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Permanent Magnet: Newsletter Challenge (May 2016)

Posted May 01, 2016 12:00 AM
Pathfinder Tags: challenge questions Magnets

This month's Challenge Question: Specs & Techs from IHS Engineering360:

You have two steel bars. One is a permanent magnet and the other is not magnetized. Without using any tool, meter or instrument of any type, how can you find out which one is the permanent magnet?

And the answer is:

See the figure below. If you arrange the two bars in a T shape by putting the permanent magnet as the top of the T (second figure) and the non-magnetized bar exactly at the middle there is no way the magnet will magnetize the bar, because there is no direct unique pole in contact with the bar. So, there is no attraction between the bars.

On the other hand, if the non-magnetized bar is the top of the T structure, then a clear pole (in the first figure and in this case, it is the south pole) will be in contact with the bar and it will magnetize the bar by creating a North pole in the bottom of the bar and a South pole in the top. Therefore, in this condition the two bars will attract.

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#1

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 12:31 AM

Place the rods with one contacting the center of the other one, and then vice versa....the one with the weaker grip is steel, the one with the stronger grip is the magnet...the magnetic flux will be strongest at the pole end, and weakest in the middle....

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#4
In reply to #1

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 5:33 PM

(deleted here, re-posted below)

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#2

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 12:39 AM

Asumming the magnitization is aligned with the longest axis of the bar, a determination can be made by holding the end of one bar perpendicularly against the midpoint of the other bar.

The end of the magnetized bar will be attracted to the mid point of the non-magnetized bar. The end of the non-magnetized bar will not be strongly attracted to the mid-point between the poles of the magnetized bar.

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#3

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 10:14 AM

We need more challenging challenges...

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#5

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 5:34 PM

Let's make it more challenging. The two bars look and weigh exactly the same, but one is a magnet.

Suppose the two bars are stuck together end-to-end.

Without separating the two bars, how can you determine which one is the magnet?

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#6
In reply to #5

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 6:22 PM

Well, the one that was already a permanent magnet makes the other one a (temporary) magnet.

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#7
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 8:03 PM

Right. So how do you tell one from the other?

If someone stuck them together and handed them to you, how could you tell which was which without separating them?

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#8
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 9:09 PM

Do I have anything else to work with, other pieces of iron, etc? The far end of the un-magnet will have a weaker field than the far end of the magnet.

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#16
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 6:50 AM

Anything you can hold in your hand.

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#25
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 5:50 PM
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#28
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 10:09 PM

Sure. But it might be easier to just get a 2nd magnet.

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#40
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/04/2016 7:44 AM

For the corollary puzzle I posted above (# 5) --

If you had a second magnet, either end (N or S) would stick to the end of the steel bar. But if you placed it near the end of the magnet, one end of the 2nd magnet would be attracted and the other end would be repelled.

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#41
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/04/2016 12:50 PM

We haven't got a 2nd magnet or anything to use - nothing in fact as posed by the OP.

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#42
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/04/2016 1:05 PM

I know. But this was a modified problem. See my comments at #16 and #28.

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#35
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/03/2016 2:35 PM

The Magnet would have a null in the middle and the non-Magnet is just an extension of the pole to which it is attached.

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#9
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 10:24 PM

Take a blowtorch to one of them. If they stop being magnetic then that's the one!

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#36
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/03/2016 3:04 PM

Simple & easy you throw both Iron rods into the sand and whichever one comes up with the most Iron particles all over it that 1 is your magnet. & upon separating them the Iron filings will fall off the non magnetic rod.
And furthermore it said " You have two steel bars. One is a permanent magnet and the other is not magnetized. Without using any tool, meter or instrument of any type, how can you find out which one is the permanent magnet? ",
So as simple as possible answer the question WITHOUT OVER THINKING IT !
Jeez Overly Smart people

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#39
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/04/2016 12:11 AM

If I understood your comments correctly, you want to use sand as a determinator as to which bar is a magnet.

