©
COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON
I, PART B 1.8.1.5
Different materials vary in their ability
to transfer electrons. Substances, such as wood
and rubber, have what is called a tight electron bond and their atoms greatly
resist the free
movement of electrons. Such materials are considered poor electrical conductors.
Metals, on the other hand, have large
amounts of electrons that transfer freely. Their comparatively
low electrical resistance classifies them as good electrical conductors.
1.8.1.6 Electrical
resistance is primarily due to the reluctance of atoms to give up their
electron particles. It may also
be thought of as the resistance to current flow. 1.8.1.7
To better understand the electrical
terms discussed above, we might compare the
closed water system with the electrical diagram shown in Figure 8. You can
see that as the
pump is running, the water will move in the direction of the arrows. It
moves because pressure
has been produced and that pressure can be likened to voltage in an electrical
circuit. The pump can be compared
to a battery or a DC generator. The water flows through
the system at a certain rate. This flow rate in an electrical circuit is
a unit of measure
known as the ampere. The small pipe in the fluid circuit restricts the flow
rate and can be
likened to a resistor. This unit resistance is known as the ohm. If
we close the valve
in the fluid circuit, we stop the flow, and this can be compared to opening a
switch in an electrical
circuit. 1.8.2
Ohm's
Law -
Resistance is basic to electrical theory and to understand this
principle, we must know the Ohm's Law,
which is stated as follows: In any electrical circuit,
the current flow in amperes is directly
proportional to the circuit voltage applied and in- versely
proportional to the circuit resistance. Directly proportional means that
even though the
voltage and amperage may change, the ratio of their relationship will not. For
example, if we
have a circuit of one volt and three amps, we say the ratio is one to three. Now
if we increase
the volts to three, our amperage will increase proportionately to nine amps. As
can be seen, even though the voltage
and amperage changed in numerical value, their ratio
did not. The term "inversely proportional" simply
means that if the resistance is FIGURE
8 VALVE
SWITCH RESISTOR
10 OHM BATTERY
12 VOLT ELECTRICAL
DIAGRAM SMALL
PIPE PUMP
CLOSED WATER SYSTEM
LARGE PIPE
