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).