Science Questions

Do surgical implants attract lightning?

Sun, 16th Jan 2011

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Question

Matt asked:

My friend had a huge operation to correct double scolliosis and i have spent considerable time helping her recover. The operation involved fusing a titanium rod to her spine, to replace but not remove an old surgical steel one. I have nicknamed her the lightning rod as she is petrified to go out in the lightning.

 

Two questions; firstly is she more likely to attract a lightning strike? Secondly, could the metals in some way have an effect on radio signals as at times she appears to effect radios and mobiles just by being in close proximity to them or is this just coincidence?

 

Many thanks

 

Matt from Milton Keynes

Answer

Dave -   The answer is yes, but only a very, very little bit.  Okay, lightning is very, very highly charged. This charge will attempt to flow down to the ground.  The problem is air is an insulator so itís got to flow through something.  The way you can get electricity to flow through air, so that the voltage gets big enough, is if the electric field gets big enough, you can rip electrons off the air, they can then fly through the air and bash other electrons off. You've got a big conducting path which electricity can flow down.  Itís a bit like a wire and the lightning bolt can go down through this path. The air gets very hot, and you get thunder and lightning.  The shorter this path has to be, the better the conductivity route up before the lightning has to start, the easier it is for lightning to form. Lightning tends to strike the lightning rod before it will strike something below the lightning rod because it is an easy path to get to Earth.  So you're friend would be an ever so slightly better route for the lightning to go than you are because sheís got this big metal rod down her back.  Actually, compared to air, you're a very, very good path, so itís going to be a trivial difference and if she actually had a big sharp, pointy thing coming out of the top of her head, that might have more of an effect but I very much doubt that she has.

Chris -   Because lightning conductors don't actually protect a building by attracting lightning.  They actually deflect the lightning around the building by effectively creating a sort of shield or coronal discharge of electrons flowing around the building and that provides a lower resistance route to ground for the lightning.

Dave -   Yeah, they do two things.  One of them is that they are a good path.  If lightning is going to hit the building, itíll hit the lightning rods, and therefore, the building will not catch fire, and the second one is that they can essentially discharge the lightning in that general area, they discharge and so itís less likely to strike in that area.  But the radio thing I think is quite likely because essentially, she does have a great big piece of metal in her back, a big piece of metal that acts like an aerial and can reflect radio waves, and do all sorts of strange things to it, in the same ways you can to a slightly lesser extent.  So yes, I'm sure she does affect that.

Chris -   Donít let her come around my house then because I have a terrible job picking up anything where I live.

Dave -   She might improve it.

Chris -   She may improve it even?  Oh well, okay then Iíll plug her in.

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Matt asked the Naked Scientists: My friend had a huge operation to correct double scoliosis and i have spent considerable time helping her recover. The operation involved fusing a titanium rod to her spine, to replace but not remove an old surgical steel one. I have nicknamed her the lightning rod as she is petrified to go out in the lightning. Two questions; firstly is she more likely to attract a lightning strike? Secondly, could the metals in some way have an effect on radio signals as at times she appears to effect radios and mobiles just by being in close proximity to them or is this just coincidence? Many thanks Matt from Milton Keynes What do you think? Matt, Tue, 23rd Nov 2010

Matt:

You are over thinking this situation. If you were to carry around a steel or copper rod wherever you went, but avoided walking in the middle of a golf course in a thunder storm, do you think you would be in any danger? Titanium is only weakly reactive to electromagnetic fields. Further, we all effect radio reception and I haven't had any problems from this. Standing in just the right place to improve reception has, on occasion, allowed me to listen to the news in a remote location.

Steve SteveFish, Mon, 29th Nov 2010

It's not just people on golf courses who get hit (though there are a lot of them)
More importantly, you are already a conductor. If the lightning is prepared to break down a mile or so of air to reach a conductor do you think it will know or care about a sightly reduced resistance of what it hits?
The point about golfers getting hit is that they are already the tallest thing around (because they are standing up on a flat field) and they then demonstrate a lack of understanding of physics by waving a stick above their heads.
Bored chemist, Mon, 29th Nov 2010

Resistance is futile!
Well, it's not the whole story anyway.
If the implant is made of a ferromagnetic or paramagnetic alloy then the increased inductance of the path of electric current past it might make the implant-free person an easier path to ground. Bored chemist, Wed, 19th Jan 2011



er, wouldn't the increased inductance increase the impedance of the path to ground?

(the impedance of an inductor is proportional to its inductance) Geezer, Wed, 19th Jan 2011

Yes, that was my point.
The metal rod would decrease the resistance, but it would increase the inductance so the overall impedance might go up. In that case the person without the implant would be more likely to get hit.

"(the impedance of an inductor is proportional to its inductance)" Unless it isn't.
The reactance is proportional to the inductance, and the impedance is the vector sum of the reactances and the resistance. Bored chemist, Wed, 19th Jan 2011

Ah! I didn't read your post correctly.



Only if it's not a superconducting inductor. Geezer, Wed, 19th Jan 2011

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