electric Current
The instrument which Faraday used to detect a current was derived from Oersted's experiment. When a current flows in a north-and-south direction over a compass-needle, the needle swings round. When the current stops flowing the needle swings back to the north-and-south position. The effect on the needle is stronger if the current flows through a coil of wire and the coil is placed in a north-and-south position around the needle (Fig. 29). The stronger the current flowing through the coil the farther the needle will turn from the north-and-south position.
