# Measurement of the resistivity of the material of a wire

The resistivity (ρ) of a material is one of the factors that determines the resistance of that material to the flow of electric current through it. In this experiment you measure the resistance (R) of a length of nichrome wire (length l) using an ohmmeter. You then measure the diameter (d ) of the wire using a micrometer screw guage. The resistance is given by the formula: R = ρ.l / A, where A is the cross-sectional area of the wire (A = πr²). The resistivity can be calculated from the formula: ρ = R.A / l.

Procedure:
1. Drag the slider to move the contact along the wire. At some point, record the resistance and the length of the wire.

2. Press "Get Micrometer". In this simulation a full turn of the circular scale reads from 0 to 50 and represents 0.5 mm. Note: initial reading = 3.72 mm, distance scaled up a little to make it more readable.

3. Press "Check Zero Error". A reading between 0.00 and 0.03 will show and therefore will have to be subtracted from later readings.

4. Press "Measure Diameter". Record the value and repeat until you have at least six readings. Calculate the average diameter.

5. Calculate the resistivity of the material of the wire.

6. Move the slider and therefore the sliding contact to a new position on the wire and again record length and resistance and again calculate resistivity.

Precautions:

• Ensure that the wire is straight when measuring its length. Measure only between the ohmmeter contacts.
• Take great care with the micrometer screw guage and the zero error, if present. Take the average of at least six readings as a very small error in the diameter of the wire causes a large error in the resistivity calculated.
• To avoid errors in the resistance readings press the ohmmeter contacts together and zero the ohmmeter, or else subtract the resistance of contacts and connections from later readings.

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