# Experiment to determine the resistance of a wire

**Typical setup To Measure The Resistivity Of A Wire**

Note:that the Battery/Cell and rheostat (variable resistor) can be replaced by a variable Power supply

**Equipment**

- 1m of constantan wire of nominal diameters 0.27 and 0.56 mm,
- 1m of nichrome wire of nominal diameters 0.27 and 0.56 mm
- Constant Voltage supply (constant meaning that changes will not be significant during the experiment),
- Either two multimeters or one ammeter and one voltmeter

**Procedure**
When handling the wires avoid stretching them or deforming by kinking. this introduces local restrictions that will affect the results.

- Take one of the pieces of constantan wire and record its diameter in three places using the micrometer screw gauge. Calculate the average. Set up circuit as shown in the diagram. The Resistance
**R**is the resistance wire (constantan nichrorome) that you will be trying to calculate. - Set the power supply to 1V. This limits the current through the wire in order to reduce any heating effect which may change the resistivity.
- Record the readings on the ammeter and voltmeter for 8 different lengths.
- Complete a table a suitable table and calculate the resistance of the wire for each length.

**Analysis**

For each wire plot a graph of resistance (y-axis) against length.

The resistance of a wire is given by the equation: R = ρ x l/A

Where R is resistance, ρ (pronounced 'rho') is the resistivity of the wire, l is length and A is its cross-sectional area.

The gradient of each graph will give you the quantity ρ /A

Therefore if you multiply the gradient by the cross-sectional area, this will give you the resistivity of the wire. (you can use the measured diameter to calculate the wire’s cross-sectional area)

Use the above method of analysis to calculate the resistivities for each wire.

Where to buy Resistance Wire

**The current details we have are V B Rewinds**:
They are selling resistance and copper wire at very competitive prices, are pleasant to deal with, and can turn orders round very quickly. Postage and packing are also very reasonable -

Their details are as follows:

Vivien Hepworth - Proprietor

V B Rewinds Retreat Colmworth Road Little Staughton Bedford MK44 2BY

Tel/Fax: 01234 376719 Email: vivienhepworth@btinternet.com

See also: