Low power resistors are usually made of carbon film encapsulated in a plastic shell, while high-power resistors are usually wound resistors, which are made by winding metal wires with high resistivity around the porcelain core.
If the resistance value of a resistor is close to zero ohms (for example, a large cross-section wire between two points), the resistor has no blocking effect on the current. The circuit in parallel with this resistor is short circuited and the current is infinite. If a resistor has infinite or large resistance, the circuit connected in series with the resistor can be regarded as an open circuit with zero current. The resistor commonly used in industry is between the two extreme cases. It has a certain resistance and can pass a certain current, but the current is not as large as when it is short circuited. The current limiting effect of the resistor is similar to that of the small-diameter pipe connected between two large-diameter pipes to limit the water flow. Resistance, the English name of resistance, usually abbreviated as R, is a basic property of conductor, which is related to the size, material and temperature of conductor. Ohm's law says that i=u/r, then r=u/i, the basic unit of resistance is Ohm, which is represented by the Greek letter "Ω". There is such a definition: when a voltage of one volt is added to a conductor, the resistance corresponding to one ampere current is generated. The main function of resistance is to block the flow of current. In fact, "resistance" refers to a kind of property, and the resistance usually referred to in electronic products refers to such an element as a resistor. Ohm is often abbreviated as ohm. The commonly used units of resistance are kilo ohm (K Ω), megaohm (m Ω), and milliohm (m Ω)