# Basic knowledge of electronics – resistance

1. Definition and function of resistance

In ORDER TO CONTROL THE VOLTAGE AND current IN a CIRCUIT, that is, to reduce the voltage and limit the current, a component with a certain numerical resistance is needed. This component is called a resistor, or resistor for short.

2. Unit of resistance: ohms (ω), thousands of ohms (Kω), megaohms (Mω)

Unit conversion: 1 megohm (Mω)= 103 Kω = 106 ohms (ω)

3. The expression of resistance: 4. Type of resistance

Note: Now many commonly used SMT digital resistance code for 103, 3002, etc.

Its conversion method is as follows:

② Four-digit numerical resistance:

In general, the three-position resistance is the ordinary resistance, and the four-position resistance is the exact resistance.

Four-color ring resistance (common color ring resistance)

5 color ring resistance (precision color ring resistance)

The first, second and third color rings are significant digits, then 425; the fourth color ring is the square degree of 10, then it is the first power of 10; the fifth color ring is the error

So: 425×10=4250 ω

Error of plus or minus 1%

⑤ thermistor

The resistance value varies with temperature (within the critical value).

⑥ Varistor

The resistance value varies with the applied voltage (within the critical value).

⑦ Other resistors

Photoresistor: The resistance value of the resistor varies with the ambient light level (within the critical value). As in street lights.

Gas sensitive resistor: The resistance value of a resistor varies with the content of a particular gas (within the critical value). For example: harmful gas detector.

Adjustable resistance: The resistance value of the resistance changes with the slide position (within the maximum value of the resistance).

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