Honolulu star-bulletin. [volume] (Honolulu [Oahu, Hawaii]) 1912-2010, 1916-12-23
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EEcIRoMAGNEnc TERMS ACTIONS EXPLAINED EXPERTS

Age).
Solenoids carrying current exhibit
all the magnetic effects that are pos
sessed by permanent magnets. They
attract and repel magnets, pieces OF
wire, and steel, other solenoids in
which is a current, etc. The magnet
lines pass through the solenoid from
the south pole to the north pole, ano
outside the solenold from the north
pole TO the south pole, just as in a
permanent magnet.
A simple rule by which the polarity
of a solenoid may be determined, If
the direction of the current in the
winding is known, is as follows: II
you face one end Of the solenoid and
the current is around the winding in
a clockwise direction, the end Of the
solenoid nearest you will be the south
pole and the other end will be the
north pole II the direction OF the
current in the winding is counter
rlockwise the end nearest you will
be the north pole and the other end
the south pole.
Another simple rule for determining
the polarity of solenoid is as fol.
lows: Grasp the solenoid with the
right hand. placing the fingers around
II in the direction of the current; the
thumb will then point In the direction
OF the north pole, as shown In figure l..
When current OF electricity is pro.
duced In the winding of solenoid il
becomes magnetized and lines of force
pass through the interior from the
south to the north pole and return
outside from the north to the south
pole. The current produces q force
which drives the lines of force, called
magnetic flux, through the paths
which they take, called the magnetic
circuit, just as the electromotive mo-
tive force in the electrical circuit
causes the electricity TO flow through
the electrical circuit. Magnetic flux
is measured in unit called the max.
well, and one maxwell simply means
one ounce OF force. This force, due
10 the electrical current, is called mag
netomotiye force, and IL is usually
abbreviated to NJ. NJ. F.
The magnetomotive force of sole.
mold is directly proportioned to the
product OF the Number of turns in the
solenoidr and the current In amperes
and turns are carrying. II the number
Of turns n the winding OF the solenold
is represented by the letter N and the
current II the winding by the letter I,
then thet magetomotive force will be
greater or less as the product NxI is
greater or less. The product of the cur
rent and turns Is called the ampere.
force, and the same magnetomotiye
force Is obtained with current OF 900
amperes through ! turn, Is amperes
through 20 turns. l ampere through
500 turns, etc. In each of the above
cases the magnetomotive force Is 600
ampere-turns.
In making magnetic calculations,
magnetomotive force is usually meas
ured In unit called the gilbert. II
magnetomotive force is expressed in
ampere-turns IL may be expressed in
Rilberts by multiplying the ampere-
turns by 1856. Thus the magnetic
motive force of 2 amperes in the
winding of a solenoid of so turns. is
700 ampere-turns, or 1856 gilberts.
Reluctance
The magnetomotive force acting on
any magnetic circuit encounters a Ger.
tain opposition to the production of
magnetic lux, just as the electrical
pressure encounters a certain opposi-
ton In the electrical circuit to the pro.
auction OF an electrical current. The
opposition offered by the magnetic cir.
cult is called its reluctance, and IL is
represented by the letter s. The re-
Iuctance OF magnetic circuit depends
upon the material composing the mag.
netc circuit and upon the dimensions
OF the magnetic circuit. II varies d.
iectly as the length of the circuit. an
versely as the area of the circuit. ALI
ether conditions remaining constant
fuo inversely as a property of the
f'aterial called its permeability, which
VII be defined later, represented by
the symbol NJ. The unit in which re-
luctance is measured is called the
oersted.
PermeabiIi
Inc number OF lines of force pass
ING through each square centimeter or
ross sectional area Of the solenoid
Then there is a magnetic core in the
soienoid is called the field strength.
Inc unit in which the field strength
Is usually measured is the gauss, and
~ is equal to one line of force per
square centimeter. Field strength is
frequently expressed as so many gil
eerts. per centimeter; that is. II is
equal to the magnetomotive force act.
ing on mahgetic circuit divided by
me length of the circuit in cent?
Ileters. Field strength is represented
~ the letter H. Any one of the fol.
lowing equations may be used in de-
'ermIning the value of the field
strength:
total magnetic flux maxwells
area in So. eentimeters so. cent?
metoers.
This equation holds true for uni.