17.2. Ohm’s Law http://www.ck12.org
FIGURE 17.7
The red wire is now connected to the
negative terminal of the battery; the motor
runs in the opposite direction.hand, electrical wires are never “empty.” There is no such thing as a conducting wire that is empty of electrons
Our analogy can be continued, however, with friction. An electrical current, just as a flow of water, encounters
resistance. When potential difference is applied to the ends of a wire, electrons are compelled to move through the
wire. But their movement does not happen in an orderly fashion like a troop of marching soldiers. Their movement
is more like that of people running through a crowded train station. The effect produces an analogue to mechanical
friction called electrical resistance.
Ohm’s Law
It was a French physicist Georg Simon Ohm (1787-1854)Figure17.8, who first proposed that a currentIis directly
proportional to a potential difference (voltage)V→I∝Vfor metallic conductors, as long as the conductor does
not heat up too much. Otherwise, the relationship does not remain linear. Ohm’s law is, therefore, only applicable
if heating does not alter the characteristics of the circuit. In general, heating does have an effect on most circuits,
and thus Ohm’s law has a very limited range of usefulness.Ohm’s lawis not really a law, if by “law” we mean a
universally correct brief statement explaining a broad expanse of phenomena.
FIGURE 17.8
Georg Simon Ohm