you need
• - Tester;
• - ruler or measuring tape;
• - Calculator.
Guide
1
Measure the resistance of the wire .For this to its ends connect tester included in the operation ohmmeter.On the screen of the device will be the electrical resistance wires in ohms, or their multiples, depending on the settings of the device.The wire thus should be disconnected from the power source.
2
Calculate the resistance using a tester that operates in ammeter and voltmeter.If the wire is a portion of the circuit, connect it to the power supply.To the ends of the wires parallel attach tester included in the operation of the voltmeter.Measure the voltage drop across the wire in volts.
3
Switch tester mode and turn it on ammeter in series.Get the value of the current in
the circuit in amps.Using the ratio obtained from Ohm's law, get the electrical resistance of the conductor.To divide the value of the voltage U for a current I, R = U / I.
4
example.Measurements showed that the voltage drop on the conductor 24, the current in it is 1.2 A. Determine the resistance.Find the ratio of voltage to current R = 24 / 1.2 = 20 ohms.
5
find resistance wire , without connecting it to a power supply.Find out what material is made of wire.As a specialized table to find the resistivity of the material in ohm ∙ mm2 / m.
6
Calculate the cross section of the wire , unless it is indicated initially.To do this, clean it from isolation if it is isolated, and measure the diameter of the conductor in mm.Define the radius by dividing the diameter of the number 2. Define the wire cross section , multiplied by the square of the number of π≈3,14 core radius.
7
Using a ruler or tape measure, measure the length of the wire meters.Calculate the resistance of the wire , multiplying the resistivity ρ of the material on the conductor length l.Divide the result by its section S, R = ρ ∙ l / S.
8
example.Find the resistance of the copper wire diameter of 0.4 mm and length of 100 m. The resistivity of copper is equal to 0.0175 ohms ∙ mm2 / m.Radius wire is 0.4 / 2 = 0.2 mm.The cross-section S = 3,14 ∙ 0,2² = 0,1256 mm².Calculate the resistance formula R = 0.0175 ∙ 100 / 0,1256≈14 ohms.