PHYSICS · Multi-part · CBSE · Physics · Current Electricity · Current Electricity
Problem
In a laboratory investigation, a student wishes to determine the resistivity of an unfamiliar metallic wire. The wire has a uniform diameter of 0.80 mm and is connected to a stable 9.0 V DC power supply whose internal resistance is negligible. The student cuts the wire to several different lengths, connects each length in turn to the power supply, measures the steady current, and records the data shown below.
Length ℓ (m): 0.50 1.00 1.50 2.00
Measured current I (A): 8.18 4.09 2.73 2.05
(a) For each length, calculate the corresponding electrical resistance of the wire. Organize your results in a table.
(b) On appropriately labeled axes, sketch a graph of resistance versus length. Draw a best-fit straight line through the plotted points and determine its slope. Explain how the slope is related to intrinsic properties of the material and geometry of the wire.
(c) Using the slope from part (b) and the given diameter, compute the resistivity of the unknown metal. State an appropriate unit with your answer.
(d) Standard reference values for resistivity at room temperature are 1.68×10−8Ωm for copper, 4.90×10−7Ωm for constantan, and 1.10×10−6Ωm for nichrome. Based on your result in part (c), identify the most likely material of the wire and justify your choice.
(e) Describe one systematic source of error in this experiment that could cause the resistivity you calculated to differ from the accepted value. Explain qualitatively how the error would affect the measured slope.