The original question text was as follows, you are not the first (and probably not the last) here to ignore it:-

You have two steel bars. One is a permanent magnet and the other is not magnetized. Without using any tool, meter or instrument of any type, how can you find out which one is the permanent magnet?

So sand or anything else is not allowed to be used to test (that would make it even easier than it already is!), that was specifically mentioned. If it or other items WERE allowed, it would have been a very poor question to my mind, understood?

Assuming even that sand "always" has something like Iron or even Steel particles in its composition, which to me is not an automatic "given" either. I would bet some money that there are sands around without any such particles......stymied!!

You only have two steel bars, one of which is magnetized.

Also, post #5 is an extra from someone else, it is not the original question.

Have great day, but I really doubt that any form of "Druid" could answer this question, which by the way, has (to my mind) been answered correctly at least 3 times already.....

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#10

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 10:33 PM

Rerun.

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#11

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/01/2016 10:47 PM

If a piece of string is permitted, suspend each one fromit's balance point. The magnet will point to magnetic north. the steel bar will spin randomly.

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#12

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 12:21 AM

I can search from a variety of probable ways within the problem space each possible magnet is instanced in, even with little or no point of reference, physical or implied; Of course, I'd love to offer more help in computing your problem but I myself have an extremely limited implied attention span bandwidth and am subject to devastating depression in the absence of preoccupation and connection to other humans. facebook: infinetik

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#13
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 12:32 AM

The psychiatric forum is down the hall in CR22.

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#14

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 4:04 AM

The one which picks up iron filings when poked in the sand is the magnet.

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#15

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 4:28 AM

Take your keys from your pocket and see which bar attracts the key ring.

One of the bars is painted red one end; it's the magnet.

The table they are sitting on has a top held on with steel clips. Hold a bar against a clip...etc

Take the compass that is hidden in the heel of your shoe and put it near a bar...etc.

Using the direction finder app in your smart 'phone place your 'phone near a bar...etc.

Place a washer between the two bars and 'stick' them together. The magnet will hold the washer but not so strongly the other bar.

You are wearing steel toe cap boots, so place one of the bars on the toe....etc.

As the result of trauma you have a piece/s of ferrous metal in your body, place a bar on the spot ......etc.

Your belt buckle has ferrous parts, place a bar on the buckle....etc.

Take one bar to the 'fridge and see if it sticks, open the 'fridge, grab a bevy and see if the bar has any effect on the can when sealed and again after opening. Now that you have an open tinny you must dispose of the contents. Try repeating this experiment with the other bar. Hypothesize why it may be that neither bar is attracted to the tinny and then test the hypothesis again with each bar in turn. Then in order to see if the experiment is robust enough to be repeatable...etc.

Jim :-)

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#30
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/03/2016 3:21 AM

Read the question, no tools, keys or other help allowed.....only the two bars of steel, one of which is a magnet.

Actually, the right answer was posted at least 24 hours ago I believe......

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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/03/2016 9:10 PM

Yes, i know the 'right' answer was posted earlier. I also possess many magnets that have the poles on the sides, not the ends, where that process wouldn't work so i tried to think outside the box. There is a famous story about Niels Bohr and a barometer; https://www.ideaconnection.com/blog/2008/10/a-story-about-a-physics-exam/

Apparently not true but it was my inspiration for much of what i do.

Jim

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#45
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/24/2016 10:03 AM

Bend them (DO NOT SEPARATE) so they lie parallel.

Then rotate one to 90 degs to other, at midpoint. Test strength by rocking (DO NOT SEPARATE)

Do the same with vice versa arrangement (DO NOT SEPARATE)

The steel with the stronger bond when rocking is the magnet.

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#46
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/24/2016 11:33 AM

The correct method, which is really simple, has been posted ages ago.....bar magnets.

Have a great day.

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#17

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 7:41 AM

Testing each bar by holding the end of one against the middle of the other. The magnet will 'stick'

But the added problem of 2 bars joined together, by Usbport #5, needs a bit more thought, but as Rixter asks, what other things do we have to help test.

