Magnetic field ?

1. Jun 15, 2010

cragar

can we cancel a magnetic field with another magnetic field and get the field strength close to zero teslas , or maybe use a faraday cage .

2. Jun 15, 2010

K^2

You can't cancel a magnetic field. Divergence of magnetic field is zero. That means, a field line cannot be interrupted. You can only divert the field lines. You may think of that as pushing the field out. There are good ways to do that, however. Look up Meissner Effect.

3. Jun 15, 2010

cragar

thanks for your answer what about magnetic shielding , is it possible to construct something like a box and you could put something in it made of metal and a metal detector would not pick it up .

4. Jun 15, 2010

K^2

I'm afraid, any box like that you'll come up with will trip metal detector, which I imagine defeats your purpose.

5. Jun 15, 2010

cragar

what about using the meissner effect to get around it , will carbon set off a metal detector .

6. Jun 15, 2010

king vitamin

You can shield an object from a magnetic field by placing it in a spherical shell of high magnetic permeability, where the efficiency of the shielding increases with the permeability of the shell - see Jackson's Electrodynamics pages 201-203. I'm not sure if you could find a shell that wouldn't trip a metal detector, though...

7. Jun 15, 2010

stevenb

You can definitely cancel magnetic fields. This is particularly easy in linear, non-magnetic media. The best example I can think of is a very long coaxial cable. The equal magnitudes and opposite signs of the currents in the inner and outer conductors result in field cancelation outside the outer shield (at least for slowly varying fields).

Why are you talking about defeating metal detectors? Are you up to no good, or is this a scientific and harmless application? Either way, tricking metal detectors is more difficult than canceling magnetic fields.

8. Jun 15, 2010

Antiphon

If you wrap your gun with tinfoil and place it next to a pickle and cheeseburger the metal detector will think it's part of your lunch.

9. Jun 16, 2010

cragar

why , if we could cancel the field that is created from the metal it wouldn't appose the one created by the detector , not that it is east to cancel the field , what else would be tricky . This is purely scientific thread , i was just wondering if it could be done .

10. Jun 16, 2010

K^2

Metal detector doesn't measure magnetic field. It usually measures change of coil's inductance. In gate-type detectors, the gate is the coil. Any significant change to magnetic field geometry within the gate could trigger it.

11. Jun 16, 2010

cragar

ok but what ever it measure is , the change is caused by the B field ,