MB Resistivity

8/13/2019 MB Resistivity

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Course Name

Instructor Name

Student(s) Name

Resistivity

The resistance of a conductor depends on several factors. The physical

shape and the type of material are factors that affect resistance. Two

conductors with the same physical shape but made of two differentmaterials have different resistances. The resistivity of the material is

the physical quantity that determines the resistance of the object.

The resistance of a wire is directly proportional to the length andinversely proportional to the cross-sectional area. This is similar to the

water flow in a pipe. The longer the pipe, the more the resistance tothe flow rate. But the greater the cross-sectional area of the pipe, the

greater the flow rate. The constant of proportionality that relates the

resistance to the length and the cross sectional area is the resistivity.

Temperature is another factor that determines the resistance of the

material. But in this exercise, the factors that will be considered arethe shape and the resistivity of the material.

STUDENT OUTCOMES

Through this experiment, students will learn:

- the factors that determine the resistance of the wire- how to determine the resistivity of the material

- difference between resistance and resistivity

MATERIALS

Tablet ! !omputer "aptop #heostat

"ogger ro Board with wire spools

$ernier !urrent robe ower %upply

$ernier &ifferential $oltage robe 'ires


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PRELIMINARY QUESTIONS:

(. 'hat are the factors affecting the resistance of anelectrical conductor)

*. +f the length of a wire is doubled and the diameter is halved,

how is the resistance affected) xplain.. 'hy is resistivity a material property) 'hat are the units ofresistivity)

PROCEDURE:

(. !onnect the !urrent robe to !hannel ( and the &ifferential$oltage robe to !hannel * of the computer interface.

*. pen the file /*0 hms "aw1 in the Physics withComputers folder. 2 graph of potential vs. current will bedisplayed. The meter displays potential and current readings.

. !onnect together the two voltage leads 3red and blac45 of the$oltage robe. !lic4 , and then clic4 to 6ero both sensors.

This sets the 6ero for both probes with no current flowing and with no

voltage applied.

7. 'ith the power supply turned off, connect the circuit asshown in the figure below. Ta4e care that the positive lead fromthe power supply and the red terminal from the !urrent 8$oltage robe are connected properly. Note:2ttach the redconnectors electrically closer to the positive side of the power

supply.

a m m e t e r


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7. %et the rheostat at maximum resistance and have theinstructor chec4 the circuit.

0. Turn the control on the &! power supply to $ andthen turn on the power supply.

9. 2djust the rheostat until the current probe reads .02.

;. #ecord the current probe and voltage probe readingson the table. pen the switch as soon as the readings have beenrecorded.

sing the same wire, repeat steps 9 ? ; for a differentcurrent probe reading.

(. #eturn the rheostat to the maximum resistance and repeatprocedures for the other wire spools.

ANALYSIS:

(. >sing hm@s "aw, compute the resistance of each spool ofwire.

*. "oo4 up the corresponding diameter of your wire from agauge number table. !alculate the cross sectional area of each

wire.

. !ompare the resistance of the wires with their respectivecross sectional areas. +s there a proportional relationshipbetween the two quantities) +f so, state the relationship into amathematical equation. 3>se A as your constant ofproportionality.5

7. !ompare the resistance of the wires with their lengths. +sthere a proportional relationship between the two quantities) +fso, state the relationship into a mathematical equation. 3>se Aas your constant of proportionality.5

0. !ombine the two mathematical equations obtained innumbers and 7. 'rite down the equation that shows therelationship between the resistance, the cross sectional area andthe length. The proportionality constant is 4nown as theresistivity.

9. >sing the equation that you got in number 0, compute theresistivity of the wires for each trial and compute the average.


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;. !ompare the average resistivity for wires made of thesame material but different lengths. &oes the resistivity changewith length) xplain.


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MB Resistivity