How to find resistance

How to find resistance

It is the simplest to find chain resistance by means of an ohmmeter. However, not always this device is available. Besides, sometimes connection of an ohmmeter is just physically impossible. In these cases it is necessary to use alternative methods.

It is required to you

  • ohmmeter, voltmeter, ampermeter


1. To measure chain resistance, attach the device which is called an ohmmeter to the ends of the necessary site. On its scale or a digital board the value of resistance of this site of a chain will appear.

2. If there is no such device, measure resistance of the site of a chain by means of the ampermeter and the voltmeter. For this purpose connect the ampermeter in a chain consistently, and the voltmeter in parallel to the measured site, by its ends. In a case with to constants current it is necessary observe polarity: attach positive contact of the device to a positive pole of a source, negative to negative. Take readings of these devices, respectively, in amperes and volts. Then find resistance of the site of a chain, having divided value of tension on it into value of current.

3. To measure resistance of the conductor without use of electric devices learn material of which the conductor is made, and find its specific resistance in the corresponding table. Then, measure its length in meters. After that, if the conductor has round section, by means of a caliper or a micrometer, measure its diameter in millimeters and find cross-sectional area for what build diameter in the second degree, increase by 3.14 and divide into 4. If section has other form, all the same find its area, it is specified in some conductors initially. After that specific resistance is multiplied by length of the conductor, and is divided into the area of its cross section. It will also be its resistance.

4. To find resistance of all electrical circuit, learn the EMF (electromotive force) of a source of current, it is always specified on it in volts. Then, learn its internal resistance. After that measure current in a chain, having turned on in it the ampermeter consistently. Find resistance, having divided EMF value into the current measured by means of the ampermeter, and from the turned-out result take away value of internal resistance of a source of current.

Author: «MirrorInfo» Dream Team