f. *Power Loss in an Inductor*. Since an inductor (coil)

consists of a number of turns of wire, and since all wire has

some resistance, every inductor has a certain amount of

resistance. Normally this resistance is small. It is usually

neglected in solving various types of ac circuit problems

because the reactance of the inductor (the opposition to

alternating current, which will be discussed later) is so much

greater than the resistance that the resistance has a negligible

effect on the current.

(1) *Copper Loss*. However, since some inductors are designed

to carry relatively large amounts of current, considerable power

can be dissipated in the inductor even though the amount of

resistance in the inductor is small. This power is wasted power

and is called COPPER LOSS. The copper loss of an inductor can

be calculated by multiplying the square of the current in the

(2) *Iron Losses*. In addition to copper loss, an ironcore

coil (inductor) has two iron losses. These are called

HYSTERESIS LOSS and EDDYCURRENT LOSS. Hysteresis loss is due

to power that is consumed in reversing the magnetic field of the

inductor core each time the direction of current in the inductor

changes.

Eddycurrent loss is due to currents that are induced in the

iron core by the magnetic field around the turns of the coil.

These currents are called eddy currents and flow back and forth

in the iron core.

All these losses dissipate power in the form of heat. Since

this power cannot be returned to the electrical circuit, it is

lost power.

g. *Mutual Inductance*. Whenever two coils are located so that

the flux from one coil links with the turns of the other coil, a

change of flux in one coil causes an emf to be induced in the

other coil. This allows the energy from one coil to be

transferred or coupled to the other coil. The two coils are

said to be coupled or linked by the property of MUTUAL

INDUCTANCE. The amount of mutual inductance depends on the

relative positions of the two coils. This is shown in figure 22

on the following page. If the coils are separated a

considerable distance, the amount of