Electrical Resistance of Water

GoldDigger

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In an appropriate semiconductor junction they can excite an electron (or hole) to move from on side of the junction to the other. This is what happens in a photovoltaic solar cell.
In ordinary insulating material, like glass or brick the electrons are promoted from a captive electron shell to a captive shell with higher energy. At some point the electrons will drop back down again, giving energy in the form of light or heat, just not immediately.
 

mbrooke

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In an appropriate semiconductor junction they can excite an electron (or hole) to move from on side of the junction to the other. This is what happens in a photovoltaic solar cell.
In ordinary insulating material, like glass or brick the electrons are promoted from a captive electron shell to a captive shell with higher energy. At some point the electrons will drop back down again, giving energy in the form of light or heat, just not immediately.


Is this why light hitting a surface turns to heat energy?
 

gadfly56

Senior Member
Location
New Jersey
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Professional Engineer, Fire & Life Safety
Is this why light hitting a surface turns to heat energy?
Pretty much. The incoming is mostly visible and UV, as water in the atmosphere blocks out most IR. Once a photon hits a surface and transfers that energy to an atom, that energy is transferred to another atom (conduction) or sent back out as lower frequency IR (radiation).
 

Sahib

Senior Member
Location
India
In addition, the photons hitting a surface exert pressure on it. In other words light is capable of work by itself revealing it is also made up of particles ie photons.
 

Sahib

Senior Member
Location
India
Electrons tightly bound, doesn't everything start conducting at some voltage? Even porcelain begins to look like copper?
Sure, an insulator starts to conduct or leak current at some voltage. But if that voltage is high enough to initiate considerable current, it would cause destruction of the insulator : thermal runaway.
 

GoldDigger

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Sure, an insulator starts to conduct or leak current at some voltage. But if that voltage is high enough to initiate considerable current, it would cause destruction of the insulator : thermal runaway.
In some practical cases electrons will move along the surface via resistance of surface contamination and ionization of air or other gas or liquid at gaps before the breakdown of the insulating material itself is reached.
Just a practical consideration to add to the theoretical. Breakdown in the bulk insulator, unless current is somehow limited, will generally result in destruction

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mbrooke

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In some practical cases electrons will move along the surface via resistance of surface contamination and ionization of air or other gas or liquid at gaps before the breakdown of the insulating material itself is reached.
Just a practical consideration to add to the theoretical. Breakdown in the bulk insulator, unless current is somehow limited, will generally result in destruction

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Is this why washing dirty insulators causes flash over?
 

Sahib

Senior Member
Location
India
Sure, an insulator starts to conduct or leak current at some voltage. But if that voltage is high enough to initiate considerable current, it would cause destruction of the insulator : thermal runaway.
Of course, a solid insulator would be destroyed due to excessive leakage current. But a liquid or gaseous insulator would not: only electrical breakdown happens.
 

Sahib

Senior Member
Location
India
A continuous stream of water on insulator carrying live line would cause flashover but not water spray.
 

GoldDigger

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NERC reports say otherwise. It has happened.
I don't see the water itself as a conductor causing flashover, but I could see it interacting with dry surface contaminants to create a conductive path interrupted only by gaps small enough to break down.

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mbrooke

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I don't see the water itself as a conductor causing flashover, but I could see it interacting with dry surface contaminants to create a conductive path interrupted only by gaps small enough to break down.

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Right, thats my point.
 

mbrooke

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I don't see the water itself as a conductor causing flashover, but I could see it interacting with dry surface contaminants to create a conductive path interrupted only by gaps small enough to break down.

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Before anyone says I meant otherwise see this:

 
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