Magnet in mercury...

Thread Starter

Externet

Joined Nov 29, 2005
1,935
Good day.
Having difficulty visualizing / predicting the behavior. Can I have your opinion please ?

Would a magnet moving or spinning submerged in mercury create electrical currents in the (conductor) mercury ?
 

crutschow

Joined Mar 14, 2008
30,803
Would a magnet moving or spinning submerged in mercury create electrical currents in the (conductor) mercury ?
As long as the magnet is moving relative to the mercury, then it should generate an eddy current.
Whether the metal is liquid or solid should make no difference.

Three cheers for the deciBel !
 

Alec_t

Joined Sep 17, 2013
13,153
The mercury surrounding the magnet forms a closed circuit, so the induced current will also create a magnetic field. The maths is above my payscale, but I bet Murphy's Law ensures the field created opposes the magnet's field :).
 

Thread Starter

Externet

Joined Nov 29, 2005
1,935
Thank you gentlemen.

1.- Do not understand the video. Is there a motor - where- doing what ? Spinning the mercury ?

2.- Did a test which am unsure is proper, with negative results.
Placed two probes in seawater as conductive liquid instead of mercury. Moved a powerful neodymium magnet in it. No effect registered on a 20mV/div

Is that a wrong way to 'design' the test ?

The video for the above is 22 MB; do not know how to shrink it to fit here. Am clumsy to link it; perhaps will work :
----> https://www.dropbox.com/s/k8pyawdbm9kp149/P1010946.MOV?dl=0
 

Ya’akov

Joined Jan 27, 2019
6,575
Thank you gentlemen.

1.- Do not understand the video. Is there a motor - where- doing what ? Spinning the mercury ?

2.- Did a test which am unsure is proper, with negative results.
Placed two probes in seawater as conductive liquid instead of mercury. Moved a powerful neodymium magnet in it. No effect registered on a 20mV/div

Is that a wrong way to 'design' the test ?

The video for the above is 22 MB; do not know how to shrink it to fit here. Am clumsy to link it; perhaps will work :
----> https://www.dropbox.com/s/k8pyawdbm9kp149/P1010946.MOV?dl=0
The mercury is forming the rotor of a DC motor. The description explains the setup.
 

ericgibbs

Joined Jan 29, 2010
16,393
Hi,
I assume most of us are aware of the toxic effects of Mercury fumes.?
E
https://www.who.int/news-room/fact-sheets/detail/mercury-and-health

Clip:

The inhalation of mercury vapour can produce harmful effects on the nervous, digestive and immune systems, lungs and kidneys, and may be fatal
. The inorganic salts of mercury are corrosive to the skin, eyes and gastrointestinal tract, and may induce kidney toxicity if ingested.31 Mar 2017
 

xox

Joined Sep 8, 2017
789
That mercury toxicity is where the term ,"mad as a hatter" comes from. Mercury was used to make top hats.

https://www.history.com/news/where-did-the-phrase-mad-as-a-hatter-come-from

Yes back then it was far worst. Our school for example was once evacuated and then closed down for several weeks after some precocious teenager either spilled or poured it on the floor of one of the classrooms. He was apparently rather ignorant of the dangers. Which is probably why it is a good idea to preamble such demonstrations with some sort of warning. Any competent instructor surely must follow a clear safety protocol. Anyway at university that is of course per school guidelines. Youtubers sometimes just present the material without much context.
 

Ya’akov

Joined Jan 27, 2019
6,575
Mercury is very toxic, if ingested. But liquid mercury alone is not at all dangerous The vapor pressure of mercury is about .002mmHg which means it's basically completely non-evaporating at room temperature and atmospheric pressure.

Introducing it into the body, though, is bad news.
 

ericgibbs

Joined Jan 29, 2010
16,393
Hi,
Please take care:

At room temperature, exposed elemental mercury can evaporate to become an invisible, odorless toxic vapor. If heated, it is a colorless, odorless gas. Learn about how people are most often exposed to elemental mercury and about the adverse health effects that exposures to elemental mercury can produce.21 Dec 2021
Basic Information about Mercury | US EPA

https://www.dw.com/en/just-how-dangerous-is-mercury-anyway/a-16522491

This liquid form of mercury is especially dangerous because it vaporizes at room temperature. And when it vaporizes, it fills the air with tiny, invisible mercury atoms that are both scentless and soluble in oils or fats
 
Last edited:

Ya’akov

Joined Jan 27, 2019
6,575
Hi,
Please take care:

