c. 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.

a. Amperes. Current flow, or electron flow, is

Other elements, such as iron, do not lose their electrons

measured in amperes. While it is normally considered

quite as easily, so there are fewer free electrons in an

iron wire (comparing it to a copper wire of the same

(approximately what a 100-watt light bulb would draw), it

size). Thus, with fewer free electrons, fewer electrons

is actually a tremendous flow of electrons. More than 6

can push through an iron wire; that is, the iron wire has

billion billion electrons a second are required to make up

more resistance than the copper wire.

one ampere.

d. A small wire (in thickness or cross-sectional

b. Voltage. Electrons are caused to flow by a

area) offers more resistance than a large wire. in the

difference in electron balance in a circuit; that is, when

small wire, there are fewer free electrons (because fewer

there are more electrons in one part of a circuit than in

atoms), and thus fewer electrons can push through.

another, the electrons move from the area where they

are concentrated to the area where they are lacking.

e. Most metals show an increase in resistance with

This difference in electron concentration is called

an increase in temperature, while most nonmetals show

potential difference, or voltage. The higher the voltage

a decrease in resistance with an increase in

goes, the greater the electron imbalance becomes. The

temperature. For example, glass (a nonmetal) is an

greater this electron imbalance, the harder the push on

excellent insulator at room temperature but is a very poor

the electrons (more electrons repelling each other) and

insulator when heated to red heat.

the greater the current of electrons in the circuit. When

there are many electrons concentrated at the negative

terminal of a generator (with a corresponding lack of

electrons at the positive terminal), there is a much

a.

stronger repelling force on the electrons and,

The general statements about voltage,

consequently, many more electrons moving in the wire.

amperage, and ohms (para 11-9 and 11-10) can all be

This is exactly the same as saying that the higher the

related in a statement known as ohm's law, so named for

voltage, the more electric current will flow in a circuit, all

the scientist Georg Simon Ohm who first stated the

other things, such as resistance (para 11-10), being

relationship. This law says that voltage is equal to

equal.

amperage times ohms. Or, it can be stated as the

mathematical formula:

E=IxR

a.

Even though a copper wire will conduct

where E is volts, I is current in amperes, and R is

electricity with relative ease, it still offers resistance to

resistance in ohms.

For the purpose of solving

electron flow. This resistance is caused by the energy

problems, the ohms law formula can be expressed three

necessary to break the outer shell electrons free, and the

ways:

collisions between the atoms of the conductor and the

free electrons. It takes force (or voltage) to overcome

(1) To find voltage: E = IR

the resistance encountered by the flowing electrons.

This resistance is expressed in units called ohms. The

(2) To find amperage: l = E/R

resistance of a conductor varies with its length, cross-

sectional area, composition, and temperature.

(3) To find ohms: R = E/I

b. A long wire offers more resistance than a short

b. This formula is a valuable one to remember

wire of the same cross-sectional area. The electrons

because it makes understandable many of the things

have farther to travel.

that happen in an electric circuit. For instance, if the

voltage remains constant, the