# The Naked Scientists Forum

#### paul.fr

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« on: 12/08/2007 11:13:24 »
The good Doctor has reminded my of an email i received, the challenge in the email is to find the magnet, and goes like this.

You have two straightened paper clips, one of them is magnetized, the other is not. Without breaking or manipulating one of the paperclips, or using any other material or tool. How can you tell which one is the magnet?

#### lightarrow

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« Reply #1 on: 12/08/2007 11:51:19 »
The good Doctor has reminded my of an email i received, the challenge in the email is to find the magnet, and goes like this.

You have two straightened paper clips, one of them is magnetized, the other is not. Without breaking or manipulating one of the paperclips, or using any other material or tool. How can you tell which one is the magnet?
Don't know if it works: I could take one of thos metal segments and approach with one of its points the exact centre of the other metal segment. If there is a force, then the segment I have in my hand is the magnet. If the magnet were the other segment, there wouldn't be any force, because the 2 forces produced by the two ends of the magnet would cancel each other. Probably it wouldn't be very easy to perform this experiment, however. Maybe there is a better way to solve the mistery.

#### eric l

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« Reply #2 on: 12/08/2007 14:10:59 »
Well, I can give you a way, but I am not sure whether it is consistent with "without... using any other material or tool".
I would take two circles of paper, one of the paperclips on each one, and then put each in turn on the surface of a tub of water.  The magnetized paperclip will turn around (with the circle of paper of course) till it is in north-south direction.
In fact, I would try to make a primitive compas with each and see which one works.

#### neilep

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« Reply #3 on: 12/08/2007 14:21:32 »
The good Doctor has reminded my of an email i received, the challenge in the email is to find the magnet, and goes like this.

You have two straightened paper clips, one of them is magnetized, the other is not. Without breaking or manipulating one of the paperclips, or using any other material or tool. How can you tell which one is the magnet?

Is it the one with a 'N' at one end and an 'S' at the other ?

To be honest...are ewe saying that all we can use is observation ?...and nothing else ?!!

#### Bored chemist

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« Reply #4 on: 12/08/2007 14:38:18 »
Eric, how do you know which way is North?
I think Lightarrow's solution is the best but both solutions neglect the idea that you can magnetise a straightened paperclip so that it has a South pole at each end and a North pole in the middle.

#### paul.fr

• Guest
« Reply #5 on: 12/08/2007 14:38:52 »
This is what the email says:

Put both of the straightened paper clips together. Mix them until you are not
sure which is which. The challenge is to figure out which one is the magnet
and which is not, but you cannot use ANYTHING else to test with. No fair
using the third paper clip, iron filings, a compass, or anything else. You are
also not allowed to break the paper clips. The two straightened clips are
all you need to figure it out.

oooh, Essien has just scored.

#### paul.fr

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« Reply #6 on: 12/08/2007 14:40:36 »
Eric, how do you know which way is North?
I think Lightarrow's solution is the best but both solutions neglect the idea that you can magnetise a straightened paperclip so that it has a South pole at each end and a North pole in the middle.

good thinking, BC

#### neilep

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« Reply #7 on: 12/08/2007 14:41:28 »
Would the magnetism in one of them give it a proclivity to locate itself in a different place than the non magnetised one (clawing at straws mode)

#### eric l

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« Reply #8 on: 12/08/2007 14:50:54 »
I should check if it works, but what I imagine is this :
- take up one of the straightened clips, letting the other flat on the table
- approach the middle of the clip on the table with one of the points of the clip I have in my hand
- if the clip on the table jumps up when I approach close enough, the clip in my hand is the magnetized one
- if it does not, approach a tip of the clip on the table with a tip of the clip in my hand, if the clip on the table jumps up now, the one on the table is magnetized
- if it still does not jump up, something has gone wrong
- if the table is to be considered an extra tool, just do the same thing on the floor.

#### Bored chemist

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« Reply #9 on: 12/08/2007 15:14:06 »
It's not easy in practice but I can still think of a way that wouldn't work.
Imagine that I take the straightened paperclip and fold it in 3 then I magnetise it end to end. Then I straighten it. I have a bit of wire that goes NS NS NS and, in the middle, there's no pole so it wouldn't attract the other wire.

Technically there's the fact that the magnetic field round the magnetised one is a form of stored energy so, from E=MSC^2 it must have a slightly greater mass.
If I drop them near eachother then the magnetic field will make them attract eachother. As they fall then they will tend to move together but the heavier (magnetised) one will deviate less from a straight line than the unmagnetised one. I doubt that this effect would actually be measurable.
« Last Edit: 12/08/2007 15:19:01 by Bored chemist »

#### ukmicky

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« Reply #10 on: 13/08/2007 02:57:41 »
Quote
oooh, Essien has just scored.
Wicked Goal

__________________________________________________________________

Test them by touching them together to make sure one is magnetised .

Then pick one up and throw it hard  against the ground as hard as you can .

Pick it up and touch it against the second paper clip

If it picks it up as easily as before then the one you chucked against the floor isnt the one that was magnetised.

Or if thats wrong you could heat one of them up by pulling it backwards and forwards between two fingers as i believe heat will cause the one thats magnetised to lose some of its strength .

The paper can be used to mark out how strong the magnetised clip is.

« Last Edit: 13/08/2007 03:19:42 by ukmicky »

#### ukmicky

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« Reply #11 on: 15/08/2007 22:17:49 »
SO AM I RIGHT OR WRONGGGGGG

#### lyner

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« Reply #12 on: 17/08/2007 11:06:36 »
Quote
I think Lightarrow's solution is the best but both solutions neglect the idea that you can magnetise a straightened paperclip so that it has a South pole at each end and a North pole in the middle.
No problem here.
If you are holding the non-magnetised clip you will detect SOME difference in force as you move along the magnetised one - whatever arrangement of NSSN NSSNNS  etc you use. There will be 'nulls' along it, somewhere.
On the other hand, the force between the end of your magnetised clip and any part of the unmagnetised one will be the same.

#### lightarrow

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« Reply #13 on: 18/08/2007 21:53:01 »
Quote
I think Lightarrow's solution is the best but both solutions neglect the idea that you can magnetise a straightened paperclip so that it has a South pole at each end and a North pole in the middle.
No problem here.
If you are holding the non-magnetised clip you will detect SOME difference in force as you move along the magnetised one - whatever arrangement of NSSN NSSNNS  etc you use. There will be 'nulls' along it, somewhere.
On the other hand, the force between the end of your magnetised clip and any part of the unmagnetised one will be the same.

#### lyner

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« Reply #14 on: 19/08/2007 00:00:07 »
Thank you kind sir!