Some elements can lose electrons more readily than other elements. 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: