Electric Circuits
Although static electricity has its useful applications, more useful by far is a
system that can continuously separate negative from positive charges, then extract
energy from them as they move around to recombine. This is the principle of the
electric circuit. Figure .1 shows a very simple electric circuit, consisting of a
battery with its two ends connected by a single wire.
system that can continuously separate negative from positive charges, then extract
energy from them as they move around to recombine. This is the principle of the
electric circuit. Figure .1 shows a very simple electric circuit, consisting of a
battery with its two ends connected by a single wire.
Figure 5.1. A very simple electric circuit, consisting of a battery with its two ends
connected by a metal wire. (Don’t try this at home unless you don’t mind running
down the battery very quickly.)
The battery uses chemical energy to separate negative from positive charges,
always maintaining a slight excess positive charge on its “+” end and a slightconductors, these excess charges just sit there and do nothing of interest. Connect
the two ends together with a metal wire, however, and the electrons will move along
the wire in order to recombine with the protons. Along the way, they will collide
with the atoms in the wire, creating a kind of “friction” that makes the wire get hot.
The battery, meanwhile, keeps replenishing the supply of electrons at its negative
end, until its internal chemical reaction has gone to completion. In summary, this
circuit converts chemical energy in the battery into electrical energy, which is then
converted into thermal energy in the wire.
always maintaining a slight excess positive charge on its “+” end and a slightconductors, these excess charges just sit there and do nothing of interest. Connect
the two ends together with a metal wire, however, and the electrons will move along
the wire in order to recombine with the protons. Along the way, they will collide
with the atoms in the wire, creating a kind of “friction” that makes the wire get hot.
The battery, meanwhile, keeps replenishing the supply of electrons at its negative
end, until its internal chemical reaction has gone to completion. In summary, this
circuit converts chemical energy in the battery into electrical energy, which is then
converted into thermal energy in the wire.
Figure2 shows a slightly more complicated circuit, consisting of a battery, a
pair of wires, and an ordinary incandescent light bulb. This circuit is essentially a
flashlight. Because the filament of the bulb offers significantly more resistance to
the flow of electrons than do the wires leading to it, the electrons will flow much
more slowly in this circuit than in the previous one. Instead of creating thermal
energy uniformly along the wires, this circuit concentrates the thermal energy at the
point of greatest resistance, the filament. The filament becomes so hot that it glows.
The bulb around the filament keeps oxygen out, preventing chemical reactions of the hot metal filament with oxygen.
pair of wires, and an ordinary incandescent light bulb. This circuit is essentially a
flashlight. Because the filament of the bulb offers significantly more resistance to
the flow of electrons than do the wires leading to it, the electrons will flow much
more slowly in this circuit than in the previous one. Instead of creating thermal
energy uniformly along the wires, this circuit concentrates the thermal energy at the
point of greatest resistance, the filament. The filament becomes so hot that it glows.
The bulb around the filament keeps oxygen out, preventing chemical reactions of the hot metal filament with oxygen.
Figure 2. A “flashlight” circuit, consisting of a battery connected to a light bulb
by a pair of wires. (The connections inside the bulb simply route the electric current
through the filament.)
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