How Change in Distance From A Current-Carrying Wire Affects Magnetic Field Strength

Background | The Problem | Variables | Hypothesis | Procedure | Raw Data | Graphs | Conclusion | Links | Bibliography | Return to Research

 

Background .:.Top

Since I was a young child, I’ve always been fascinated by engineering and problem solving. I loved finding solutions to problems that arose in my community because it allowed me to use the skills I learned in class and apply them to the real world. Earlier this year, when my physics teacher introduced my class to our unit on magnetism, I immediately became sucked into the world of magnets and how they’re used in our society, mostly in plain view, without us knowing. As someone who is interested in joining the military after college, my research mostly involved the use of magnets in combat settings by soldiers or machinery that assists them.

The study of magnetism, although it was discovered around 600 B.C., is a relatively new topic in terms of understanding and application to our lives. Dating back to ancient Greece, legend says that magnetism was first discovered by a shepherd named Megnes. They say one day Megnes was herding his sheep through the mountains. Suddenly, he noticed the ferrule of his stick and the nails in his sandals got stuck to a rock. The iron in his stick and sandals had become attracted to the magnetic rock. The stone was later named magnetite, after the name of the shepherd who stumbled upon it.

Another pre-twentieth-century tale of magnetism being used is when a Chinese emperor used magnets to save his palace by constructing gates made of lodestone, a variety of magnetite. The enemy's metal armor would get attracted to the magnetic gates, thus thwarting them from going any further. This is one of the first instances of magnets being used in a combat setting, but it definitely is not the last.

Prior to the year 1820 A.D, scientists believed electricity and magnetism to be unrelated. Along came a scientist named Hans Christian Oersted. Oersted, who was presenting a demonstration to some science students, was trying to show them that electricity and magnetism are not related. He placed a wire with electric current flowing through it next to a compass, which has a magnetic needle. As he expected, the needle of the compass didn’t move. It just kept pointing toward Earth’s north magnetic pole. Following the demonstration, a curious student held the wire near the compass again, but in a different direction. To the surprise of Oersted, the compass’ needle swung toward the wire so it was no longer pointing north. This discovery intrigued Oersted, so he turned off the current in the wire to see what would happen to the compass needle. The needle swung back to its original position, north. Oersted made the discovery that an electric current creates a magnetic field.

Oersted’s discovery has allowed modern day scientists to discover there are many more uses for magnets than a compass, whether it be in the military or civilian world. One of these uses would be mine sweepers, which employ magnets to determine the location of mines in combat zones. Furthermore, the military, along with the public, use magnets to remove foreign objects, such as nails or spare parts, from the runways of airports. Just one of these objects can ruin hundreds of peoples' day. All of these instances, along with many others, made me wonder-- How do people know how far to make their magnets away from their target in order to be effective?

 

The Problem .:.Top

The purpose of this investigation, therefore, is to determine the relationship between the magnetic field intensity of a coil of wires and the distance between my measuring tool and the wires.

 

Variables .:.Top

The independent variable in this experiment is the distance from the wires which I measured the magnetic field intensity. The dependent variable is the magnetic field intensity, measured in mT. As for control variables: the current coming from the power supply, and the resistance of the wires which carried the current-- the wires were not changed throughout the experiment as to not change the resistance by introducing new, fresh wires.

 

Hypothesis .:.Top

I believe that the variables will have an inverse relationship; that is, as the distance from the wires increases, the magnetic field intensity will decrease.

 

Procedure .:.Top

To collect my data for this experiment, I used a bundle of wires with thirty windings and connected it to a power supply with a constant power of 4.77 amps per wire. 4.77 amps in each wire would result in a total power of 143.1 amps, or 4.77 x 30. I then got a ruler and placed it where I estimated the center of the wires would be on the table. The ruler was used to measure how far I would move my magnetic field sensor every trial. I decided on increments of 0.002 meters, or 2 millimeters. This would allow me to collect a good number of data given that I would be taking 35 different variations. For each variation, I would measure the distance from the wires, then press the spacebar on my computer to begin measuring the magnetic field 100 times in five seconds. I used the computer program Logger Pro to gather my data.

