particular circuit. To find the power loss by this method, substitute the symbols I x R for
the symbol E in the power formula. This combination gives the formula P = I x I x R.
Thus, the power utilized in heat production is:
Power consumed = I2R (in watts)
where I is the current amperes and R is the resistance in ohms.
c. The portion of the circuit having the greatest resistance will produce the most
heat, and the power loss is proportional to the square of the amperage. If the current is
doubled, the power loss due to heat production is 22, or 4 times as great.
Section IV. MAGNETISM
CLASSIFICATION OF MAGNETS
A piece of metal that will attract bits of iron fillings is called a magnet. There are
three classes of magnets.
a. Natural Magnets. The earth possesses a natural magnetic field. Magnetite,
a natural magnet commonly referred to as lodestone, consists mainly of iron oxide and
is assumed to have become magnetized because of lying in the earth's magnetic field.
Natural magnets have very limited practical use because their magnetic force is very
weak and irregular.
b. Artificial Magnets. Artificial magnets are man-made and are produced in a
wide variety of shapes and sizes. They are constructed of hard steels or other special
alloys that are artificially magnetized. Such magnets are used extensively in electrical
equipment. They are classified as temporary or permanent. Their classification and
strength are determined by the material from which they are manufactured.
c. Electromagnets. Electromagnets depend upon an electric current for their
energy. They are usually temporary magnets that lose their magnetism when the
electric current is turned off. One of their big advantages is the ability to control both the
strength and duration of their magnetic force field.
2-10. PROPERTIES OF MAGNETS
a. Poles of a Magnet. Every magnet, regardless of shape, has two poles--the
north-seeking pole and the south-seeking pole. If a freely suspended magnet is
disturbed, it will return to north-south position and the north-seeking pole will always
point north. This is the principle on which the compass works.