If you wrap an active electric cord around your body, do you become an electromagnet?
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asked Sep 12, 2016 at 18:03
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1$\begingroup$ Possible duplicate of Using A.C or D.C to create an electromagnet $\endgroup$– Nick GrealyCommented Sep 14, 2016 at 12:19
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2$\begingroup$ I don't think it's a duplicate question: the major effects in this question are the fact that a wall power cord has both supply and return conductors, and that the human body isn't ferromagnetic. $\endgroup$– rob ♦Commented Sep 17, 2016 at 15:50
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4 Answers
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No. The power cord on a vacuum cleaner has both supply and return conductors, which produce opposing magnetic fields. The region of nonzero magnetic field is limited to a few cable diameters away from the cable.
Also the magnetic field due to an alternating current changes direction at 50-60 Hz, depending on your local power supply frequency.
If you wanted to turn yourself into an electromagnet you'd need to separate the hot and neutral conductors in the power cord, and wrap one around you clockwise and the other counterclockwise. Then the fields due to the two currents would add. You could convert to direct current if the alternation of the field direction bothers you. However since biological tissue is not ferromagnetic, the physical effects on you are pretty tiny.
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2$\begingroup$ Biological tissue is not magnetic, but sometimes people have magnetic implants. $\endgroup$ Commented Sep 12, 2016 at 22:22
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25$\begingroup$ I'm pretty sure that any effect would be negligible, since MRI machines use extremely strong magnets and don't pull people's blood around inside of them or anything like that. $\endgroup$ Commented Sep 13, 2016 at 5:53
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14$\begingroup$ @Ideogram Hemoglobin is not ferromagnetic at all. It's sometimes paramagnetic (when not oxygenated) and completely transparent when oxygenated. ncbi.nlm.nih.gov/pmc/articles/PMC1076743/?page=3 Our bodies in total are slightly diamagnetic because of water content. Diamagnetic means that it's repelled by the magnetic field, not attracted. One can levitate a frog by "nothing" but a magnetic field strong enough. Quotes, because it took 16T to levitate a tiny frog, and the biggest common human-sized magnets (ones in MRI) reach 3T. $\endgroup$– Agent_LCommented Sep 13, 2016 at 8:16
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2$\begingroup$ @Agent_L 7T scanners are quite common nowadays though. $\endgroup$– FirebugCommented Sep 13, 2016 at 18:46
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15$\begingroup$ To anyone reading, do NOT try this experiment without serious expertise. There's risk of eletrocution if any of the wires you're invasivaly messing with gets damage to the insulation. $\endgroup$ Commented Sep 14, 2016 at 13:01
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Okay, accuse me of having too much time on my hands, but here's what I did:
If you can't tell from the pic. I wrapped the vacuum cord around a steel bar. I turned on the vacuum and tried to pick up the screw. Absolutely nothing not even a hint of attraction so maybe BowlofRed has a point.
In case the comment gets deleted later, here is BowlofRed's comment:
The power cord has two conductors in it. The current is moving in opposite directions in each, so the net current flow through the cord is zero. No net current, no bulk magnetic field. – BowlOfRed
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2$\begingroup$ You can get a measurable magnetic field from wrapping an appliance cord in a circle if the current in the cord is unbalanced. For example, this happens whilst someone (or the bathtub lol) is being electrocuted. (Hopefully you have a RCD safety switch so 300 ms or so later it trips and cuts the power). Another unlikely scenario is for the appliance to be hit by lightening at the same time you are playing hola hoops with its cord - that would also induce current going in the same direction in all of the conductors of the cord. $\endgroup$– iheggieCommented Sep 17, 2016 at 7:01
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$\begingroup$ You are using an AC voltage (and thus an AC current). How would you expect it to work without a DC current? $\endgroup$ Commented Sep 17, 2016 at 15:43
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[Note: this answer is about a variation on this question: what if your finger is wrapped in a single conductor coil carrying current in one direction, which produces a concentrated magnetic field? This eliminates the slight red herring of the net current being zero in two parallel conductors carrying opposite and equal currents to and from the same two-terminal device, which leads to cancellation of the magnetic fields, except at very close proximity to the conductors. The question of a body part being used as the core for a proper coil is independently interesting.]
In a frame of reference in which some electric charges are moving, we observe a magnetic field. A coil of wire concentrates this magnetic field. A coil can be wrapped around some core material which can further strengthen the magnetic field depending on the degree to which it possesses a property called permeability. Materials which do this are those which become magnetized, either temporarily while the applied magnetic field exists, or permanently.
Whether or not some appendage of your body acts in this way and to what extent depends on its permeability.
Permeability can be expressed in absolute terms or as relative permeability: the ratio to the permeability of free space. If something has relative permeability of 1, then it has the same permeability as free space. (And is definitely not a magnet, permanent or otherwise).
According to Table 1 in this paper entitled "Electromagnetic Field Modeling in Human Tissue", various human tissues are all listed as having a permeability of 1: i.e. approximately that of free space.
If an energized coil of wire is wrapped around your finger, there will be a magnetic field there passing through your finger making it look like it is an electromagnet, but your finger isn't actually doing anything; the field will be the same if your finger is removed.
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1$\begingroup$ An underrated answer IMO. Is missing the detail about the detail about there being no field anyway though because of currents in opposite directions. $\endgroup$– MyridiumCommented Sep 15, 2016 at 11:40
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$\begingroup$ So the conclusion is that you become an electromagnet, but no more so than air becomes an electromagnet when wrapped with the same wire. $\endgroup$ Commented Sep 19, 2016 at 11:58
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The answer is no, because the electric field of each wire cancels the field of the other wire. But even if you wrap yourself many times with one wire and connect the ends to electric power, you will not become a "measurable" electro-magnet. The reason for this is that the amount of ferromagnetic material in your body (blood iron, etc.), is very small.