 

The only possible ethical or safety concern I can think of that would arise from conducting this experiment would be getting shocked by the wires, but I don’t think the current was high enough to do any damage.

I manipulated my independent variable by changing the distance of my magnetic field sensor for each variation by 2 millimeters. I measured my dependent variable by using Logger Pro to collect the data from a Vernier Magnetic Field Sensor. My control variables remained constant because my power supply never changed in how much current it was sending into the wires, and my wires were never changed so the resistance stayed constant.

 

Figure 1 : Diagram of my lab setup

Raw Data .:.Top

 

Figure 2: Raw Data

Data: Excel .:. Text

 

Graphing my Data .:.Top

Chart

Figure 3: Graph of Raw Data

I first graphed my raw data in Graph 1. This resulted in an exponential graph, so I decided to linearize my data in order to process the relationship between distance and magnetic field strength easier. This is shown in Figure 3.

Figure 4: Linearized Graph

My linearized graph had an R value of 1, which means the data has perfect positive correlation. This shows that the relationship between distance and magnetic field strength is correct in my experiment.

 

Conclusion .:.Top

In conclusion, the distance and magnetic field strength have an inverse relationship. My hypothesis, therefore, is correct. In my experiment I think there are a few errors, most of which could be fixed if I did the work over again. To start, I should have measured the magnetic field of the    room -- that is, take a trial with no current in order to zero out the sensor. Second, I think it would have benefitted me to take more time gathering my data to ensure I’m moving it precisely 2 mm every increment, or to make sure that the sensor is back to zero before starting another trial. Third, the current stayed at an almost constant number throughout the experiment, although it did jump up and down a couple of times. This fluctuation did not cause the data to lose credibility in my eyes because the change was so miniscule, and the uncertainty of the  device I used to measure the current is small enough to be negligible.

 Overall though, I believe my data is still valid, especially since the shape of my data’s graph matches up with the generally accepted belief for all scientists. I would like to see someone do an experiment about this subject but make it very much more precise and maybe apply it to different types of wires, or maybe make the distances moved each trial much smaller than my limited experiment was able to do.

 

Links .:.Top

https://byjus.com/physics/discovery-magnets/ - This website helped me to learn about the history of discovering magnetism from a folk tale.

https://flexbooks.ck12.org/cbook/ck-12-middle-school-physical-science-flexbook-2.0/section/22.2/primary/lesson/discovery-of-electromagnetism-ms-ps/ - This website also helped me to learn about the history of discovering magnetism, but from a scientific standpoint.

https://www.apexmagnets.com/news-how-tos/magnets-military-sky-ground/ - This website helped me to discover different applications for magnets in the military, something that interests me.

https://mpimagnet.com/education-center/magnetism-history-of-the-magnet - This website shows the types of magnets currently in use today, along with advantages/disadvantages and other information.

https://www.magcraft.com/history-of-magnetism-and-electricity - This website has a timeline of the history of magnets and helps to put into perspective just how long ago humans have been using some of the most useful and common items we have in our society today. It also shows that it doesn’t take a genius to discover something new, just someone who has the curiosity to find it and doesn’t stop when it gets hard.

 

 

Bibliography .:.Top

Admin. “Discovery of Magnets: History of Magnets: Uses and Its Types.” BYJUS, BYJU'S, 2 May 2022, https://byjus.com/physics/discovery-magnets/.

 

Admin. “Magnets in the Military: From the Sky to the Ground.” Apex Magnets Blog, 2018, https://www.apexmagnets.com/news-how-tos/magnets-military-sky-ground/#:~:text=Rare%20earth%20magnets%20are%20used,detection%20and%20detonation%20of%20mines.

 

Foundation, CK-12. “12 Foundation.” CK, 2019, https://flexbooks.ck12.org/cbook/ck-12-middle-school-physical-science-flexbook-2.0/section/22.2/primary/lesson/discovery-of-electromagnetism-ms-ps/.