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Resistivity.My aim is to measure the resistivity of the wire alloy Constantan

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Physics course work,



Resistivity is a property of a material, so it only depends on the material not the size and shape.  Resistivity is usually a small number.

To find resisitivity you need to use the formula,

Resistivity (p) =resistance(   ) x cross-sectional area(m²)

                                  Length (m)

My aim is to measure the resistivity of the wire alloy “Constantan”

List of apparatus,

Power, (Direct current) range of 0V-12V

Voltmeter, range of 0V-10V,

Ammeter, range of 0A-10A,

Meter length of Constantan wire,

Meter rule,

6 connecting wires,

Crocodile clips,

Micrometer, range of 0-50mm,   0.005mm




The variables involved with the experiment will be the length of the wire,  as we decrease the length of the wire the resistance should decrease.  The constant which will be used is the current, I will use the same amount of current through out the experiment to derive different voltages.


  1. Connect one-meter length of 0.46mm diameter “constantan wire” to the meter rule using tape to secure it and make sure it stays in position.
  2. Connect the first crocodile clip at 0cm positioned on the ruler.
  3. The second crocodile clip is now connected at relevant positions along the meter rule depending on the required length.
...read more.





Design Justifications,

I chose to stay below 3Volts because when I tested how many volts needed to heat up the constantan wire it was just over 3Volts, so if I stay below 3Volts then there should be no problems with temperature change in the wire.

The experiment I carried out to find the temperature change was by wrapping a section of the constantan wire around the bottom of a thermometer.  I then sent a current through the wire and took note of when the temperature started to rise.

This was at 0.33A.

I found the radius of the wire by using a micrometer to read the diameter then divided the reading i got by two.

To find the length of the wire i used a meter rule, which was taped to the side of the wire.

I found the cross-sectional area of the wire by using the radius that i found and squaring it then multiplying it by pie.

Then using the area i found the length/area which was =L


Then to get the same amount of amps i set the ammeter to 0.25A at the beginning of every experiment.  

To get the volts i read the voltage of the voltmeter when the current was set.  

...read more.



My final result,

Is that there were two results i have derived for the resistivity of constantan alloy, which are,



Were both good values and were good because I had to put up with possible errors.


The reliability of the techniques i used was good for this experiment.  I believe the results would have been more accurate using more accurate and expensive equipment.  

The only way to make my experiment more reliable would be to do it again and again.  This will make it more accurate.


With taking the possible errors in to account,

If i were to improve this experiment i would probably do the experiment with different pieces of constantan wire to make sure that the wire i was using for the experiment was not faulty.

When doing the experiment in the future I would repeat the experiment over a lot more times to get a better average to use for each variable, and a lot more accurate results.

I would try to make sure I don’t get any anomalous results which would make my experiment just that little bit more accurate.

...read more.

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