Honolulu star-bulletin. [volume] (Honolulu [Oahu, Hawaii]) 1912-2010, 1916-10-07

er the current of water through the
pump the greater the pressure re-
quired to overcome the internal re-
sistance of the pump
When there is no current through
the pump the difference into the pres
sures indicated by two gauges con-
nected to the terminals of the pumps
will represent the total pressure pro-.
duced by the pump. The part of this
total pressure which is available to
act on the external circuit and pro-
duces a current will depend upon how
much Of it is used within the pump it.
self. It is obvious that the pressure
between the terminals of the pump
when there is q certain current
through 1t will be greater for low
internal resistance than for a high in
ternal resistance. Hence it is desir-
able to have the internal resistance of
the pump as low as possible in order
that just as much of the pressure it
produces be available at the terminals
of the pump. The pressure between
the terminals of the pump viii
change as the current through the
pump changes, even though the total
pressure produced by the pump re-
mains constant The larger the cur
rent in the pump the lower the differ
ence between the terminal pressures.
All of the pressure produced by the
battery or generator is not available
at the terminals, as part of the pres
sure is used in causing the electricity
to flow through generator or battery.
The opposition offered by the genera
tor or battery TO the flow of the cleo
tricity through it is called the internal
resistance. The action of the internal
resistance of the generator or battery
is exactly the same as the internal re-
sistance of the pump. 1t results in the
pressure between the terminals of the
generator or battery, decreasing as
the value of the current through them
Increases, assuming the total pressure
generated remains practically con-
stant A few simple examples will per-
haps give the reader a better under
standing of the effect of this internal
resistance upon the operation of the
electrical circuit.
Internal Resistance of Battery
The total pressure generated in a
certain storage battery is 6.S volts and
the internal resistance of the battery,
is .04 ohm. What will be the pressure
between the terminals of the battery
when the battery is supplying a cur
rent of 20 amperes?
The pressure required to produce
current of 20 amperes through a re-
sistance of .04 ohm is equal to the
product of the current and the resist
ance. .04x20, or 8 volt. The pressure
available at the terminals of the bat
terry will be equal to the total pres
sure minus the pressure required to
produce the current through the inter
nal resistance, or 6.8 minus 8, or 6
volts. :..:.
If several batteries similar to the
above be connected in series so that
their pressures are all acting in the
same direction around the circuit
there will be a decrease in the value
of the pressure between the termin-
ais or each of the batteries as the cur
rent in the circuit increases in value
The decrease in pressure of the diff
ferent batteries will be the same pro-
vided their internal resistances are
equal in value If the internal resist
ance Of the different batteries is not
equal there will be greater decrease
in the value of the pressure between
the terminals of the batteries of larg-
er internal resistance than between
the terminals of the batteries of lower
internal resistance. ~
1t may happen that the internal re-
= -
les is such that the pressure required
to cause the electricity to flow
through its internal resistance is