I did not manage to figure this one out. Can you?

The usual answer relies on an assumption that may not be true.

I think the middle of the magnet doesn't have attractive power. So given A and B, we can do the following procedure...

 

You take one end of A and apply it to the middle of B. If there's attraction then A must be magnet. If there's no attraction, B must be the magnet.

 

Or you could break both A and B into two pieces each. If the pieces attract each other, the original rod is magnetic. If the pieces don't attract each other, the original piece is not magnetic.

 

 

The usual answer relies on an assumption that may not be true.

I think the middle of the magnet doesn't have attractive power.

That's the unreliable assumption.

Edited May 3, 201510 yr by John Cuthber

Hang a rope off the ceiling. Hang rod A on the rope so that it's balanced and not moving. Observe for a bit. If not starting to rotate change orientation by 90 degrees (if you had a pure luck of accidentally orienting it N-S the first time). Moving? Magnet. Not moving? Rod B is the magnet. Repeat the experiment with rod B to confirm that there is in fact a magnet in the room.

I did not manage to figure this one out. Can you?

The answer is that there are no metal objects but plenty of other things so you get a dish put one at a time into it and float it in a plastic bucket of water, and see which one aligns with the Earth's magnetic field.

Edited May 4, 201510 yr by Robittybob1

Hmm... this magnet piece might not be a straight bar magnet with two poles (N at one end, S at other end). Instead it might be a Halbach array or something... So, some of above mentioned tests might not work... Also, it is hard to break a metal road with no metal tools on hand... So I guess the best answer is the one that says you should take a large stone and hammer one of the pieces heavily and check if magnetic force decreases (or if you have a pile of coke & wood on hand, you can try to heat one piece above its Curie temperature). You have 50% chance that your test will be non-destructive, lol.

If you (and the bits of metal) are in the Earth's magnetic field then both of them will be magnetised (obviously, one more that the other) so the alignment with the North South line won't work.

 

That's the unreliable assumption.

 

How so? The magnet must have 2 poles. No matter how they're oriented you should be able to detect varying field strength??? (Unless the magnet was too weak, which would ruin the puzzle.)

In a real scenario, you could simply run them along a wall. Nails and screws are made of ferrous metals, and concrete contains steel rebar. One will stick to the wall, one will not.

How so? The magnet must have 2 poles. No matter how they're oriented you should be able to detect varying field strength??? (Unless the magnet was too weak, which would ruin the puzzle.)

Imagine I have a big magnet on the table and I hang a needle above it.

Th field of the big magnet will induce a field in the needle and so the needle will end up aligned with the magnet.

It still works if the big magnet is the Earth.

I would try stroking from the middle to one end along the length of one of the rods with one end of the other held perpendicular, many times. Then touch each end of the stroking rod to the target end of the stroked rod. If there is a notable difference in the draw, the stroking stick is probably the magnet. If no or negligible difference, the stroked stick probably was.

 

I'm not betting large sums on that being clear and definitive, though.