FIGURE 14. INDUCTOR TYPES AND SCHEMATIC SYMBOLS.

turns in the coil, the diameter of the coil, the coil length,

the type of material used in the core, and the number of layers

of windings in the coil.

(a) *Number of Turns in a Coil*. Inductance depends entirely

upon the physical construction of the circuit, and can only be

measured with special laboratory instruments. Of the factors

mentioned, consider first how the number of turns affects the

inductance of a coil. Figure 15 on the following page shows two

coils. Coil (A) has two turns and coil (B) has four turns. In

coil (A), the flux field set up by one loop cuts one other loop.

In coil (B), the flux field set up by one loop cuts three other

loops. Doubling the number of turns in the coil will produce a

field twice as strong; cutting twice the number of turns will

induce four times the voltage. Therefore, it can be said that

the inductance varies as the square of the number of turns.