Last week, an Ars Technica writer was struck by lightning. He says that the 911 operators were concerned about whether or not he was wearing shoes at the time, but he didn't think it would make much difference. Apparently, air has a thousand times more resistance than hard rubber. Does this mean that wearing shoes wouldn't do anything?

What about with electrical wiring? I've seen electricity spark through the air before, but I don't think I've seen it go through rubber, especially a greater volume of it. Is there something I'm missing here, or have I just never considered it?

  • $\begingroup$ The comparison is meaningless because you can stand on half an inch of rubber, unlike air. If the writer hadn't been wearing shoes, he would not have been walking on air. He would have been coupled to the ground in a better way with bare feet than with shoes. $\endgroup$ – Kaz Jun 1 '13 at 8:33
  • $\begingroup$ @Kaz you're right that not standing on rubber shoes doesn't mean you're standing on air. It does mean there will be that much more air over your head though. It just doesn't matter if you're standing on the ground or not though. A bolt passing through your body is going to do the same amount of damage whether your standing on the ground, on shoes, or floating in the air. $\endgroup$ – Brandon Enright Jun 2 '13 at 3:50

At sufficiently high voltages almost everything conducts due in part to quantum tunneling of electrons. An insulator has a breakdown voltage which is the field strength required before it will start conducting.

Related to the breakdown voltage is the dielectric strength which is the minimum voltage over distance ($\mathrm{V}/\mathrm{m}$) before a material will conduct.

The table at Wikipedia lists dielectric strength of air as $3.0 \times 10^6\: \mathrm{\frac{V}{m}}$ and rubber at least five times better at greater than $15 \times 10^6\: \mathrm{\frac{V}{m}}$.

When it comes to lightening though, I doubt it matters much. The bolt of lightening overcame dozens or even hundreds of meters of air to strike. A few cm of rubber isn't going to matter. If the rubber is a bad path it'll just take the air around the rubber shoe soles.

Regarding the resistance of rubber versus air, resistance stops having much of any meaning once the breakdown voltage is exceeded. The current will form a plasma out of the material and plasmas are great conductors.


protected by Qmechanic Nov 4 '15 at 20:08

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