## UnkleRhaukus 2 years ago how dangerous are magnetic fields ?

1. masterxnonos

they are always around us. in the environment they are harmless but if u go 140 T + it MAY affect u. but that only got generated once when they joined so many capacitors together to produce this pulse current that produced this huge magnetic field and it wasnt tested on human so no1 is really sure about it

2. UnkleRhaukus

i have recently got bought some small spherical neodymium magnets , how can i tell the frequency ?

3. UnkleRhaukus

or the magnetic field strength?

4. ghazi

well, felix it depends , how destructive can you make it :)

5. Kainui

Frequency? I didn't think magnets had frequencies. As for determining their strength, I suppose if you had a very sensitive ammeter you could connect it to a wire without anything in it and make a loop and then move the magnets in and out of the loop since a changing magnetic field induces a current. Once you measure the current you can use that to measure your magnetic field.

6. UnkleRhaukus

i didn't think magnets had frequencies either , but the second link seams to be going on about them, i do have an ammeter , what are the relevant equations for determining Tesla from amps ?

7. agent0smith

The frequency you're referring to in the second article is the frequency of the AC electricity, it's the frequency of how fast the magnetic field is changing, because the electric current is constantly changing direction. It sounds like higher frequencies are more dangerous because they create rapidly changing magnetic fields, which in turn induce currents within the cells of the human body. Static magnetic fields can't induce a current. A magnet like a neodymium magnet has a static magnetic field, it will only change if you move relative to the magnet... so avoid moving the magnet back and forth towards you over 100,000 times a second, and you should be fine :D

8. agent0smith

Static fields of small magnets are probably nothing to worry about health-wise. http://hobbieroth.blogspot.com/2009/10/are-static-magnetic-fields-dangerous.html @kainui @UnkleRhaukus the induced current will be proportional to how fast the magnetic field changes, ie how fast you can move the magnet, this likely won't allow you to learn much about a static field's strength. If you hold the magnet still, no current is induced. The faster you move it, the higher the current.

9. Kainui

I found something you might like to try! http://m.everythingscience.co.za/grade-11/18-electromagnetism/18-electromagnetism-03.cnxmlplus |dw:1355903564204:dw| They give you this equation. E is the voltage, N is the number of turns of wire, B is the magnetic field strength, A is the area of circular wire loop, theta is the angle at which you move the magnet towards the loop, and t is the time you do it in. $E=-N \frac{ \Delta(BAcos \theta) }{ \Delta t }$ With a little bit of magic I think we can combine this with ohm's law and also look online and measure the resistance by knowing the wire's material, length and diameter. http://www.cirris.com/testing/resistance/wire.html $\frac{ -IRt }{ NA }=B$ so by measuring I, the current and knowing the resistance R you might be able to measure it by timing yourself doing this. Although probably not since I have no idea what you'd be timing. I hope someone comes up with a way for him to measure his magnetic field strength lol.

10. Kainui

Actually this is overcomplicating it with this nonsense experiment and oversimplifying what a magnetic field "is". You could just compare the strength of a magnet that is in equilibrium with the force of gravity.

11. agent0smith

^yeah that would work, if you can time it. Another way to get some kind of measure would be to drop the neodymiummagnet through the centre of the loop of wire, while watching the ammeter for what current it peaks at. Then, use a less powerful magnet, drop it from the same height, through the centre of the loop of wire, and watch for the peak current on the ammeter. This will happen pretty damn fast though, the ammeter may not even react in time (or the human won't). This won't let you accurately measure the strength of the magnet, but it will let you compare your neodymium magnet to a weaker magnet, by comparing the difference in current induced.

12. agent0smith

^ my method is not very practical though, I'm not sure I'd recommend it :P

13. Kainui

I think you might also want to do more turns since that will increase your sensitivity. Also, I suggest not dropping it, but putting your magnets in a bag that you can then tie to a string and use a doorknob or something as a kind of pulley so that you can move the magnet back and forth easier

14. agent0smith

^ if you can keep the speed somewhat constant, that'd work. And yes, the more turns, the greater the induced current. The induced current is proportional to the number of loops of wire. If you have a solenoid, use that. Note that if the magnet is powerful enough and you drop it through something like a solenoid, the induced electric current may create a magnetic field strong enough to oppose the field from your magnet, and will briefly allow your magnet to float! Once it stops moving, the induced current stops, and it falls again.

15. agent0smith
16. agent0smith

Well it won't actually stop it completely, since as the magnet's fall slows down, the induced current is reduced, which in turn induces the magnetic field created by the current.

17. UnkleRhaukus

thanks for your response and lovely diagram what you said about frequencies makes sense, i think i should be safe from generating an alternating current. im not sure where i put my multimeter (with ammeter function) but when i find it ill try that set up with the solenoid, i have some precision scales but im not sure if is wise to expose them to the magnetic field , im gonna use a balance beam to find an equivalent weight of something else that i can weigh on my scale