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Resistance of a resistor is determined via geometry of the resistor
Typology: Lab Reports
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Qty Item Parts Number 1 Voltage Source 850 Interface 1 Resistance Apparatus EM‐ 8812 1 Sample Wire Set EM‐ 8813 1 Voltage Sensor UI‐ 5100 2 Patch Cords
The purpose of this activity is to examine how the resistance of a resistor is determined via geometry of the resistor, and the material which it is made of. Also, to further the student’s understanding of the difference between resistance and resistivity.
Ohm’s Law describes the relationship between the resistance R of a wire, the voltage drop across it, V, and the current through the wire, I. This is formally given by the equation:
The resistance of the wire is a function of both the geometry of the wire and the material that the wire is composed of. This is formally given by the equation:
Where here L is the length of the wire, A is the cross‐sectional area of the wire (in this simple equation we are assuming the cross‐sectional area is constant along the entire length of the wire), and ߩ is the resistivity of the material the wire is composed of. The SI units of resistivity are Ohms∙meters, Ω∙m, and it is a quantification of how difficult it is to move a current through a length of the material. This equation shows us that resistance is a property of the object, while resistivity is a property of the material the object is made of. Due to this distinction it is really incorrect to say things like, “Copper has a low resistance.”, because copper has a ‘low’ resistivity. If you take a copper wire and double its length, you double the resistance of that wire, but the value of the resistivity of the copper in that wire doesn’t change.
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Brass 0.050 inch Diameter Cross‐Sectional Area________________ L(cm) L/A(cm‐^1 ) V(V) I(A) V/I=R(Ω) R(μΩ)
Brass 0.032 inch Diameter Cross‐Sectional Area________________ L(cm) L/A(cm‐^1 ) V(V) I(A) V/I=R(Ω) R(μΩ)
Brass 0.020 inch Diameter Cross‐Sectional Area________________ L(cm) L/A(cm‐^1 ) V(V) I(A) V/I=R(Ω) R(μΩ)