1. Definition
Resistance (symbol: R), that is, a resistance to current, unit: ohm (symbol: Ω), which can be roughly divided into fixed resistance and variable resistance.
Its uses are mainly reflected in current limiting, voltage division, load, feedback, etc.
Two, characteristics
The use of multiple resistors can be in the following two situations: 1. Parallel connection. Second, in series.
1> Connect multiple resistors in parallel
When multiple resistors are connected in parallel, we regard it as a decrease in the overall resistance value. To give an example: suppose there are two bridges on a straight and wide road that are only for the width of a single vehicle. We think that its "only For a single vehicle width" that limits the passage of current, so here we regard the bridge as a resistor, and the two bridges are connected in parallel, because the two bridges have the same resistance value, but they are passing current at the same time, so in fact the current they pass (vehicles) are more than a single bridge, that is, the blocking effect is reduced.
The formula for calculating the resistance value of parallel resistors is:
When the resistors are connected in parallel , equal pressure shunts, that is, the voltages are equal, and the currents are divided according to the resistance ratio.
2> Multiple resistors in series
When multiple resistors are connected in series, we regard it as an increase in the overall resistance, and still use the above example: we regard it as two bridges connected in series on the same road, when the first bridge acts as a hindrance, the second bridge It will still continue to hinder the passage of vehicles, so the hindering effect is increased.
The formula for calculating the resistance value of a series resistor is:
When the resistors are connected in series , the voltage is divided and the current is equal, that is, the current is equal, and the voltage is divided according to the resistance ratio.
3. Calculation of wire resistance
In actual use, if the wire is short, its resistance can often be ignored, but in some large circuits, we need to consider the resistance of the wire.
Wire resistance formula:
The symbol ρ is the density of the material. Compared with other materials, copper material has lower resistance.
The symbol l is the length of the wire.
The symbol S is the cross-sectional area, and the calculation formula is [mm]².
Fourth, the resistance value identification
Here we will not repeat the identification of the resistance value in the circuit diagram, and turn to the identification of physical components.
First let's look at the common types of resistors:
Resistors play a very important role in the circuit. Among the above types, carbon film resistors are more common, which can also be divided into common four-ring resistors and five-ring resistors. The ring is the numerical digit, while the fifth ring is the numerical digit. Instead of reading the color ring to identify the resistance value, the most convenient way is to use a multimeter to type it faster.
5. Ohm's Law
official: