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Author Topic: Which Electromagnetic Wave Builds Electric Charge (in Metal) the Fastest?  (Read 481 times)

Offline Simple Simon

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Forks in microwave ovens are known to spark. However, as far as I've heard, laser in the infrared and visible light spectrum don't build much or any charge on metal. I was curious about which electromagnetic wave builds charge the fastest/most efficiently. I expect one of the ionizing types of radiation?

PS: I assume that this only happens with metal, but for all I know some EMW might build a charge in other things.

Thank you for your help.
« Last Edit: 20/07/2016 09:21:13 by Simple Simon »


 

Offline evan_au

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Quote from: Simple Simon
Forks in microwave ovens are known to spark.
The breakdown voltage of dry air is about 1 million volts per meter.
Voltage differences as low as 100-200V can produce visible sparks, if the objects are almost touching.

The following website suggests that a domestic microwave over (850W) can generate electric fields inside the oven of 2000V per meter. So its not surprising that close conductors in a microwave oven can cause sparks.
http://www.astrosurf.com/luxorion/qsl-em-radiation2.htm

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which electromagnetic wave builds charge the fastest/most efficiently?
I suggest any wave at over 1000V peak will produce visible sparks.
The frequency most available in homes and labs is 50Hz or 60Hz (depending on the country).
A step-up transformer will produce dramatic sparks.
Note: Do not try this at home!

Van De Graaf generators (DC) or Tesla Coils (kHz) also produce dramatic sparks, and are available in laboratories and science museums.

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laser in the infrared and visible light spectrum don't build much or any charge on metal
I assume here that you are trying to emulate the photoelectric effect? (Einstein got his 1915 Nobel prize for explaining this.)

It requires several eV of energy to eject an electron from metal, so this works best with violet, ultraviolet and higher frequencies (not infra-red: not enough energy).

As soon as you eject an electron, the metal becomes charged, and then it takes even more energy to eject another electron.
So measuring the photoelectric effect is usually done in a vacuum (which also avoids buildup of insulating oxides on the surface). A circuit is used to return the emitted electrons to the metal, so a charge does not build up and halt the electron emission.

See: https://en.wikipedia.org/wiki/Photoelectric_effect
 
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Offline Simple Simon

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Hmm, interesting. Thank you, Evan!

Do you know the math formula for calculating the buildup of charge with the photoelectric effect, or what I can look for to find it? I'm interested in how much you can build up with UV lasers or the like. I tried to look for the formula, but couldn't seem to find it.
 

Offline PmbPhy

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Forks in microwave ovens are known to spark. However, as far as I've heard, laser in the infrared and visible light spectrum don't build much or any charge on metal. I was curious about which electromagnetic wave builds charge the fastest/most efficiently. I expect one of the ionizing types of radiation?

PS: I assume that this only happens with metal, but for all I know some EMW might build a charge in other things.

Thank you for your help.
Electromagnetic waves don't exactly cause charge to build. It causes a difference in potential between two conductors. When the air breaks down due to high voltage it causes charge, in the form of electrons, to flow from one conductor to the other in a direction opposite the electric field.
 

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