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Q & A: Water vs. Ice as Conductors

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Most recent answer: 11/01/2014
Q:
Why doesn't ice conduct electricity as well as water?
- Adam (age 15)
Imperial MO
A:
Hi Adam,

That's a great question. Since they are made of the same substance it makes one curious. The explanation is pretty basic. Electrical conduction requires the flow of charged particles. In water, these charge carriers are ions, some from dissolved salt and a few from water molecules that fall apart. When the water freezes those particles are either shoved out of the ice crystal or almost locked into place, much less able to move freely.

Hope that answers your question,

-Zach +mw

p.s. In ice the ions (mainly H+, the ion that moves most easily ) move round in a very interesting way. They rarely get enough energy to hop from one place to another. They actually tunnel quantum mechanically, a process which can't be pictured classically. Mike W.

(published on 01/24/2011)

Follow-Up #1: ice conducts electricity

Q:
is ice conducting electricity ?
- M.Niranjan (age 16)
Namakkal,TamilNadu,India
A:

Yes, but it's a poor conductor. The H+ ions don't tunnel around very quickly.

Mike W.


(published on 05/23/2013)

Follow-Up #2: Does quantum tunneling exist?

Q:
How do we know it quantum tunnels? We haven't directly observed quantum tunneling. And quantum is just a theory.
- Nathan (age 13)
Prior Lake MN U.S.A.
A:

I'm not sure why you say that "We haven't directly observed quantum tunneling." I've observed it in several systems. You see little things (electrons, atoms,...) moving back and forth randomly between different positions. At high temperatures, the rates depend on temperature because the little things need to pick up energy to get over some barriers. At low temperature, the rates don't depend on temperature because things just tunnel through the barriers. Just about everybody who does any sort of experiments at low temperature sees these sorts of things. Nuclear physicists also routinely see tunneling because many nuclear reactions have barriers too big to cross by ordinary thermal paths. In many cases the tunneling rates can be calculated from knowledge of the basic ingredients.  The observations are neither more nor less direct than those of anything else.

You also say "quantum is just a theory." What isn't "just a theory"? Gravity? Electromagnetism? The city bus schedule? All are just theories, more or less reliable. Quantum is one of the more reliable ones. Quantum theory (combined with special relativity, another mere theory) predicts the "gyromagnetic ratio" of an electron to about one part in 1011, which is a lot more accurate than the bus schedule.

Mike W.

posted without vetting until Lee returns from the Serengeti 


(published on 11/01/2014)

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