440. Laws of Induction. (1) An increase in the number of lines of force that pass through a closed circuit produces an indirect induced current; while a decrease produces a direct one. (See [§ 428].)
(2) The E. M. F. of the induced current is equal to the rate of increase or decrease in the number of lines of force that pass through the circuit.
(3) A constant current produces no induced current, provided there is no motion.
(4) Closing a circuit produces an indirect current.
(5) Opening a circuit produces a direct current.
(6) Lenz's Law. Induced currents have a direction that tends to stop the motion that produces them.
441. Primary and Secondary Currents. In the preceding experiments in induction, it must be kept in mind that the current from the cell did not pass through the galvanoscope. There were two entirely separate circuits,[185] in no way connected. The primary current comes from the cell, while the secondary current is an induced one.
EXPERIMENT 182. To see what is meant by alternating currents.