BASIC ELECTRONICS - OD1633 - LESSON 1/TASK 1
Some elements can lose electrons more readily than other elements. Copper
loses electrons easily, so there are always many free electrons in a copper
wire. Other elements, such as iron, do not lose their electrons quite as
easily, so there are fewer free electrons in an iron wire (comparing it to a
copper wire of the same size).
Thus, with fewer free electrons, fewer
electrons can push through an iron wire; that is, the iron wire has a higher
resistance than the copper wire.
A small wire (in thickness or cross-sectional area) offers more resistance
than a large wire.
In the small wire, there are fewer free electrons
(because fewer atoms), and thus fewer electrons can push through.
Most metals show an increased resistance with an increase in
temperature,
while most nonmetals show a decrease in resistance with an
increase in
temperature. For example, glass (a nonmetal) is an excellent
insulator at
room temperature but is a very poor insulator when heated to
the point of
becoming red.
In the next paragraphs, voltage, current, and resistance will be applied to
Ohm's law.
5.
Ohm's Law
a. Defining Ohm's Law. The general statements about voltage, current,
and resistance can all be related in a statement known as Ohm's law, named
for the scientist George Simon Ohm, who first stated that relationship.
This law says that voltage is equal to amperage times Ohms. Or, it can be
stated as the mathematical formula:
E=IxR
where E is voltage in volts, I is current in amperes, and R is resistance in
Ohms.
For the purpose of solving problems, the Ohm's law formula can be
expressed three ways:
o
To find voltage:
E=IxR
o
To find amperage:
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