The role of a resistor in a circuit

Resistor is made of some materials which hinder the current. It is one of the most basic and commonly used electronic components. Resistor has many uses in the circuit, which can be summarized as reducing voltage, distributing voltage, limiting current and providing necessary working conditions (voltage or current) to various components. For convenience of expression, resistor is usually referred to as resistance.

In order to adapt to different needs, the state has stipulated a series of resistance values as the product standards, and clearly marked the standard resistance values on the products, which is called the nominal resistance. The nominal resistance series of Chinese resistors are shown in Table 2-1. Than given in the table base, can be multiplied by 10. 100. 1000-3.9 the base, for example, can be 3.9 Ω, can also be a 39 Ω, 390 Ω, 3.9 k Ω Ω Ω, 39 k, 390 k and 3.9 M Ω, etc.

However, the nominal resistance value is not 100% equal to the actual resistance of the resistor due to the error in the production process. The difference between the actual and nominal resistors, often expressed as a percentage of the difference and the nominal resistors, is called the allowable deviation (or resistance error). Resistor products can be divided into three grades according to the allowable deviation, that is, the allowable deviation of grade I is ±5%; Deviation of plus or minus 10% allowed Ⅱ level; Ⅲ magnitude deviation of plus or minus 20% allowed. It is obvious that the smaller the allowable deviation is, the more accurate the resistor is. A resistor is an energy-consuming device. When an electric current passes through the resistor, some of the electrical energy is converted into heat, raising the resistor's temperature. The resistor can be damaged by overheating if it is used with too much current or at too high a voltage at both ends. Therefore, various resistors specify their nominal power (also known as power rating). If the resistor is used below the rated power, it will have a long life and work safely. If overworked, the lighter can shorten its service life, while the heavier may burn out the resistor. The maximum electrical power the resistor is allowed to withstand for a long period of time is rated power in watts (W). Generally, resistors are divided into 1/16W, 1/8W, 1/4W, 1/2W, 1W, 2W, 5W, 10W, etc. The actual power consumed by resistors in use must be less than its rated power. In electronic fabrication, 1/8W or 1/4W resistors are usually used if they are not specified in the circuit.