RP5-Resistivity of a wire

• Equipment: Constantan wire, voltmeter, ammeter, power supply, micrometer, ruler, crocodile clips.
• Set up: Measure the diameter of the wire at various points and calculate the mean. Connect the power supply to the constantan wire with crocodile clips and connect a ammeter in series and a voltmeter in parallel.
• Method: Measure the length of wire between the crocodile clips and record the voltage and current. Change the length and repeat. Then repeat the whole experiment twice more and calculate a mean resistance for each length.
• Graph: Plot a graph of resistance against length. The gradient will be resistivity divided by area.
• Analysis: Calculate cross sectional area of the wire using A = (pi d^2)/4. Resistivity is R A/L.
• Safety: Wire can heat up - disconnect crocodile clips in between measurements, do not touch wire; A tight wire can snap - wear goggles.