CHAPTER XXXIV

HOW ELECTRICITY MAY BE MEASURED


312. Danger of an Oversupply of Current. If a small toy motor is
connected with one cell, it rotates slowly; if connected with two
cells, it rotates more rapidly, and in general, the greater the number
of cells used, the stronger will be the action of the motor. But it is
possible to send too strong a current through our wire, thereby
interfering with all motion and destroying the motor. We have seen in
Section 288 that the amount of current which can safely flow through a
wire depends upon the thickness of the wire. A strong current sent
through a fine wire has its electrical energy transformed largely into
heat; and if the current is very strong, the heat developed may be
sufficient to burn off the insulation and melt the wire itself. This
is true not only of motors, but of all electric machinery in which
there are current-bearing wires. The current should not be greater
than the wires can carry, otherwise too much heat will be developed
and damage will be done to instruments and surroundings.

The current sent through our electric stoves and irons should be
strong enough to heat the coils, but not strong enough to melt them.
If the current sent through our electric light wires is too great for
the capacity of the wires, the heat developed will injure the wires
and may cause disastrous results. The overloading of wires is