How good are smartphones at detecting all magnetic fields?

>>8557558
if you re using a smartphone app for conducting science experiments ,well... it's like measuring lenght with bananas. get yourself a megnetometer.

>>8557571
magnetometer whatev

>>8557558
I assume by "AC fields" you mean alternating magnetic fields. The Alternating Current forms fields that can be measured just as well with a magnetometer (really depends on the frequency though).

If you want to detect an alternating field, you could just use a radio. Most consumer electronic devices are tuned to oscillate in the GigaHertz range, which can be picked up by nearby radio receivers.

It really depends on what exactly you're looking for.

>>8557588
I'm looking for a place to store magnetic media (VHS, etc.) safely. I know I'm probably being paranoid but just for peace of mind it would be nice to know that where I'm storing them doesn't have any fields that are reasonably higher than the average field strength within my house. I don't need exact readings, just relative ones. e.g., I already know not to store them in one spot because it's evidently too close to the stove on the opposite side of the wall as the meter reads much higher in that area.

I'm not sure what I mean by "AC fields" to be honest. I just want to be sure that the tesla meter / magnetometer on my phone is actually able to measure all types of magnetic fields that could affect magnetic media. And if not, if there's a magnetometer out there that's actually affordable but will do the trick without me having to spend hundreds.

>>8557604
Just put the tapes in a case with a thin layer of iron, if you're that worried. Materials with a high magnetic susceptibility tend to be very good at screening external fields when they enclose a volume of space. Essentially they force the total flux to pass through the walls instead of penetrating the barrier. Pure iron could do this exceptionally well (like cutting the field strength by a thousand times) while only a few milimeters thick.

>>8557621
Thanks but this isn't an option - I'm going to be hanging them on a wall for display.

Assuming the only reasonable source of magnetism would be coming from behind the tapes in the case (e.g., from a stove behind the wall) and a little from the sides - would putting EMI / faraday foil on the back of the case have any effect?

Also, I just experimented with a small electric fan, and placing the phone on the electrical cord does cause the smartphone reading to fluctuate very slightly - as soon as I turn off the fan it stops, then starts again when I start it back up. I'm pretty sure it's coming from the wire itself and not the fan, because I was several feet from the fan and it only happens when the wire is touching a specific part of the wire.

Would this then suggest that to some degree my phone is capable of detecting AC magnetic fields?

>>8557637
>it only happens when the wire is touching a specific part of the wire.
*specific part of the phone

Yes your phone has a magnetometer in it already and it can detect AC or alternating/fluctuating magnetic fields fairly accurately. Aluminum foil WILL NOT block magnetic fields at all, don't even try it.

If you're serious about protecting your tapes, use mu-metal: http://www.ebay.com/itm/like/171082057513

https://en.wikipedia.org/wiki/Mu-metal

to be really effective, you really want a full box made out of it and put your tapes in the box.

however a sheet of it on the wall where you plan to put your tapes is better than nothing.

using iron like >>8557621 said is NOT a good idea because while iron will redirect magnetic fields... it itself is a fairly strong magnet. Just put your phone near some iron, you'll see your meter deflect wildly.

If your tesla meter app doesn't have a graph. Get one that has a graph for all 3 axises of your magnetometer.

like this one: https://play.google.com/store/apps/details?id=com.chrystianvieyra.android.physicstoolboxmagnetometer&hl=en

to clarify, >>8557621 is speaking the truth.

Its just not too good of an idea, even with thin sheets because iron itself is a fairly strong magnet of sorts, and FYI, magnetic fields get A LOT stronger the closer you are to them, so putting your tapes right up next to a sheet of iron has a better chance at flipping magnetic domains in your tape vs just leaving your tape out on a desk for the earth's magnetic field to play with it.