What is the measure of resistance?
Immediately mention that it will be a question of measuring the resistance to electric current. What is it, and what is the measure of resistance?
Three whales
Where does this resistance come from? All materials in nature, in terms of electrical conductivity, are divided into 3 categories - insulators, semiconductors, and conductors. The former do not conduct an electric current at all (for example, glass, plastic, air), the latter - let the current flow only under certain conditions (silicon, germanium), and all modern electronics are built on their basis. But we are interested in the last - all familiar guides. Ordinary copper wire, the wire that connects your computer to the outlet - all are conductors.
How can conductors resistelectric current? The fact is that there is no ideal conductor in nature. In any, even the most "pure" conductor, there is always some of the impurities that resist the electrons moving in the body of the conductor. The collision of electrons with these impurities causes heating, and sometimes (if the flux density is too high, i.e. too high current) and the destruction of the conductor (this is the basis of the action of heating elements and fuses).
Some math
What is the resistance of the conductor, orOr rather, the electric circuit? The unit of measurement of this magnitude is named after the physicist Georg Simon Oma. Yes, the same Om, whose law we all taught at school. In the technical literature is designated by the letter "omega". The resistance in the calculations is written as "R" (U - voltage, I - current, P - power, etc.). What does this magnitude mean? Let's consider an example. According to the law of the same Ohm, if our conductor has a resistance of 1 Ohm, applying a voltage of 220 volts to its ends, we will get a current (current = voltage divided by the resistance) of 220 amperes. Multiplying the current by the voltage, we know the power: 220 volts * 220 amps = 48400 watts, or 48 kilowatts. This is VERY big power, which no household wiring can withstand. In fact, such a current will be a short-circuit current. This shows how important it is to know exactly the resistance of the circuit before applying voltage! Fortunately, it is not so difficult to learn it, and it is not even necessary to make some calculations. There are special measuring instruments - ohmmeters, which show the magnitude of the resistance to direct current. Their type of megohmmeter is designed to measure large values of resistances, and are used primarily for insulation testing. Now it is difficult to meet ohmmeters as separate devices. For the most part, they are part of the combined instruments - the avometers, or multimeters, which are sold in every Chinese goods stall.
So, successful measurements to you!
