如果一个电阻器的电阻值接近零欧姆（例如，两个点之间的大截面导线），则该电阻器对电流没有阻碍作用，并联这种电阻器的回路被短路，电流无限大。如果一个电阻器具有无限大的或很大的电阻，则串接该电阻器的回路可看作开路，电流为零。工业中常用的电阻器介于两种情况之间，它具有一定的电阻，可通过一定的电流，但电流不像短路时那样大。电阻器的限流作用类似于接在两根大直径管子之间的小直径管子限制水流量的作用。电阻，英文名resistance，通常缩写为R，它是导体的一种基本性质，与导体的尺寸、材料、温度有关。欧姆定律说，I=U/R，那么R=U/I，电阻的基本单位是欧姆，用希腊字母“Ω”表示，有这样的定义：导体上加上一伏特电压时，产生一安培电流所对应的阻值。电阻的主要职能就是阻碍电流流过。事实上，“电阻”说的是一种性质，而通常在电子产品中所指的电阻，是指电阻器这样一种元件。欧姆常简称为欧。表示电阻阻值的常用单位还有千欧（kΩ），兆欧（MΩ），毫欧（m Ω）。
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)
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