©
COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON
I, PART B doubled,
the current will be reduced to one-half. Ohm's Law can be stated mathematically
with this equation:
I = E ÷ R
or E
= I × R or
R = E ÷ I
(E
= Volts, I = Amperes, R = Resistance (Ohms)) 1.8.2.1
The equation is easy to use as seen
in the following problems: 1)
A 12 volt battery has a built-in resistance
of 10 ohms. What is the amperage? 12
÷ 10 = 1.2 amps 2)
What voltage is required to pass 15
amps through a resistor of 5 ohms? 15
× 5 = 75 volts 3)
When the voltage is 80 and the circuit
is limited to 250 amps, what is the value of
the resistor? 80
÷ 250 = .32 ohms 1.8.2.2
The theory of electrical resistance
is of great importance in the arc welding process
for it is this resistance in the air space between the electrode and the base
metal that contributes
to the transfer of electrical energy to heat energy. As voltage forces the
electrons to move faster, the energy
they generate is partially used to overcome the resistance
created by the arc gap. This energy becomes evident as heat. In the
welding process,
the temperature increases to the point where it brings metals to a molten state.
1.8.3
Electrical
Power - The word "watt"
is another term frequently encountered in electrical
terminology. When we pay our electrical bills, we are actually paying for
the power to run
our electrical appliances, and the watt is a unit of power. It is defined
as the amount
of power required to maintain a current of one ampere at a pressure of one volt.
The circuit voltage that comes into
your home is a constant factor, but the amperage drawn from
the utility company depends on the number of watts required to run the electrical
appliance. The watt is figured
as a product of volts times amperes and is stated math- ematically
with the following equation: W =E
× I E
= W ÷ I I
= W ÷ E (W
= Watts, E = Volts, I = Amperes) 1.8.3.1
The amperage used by an electrical
device can be calculated by dividing the watts
rating of the device by the primary voltage for which it is designed.
