Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1890-11-02
SOME SIMPLE TERMS
That Are Now in Everyday Use, but
Are Little Understood.
HINTS USED BY ELECTRICIANS.
Explanations Which Will Enable One to
Talk Intelligently Of
VOLTS, AMpEREs, oHMs AND WATTS
WRITTEN FOB THE DISPATCH,

such expressions must be very puZzling to
the layman. However, they are not nearly
as mysterious as they sound. Familiarity
and use is all that is needed to make these
expressions just as Ineligible as the foot,
yard or quart. Comparatively few people
know how many feet there are in a mile,
and there are not few people that would
get but faint idea from the expression 800
feet high. Yet all are perfectly familiar
with the terms foot, yard or quart, and are
capable of using them intelligently in gen.
eral conversation and for all ordinary pur-
poses. ..
And now, in these days of electricity,
when electrical topics are constantly before
the public and electrics currents in every
city, it seems high time that people in gen.
eral should shake of an indescribable
dread, sort of shrinking feeling about the
electric current as though it were some
monster or supernatural being, and become
familiar with this new and wonderful agent,
ever ready to do our bidding.
THE FOUR UNITS.
Electricity is form of energy, and,
natural enough, like all other forms OF
energy, such as steam, water power, gun
powder, etc., can do much mischief
when improperly handled. But when in.
telligently and rightly used it is one of the
most easily applied and flexible forms of
energy known. Let us then help and not
hinder its progress in the industries, and the
best way to overcome this almost universal
shrinking from it Is to become familiar with
it and learn to appropriate its many good
qualities. Now, one of the best ways to be-
gin this ia to obtain clear idea Of its prin-
cipal units of measurements.
Electrical units have been given proper
names. Ampere, Watt, etc., are the names
OF men who have made themselves famous
in this electrical branch of science. But in
themselves these names mean nothing more
than do the expressions foot or pound. The
four most commonly used electrical units
are the volt, or unit of pressure, the ampere.
or unit of quantity of current, the ohm, or
unit of resistance, and the watt, or unit of
energy. This last unit is always the
product of the pressure into the quantity of
current and Is often called the volt-ampere.
However, the expression watt is preferable,
being shorter, and, in fact, volt-ampere is
fast going out of use.
The best way TO make first acquaintance
with these units is to compare and liken
them, as far as possible, with units already.
The volt or unit of pressure corresponds to
the unit fnot when used in the sense of pres
sure. When we speak of hundred feet of
pressure in water pipe we know that the
level of the water in the reservoir is 100
feet above the pipe in question-and We un-
derstand the expression 100 feet of pressure
because we are familiar with it and know
THE GENERAL EFFECT
that can be obtained from that pressure.
For example, we know that if a hole is
made in the pipe, stream of water will,
except for friction, rise 100 feet high. In
the same way, anybody would make pretty
good guess as to how many pounds there are
in one cubic foot of water, and this is only
because we are familiar with those units of
measure, and not because we know anything
about their history or why they were given
| such names.
In electricity the relation of the units
above mentioned is beautifully simple, and
| is called Ohm's law, Ohm being the name of
the man that discovered the law, which is
this: ''The pressure is equal to the quantity
multiplied by the resistance" That is, the
volts always equal the product of the
ampere into the ohms. To that-if we rep
resent the volts by V, ampere by A and
ohms by Owe have these three simple
| equations: V equals A multiplied bv o, A
| equals V divided by o and o equals V divided
by A, from which, if any two OF the three
| quantities are known, the third can always
| be calculated.
For example, if we have V "A and A .,
then y will equal 2, because - VA =
AZ q. aud so on.
There is one other term to consider. and
| that is the watt or unit OF work (energy)
If we represent this by W, we have this
| very simple law: WV A. That is, 6
watts are equal to volts times ampere, or
3 volts times 2 ampares, or 2 volts times
amperes. Now, it takes TAG watts to equal
one horse power of energy, so that. if we
| have amperes flowing under a pressure of
| 1913 volts, we will be able to do the work of
one horse power with the current, for here
v 373 and A ., and so from W WA
we have v 373 q 746 watts or one
! horse power.
1t will thus be seen how very simple il is
TO talk intelligently about the power of an
electric current For example, il q man
says he has an electric current doing a work
of ten-horse power under pressure of 1000
volts, we at once know that he is using q
current of 7.46 amperes, because ten-horse
power equals 7, 460 watts, and this equals
1000 volts times TAG amperes. In fact,
energy in electric power is measured in very
| much the same way that it is in water
power.
| THE ELEMENT OF TIME.
| With water the energy is measured by the
product of the pressure into the quantity of
water flowing in given time. When we
say that 746 watts equals one horse power,
| we mean the effort of one horse power; but
| if we wish to estimate the work that can be
done with given number of watts, the ele-
ment of time must be taken into consider
alton. And so we speak of Watt-hours or
| borse-poye hours that is 746 watts will do
in one hour the same work that one horse
power from a steam engine will do in one
| hour, Also one watt will do in 746 hours
| the same work that TAG watts will do in one
| hour.
Some examples now of common uses of
the electric current may be Of assistance In
familiarizing one with thu units that we
have Just been considering. Let us imagine
an electric circuit having 20 arc lamps in
series, that is, one after tie other, and let us
assume further that this dynamo furnishes q
pressure of 1000 volts and current OF 1O
amperes Now, neglecting the resistance of
the wire, we can easily figure from Ohm's
law the electrical resistance of each lamp,
thus: O=V-A - 1,0OO-10 - 100 ohms.
That is, the resistance OF all the 20 lamps in
series is 100 ohms. Therefore one lamp has
resistance of 100-20 % ohms. If each
lamp has ohms resistance we can find how
much pressure is needed to force the current
of 10 amperes through one lamp, by
v=O Z A =5x 10 = 30 volts.
PROVING THE FIGURES.
To prove that this is correct we can de-
termine the pressure for one lamp in the
following way: We have 1000 volts to
force the current through 20 lamps, there
fore it will take 1,000-20=50 volts to force
| 81. lara h.