At room temperature, exposed elemental mercury can evaporate to become an invisible, odorless toxic vapor. If heated, it is a colorless, odorless gas. Learn about how people are most often exposed to elemental mercury and about the adverse health effects that exposures to elemental mercury can produce.21 Dec 2021
Basic Information about Mercury | US EPA

https://www.dw.com/en/just-how-dangerous-is-mercury-anyway/a-16522491

This liquid form of mercury is especially dangerous because it vaporizes at room temperature. And when it vaporizes, it fills the air with tiny, invisible mercury atoms that are both scentless and soluble in oils or fats
I appreciate your caution Eric. It makes sense to be specially careful with something that can poison you irreversibly and incrementally. The safe handling of mercury does include handling it only when necessary. Safe handling procedures changed radically for mercury over the years but room temperature liquid mercury has physics that say otherwise than the warnings now repeated.

I have to emphasize nothing I said was intended to suggest handling mercury, and that's for a good reason—it is easy to unintentionally expose yourself to its danger even if cool, undisturbed, and untouched mercury is not a danger. ercury is a danger in a way similar to high voltage, it is safe when handled correctly but so dangerous it shouldn't;t be handled unless necessary.

So, in practice I agree with your caution. Thanks for posting that.
 

Ya’akov

Joined Jan 27, 2019
6,575
Re-reading I discovered I somehow completely forgot to mention my main point in my original post! No wonder you responded as you did, @ericgibbs.

It should have included:

The dangers of mercury are recently overstated (like the famous toxic spill cleanup required for a broken CFL bulb) bu they are nonetheless real. Alternatives exist.

Though Hg is the only pure metal that is liquid at room temperature, alloys of Ga (gallium), which in pure form melts at a bit above room temperature can be made to be liquid at 25°C and usefully solid at only a little cooler.

A eutectic allow of Ga and In (indium) of 79% Ga/21% In is liquid has a solid/liquid phase change at 15.7°C. This means in normal indoor settings it will be liquid and act substantially like mercury. But cooling it just a little below summer indoor temperatures will make it solid.

Most liquid metal experiments, including the electrodynamic ones can be much more safely done with this alloy. It has low toxicity compared to mercury and its vapor pressure is substantially lower so it isn’t a vapor problem even in hot places or if heated to a considerable temperature.

So, that‘s it in more detail than I had originally intended. I thought I‘d mentioned Ga/In alloys as an alternative but I didn’t so now I have.
 

shortbus

Joined Sep 30, 2009
9,643
Yes back then it was far worst. Our school for example was once evacuated and then closed down for several weeks after some precocious teenager either spilled or poured it on the floor of one of the classrooms
It was worse where I went to grade school. Our teacher (4th grade) had a bottle of mercury and we were all made to take a copper penny and rub it with mercury to turn it a silver color!
 

MrAl

Joined Jun 17, 2014
9,549
Hi,
I assume most of us are aware of the toxic effects of Mercury fumes.?
E
https://www.who.int/news-room/fact-sheets/detail/mercury-and-health

Clip:

The inhalation of mercury vapour can produce harmful effects on the nervous, digestive and immune systems, lungs and kidneys, and may be fatal
. The inorganic salts of mercury are corrosive to the skin, eyes and gastrointestinal tract, and may induce kidney toxicity if ingested.31 Mar 2017
Hi Eric,

I've also read that there is mercury in fish too. Supposedly, the smaller the fish the less accumulated mercury because they havent lived as long absorbing mercury. We eat the fish, we eat the mercury.
I guess our skin turns shiny metallic i guess that is where robots come from :)
 

MrAl

Joined Jun 17, 2014
9,549
It was worse where I went to grade school. Our teacher (4th grade) had a bottle of mercury and we were all made to take a copper penny and rub it with mercury to turn it a silver color!
I had a ton of mercury thermometers now i have none and it's hard to find one now.
 

MrAl

Joined Jun 17, 2014
9,549
A changing magnetic field induces a current in a conductive material like copper or aluminum and it does not matter if it is solid or liquid although the degree of current and resulting magnetic field may be slightly different if the metals are melted.

What this SHOULD mean is that if you drop a magnet in a pool of water 100 feet deep and drop a similar magnet in a pool of mercury 100 feet deep the one in water will sink faster and not just because of the lower viscosity, it will also slow in the mercury because of the opposing magnetic force due to the movement of the magnet. So even if the mercury could have the same viscosity as the water the magnet in it would still sink more slowly.
 
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