The purpose of a bifilar coil, usually called a bifilar winding, is to provide electrical resistance. Bifilar winding is a term for a coil with two closely spaced, parallel-wound wires. Manufacturers use bifilar windings to make electronic components called resistors.
Resistors are a common component in modern electronic circuitry, and they are used for a variety of purposes, such as producing heat and regulating voltage. They are made of various materials, such as copper, nickel, tungsten and iron. Some resistors contain non-metallic materials including ceramic and carbon.
Resistors apply an opposing force, or resistance, on electrical current. The opposing force produced by a resistor can produce energy or limit the flow of electrical current. Some common uses for resistors are the heating elements in a toaster and the light filament in a light bulb.
The resistance and tolerance level of a resistor determine how it can be used. The unit of measure for resistance, also called impedance, is ohms. Tolerance is a measure of the variance in resistance and is expressed as a positive and negative percentage. Manufacturers use a color coding scheme to display a resistor's ohms and tolerance. The color scheme consists of three bands of color for ohms and a fourth band for tolerance. Engineers use the tolerance and ohms figures to determine the maximum or minimum impedance of the resistor.