Specific resistance (ρ) is one of sizes which characterizes the electrical resistance of the conductor. If material of the conductor is known, then it is possible to find this size from the table. If the conductor is made of unknown material, specific resistance can be found differently.
It is required to you
- - table of specific resistance;
- - tester.
Instruction
1. Define material of which the conductor is made. After that find value for this material in the table of specific resistance. Pay attention that in it two values, as a rule, move. One in Omm - it undertakes in case in calculations section of the conductorof it is measured in m². If the section of the conductor is measured in mm², then in this case it is better to take value in Ommm²/м.
2. In case material of the conductor is unknown, find its specific resistance independently. For this purpose, by means of the tester switched to the ohmmeter mode find the electrical resistance of the conductor in Ohms. Then, measure by a roulette or a ruler its length in meters, and a caliper diameter in millimeters. To calculate the specific resistance of the conductor number 0.25 increase by its electrical resistance, number π ≈ 3.14 and diameter of the conductor in a square. The received number divide into length of the conductor ρ=0.25∙R ∙π ∙ d²/l. Where R is the electrical resistance of the conductor, d is its diameter, l is length of the conductor.
3. If for any reasons to find resistance of the conductor directly it is not possible, determine this size, using the law of Ohm. Connect the conductor to a current source. Connect to it the tester tuned into measurement of current, consistently and measure the current proceeding on the conductor in amperes. Then, switch a tester to voltage measurement and attach it to the conductor in parallel. Receive value of voltage drop on the conductor in volts. If the conductor is connected to a DC power source, at connection of a tester consider polarity. Find resistance of the conductor, having divided value of tension into R=U/I current. After that calculate specific resistance on above to the stated technique.