The idea of hanging it balanced horizontally on a string to see if it points 'north' is one way as already suggested, but this will not tell us which end is the magnet.

In any case, on Rixter's question, if the answer is 'nothing' then we won't have any string.

In any case, on this logic, with nothing to help, how do we know it is a magnet in the first place?

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#18

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 8:04 AM

PS: To my last reply, I've just remembered from my schoolkid days, bar magnets were painted RED the North end, and WHITE on the SOUTH end. That's it!

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#19
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 12:26 PM

Personally, I could never remember the Red/White/North/South thing. For ease of remembering I think the ends should be painted Blue & Grey.

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#22
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 3:07 PM

I have a feeling I will regret asking, but why Blue and Grey, why is that easier to remember?

Mind you, Red and White, might have been a local thing in my school lab, because I can't say I have ever come across it since.

But being first to say the 'Challenge' question might be answered by colour coding was worth a punt. With an additional gamble that they might be 'marked' in some way. Is there an ISO standard to magnets???.

On a slightly more technical note, is steel suitable for magnetising (in a permanent way that is) lighter/heavier than ordinary steel. I don't know, but judging the weight might be the answer

Alternatively (back to school) we used a real magnet to rub a piece of steel and that made it into a 'magnet, for a short while. Then rubbed it again with the opposite end of the real magnet - which (sort of) un-magnetised it.

So the bar that is not a magnet after a while is the steel one - which with nothing to test it with - the one that 'sticks' to the middle of the other is the magnet- But we could try that test with the origiinal ones without out trying to magnetise anything.

But again, without anything to test the 'joined-together' ones, how do we know it is a magnet?

It would be useful for the OP to tell what is available as well as telling us what is not available. Then for people like me (with limited knowledge of the subject, we might be able to work it out.

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#26
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 7:14 PM

american civil war. north was blue, south was gray

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#27
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 9:05 PM

Quoted from your post.

If you read #15 you will see that i also suggested this. Does this mean that my posts are not read by you? If 'yes' please tell me why not. Do I need to put more effort into my posts? Maybe i express opinions on things i know nothing about?

P.S. the drag and drop of your sentence didn't work. It was the sentence where you stated that you were the first to suggest the end may be colour coded.

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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/03/2016 8:15 AM

Sorry about that.

I read all post - all those OT's seem a bit unfair.

Anyway, I have a memory attention span of a gnat for facts. I have to rely on an embedded knowledge of principles. I remember school things from 70 years ago - but not things from yesterday. Old age is not for sissies.

I could never remember facts and figures long enough to pass an exam, so I have not got a string of degrees to boast. I have to rely on vague memories of principles - which might good for an arts degree - but not BSc's, MSc's,.PhD's etc dealing in established objective facts rather than subjective opinions.

I just hope we are right in the idea of colour coding - but few CR4 members will will know about this post if their OT blocker is switched on, so I have commented in another post to put the record right.

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#23
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 3:54 PM

Red on the North-seeking pole? The south pole of the magnet points north and vice-versa. Not that we need more confusion.

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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 5:10 PM

I don't know. From distant memory the Red end was North. But the little compasses we used to plot lines of force had a N pole that pointed to the Red end of the magnet.

My modern hiking compass has a Green tip that points N. I think it is supposed to glow in the dark. I don't know - I don't do any hiking in the dark - in fact I don't do much in the day either.

I have had another idea about bar magnets - our local pub has one - it draws you in and somehow, for some strange reason, makes you thirsty.

But it is not a problem, a glass of beer soon cures it.

.

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#29
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Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/03/2016 3:18 AM

If the compass "N" was attracted, (which is a "S" pole, which seeks "N") to the magnet red end, then red was a true "N" pole, just as you said.....

Fully correct.....

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#20

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 1:30 PM

Apart from the "school" teachings of balance one bar on e.g. a pencil, table edge, folded piece of paper, a float (on water) or suspend one on a hair, cotton, etc, and the south end of the magnet will point north, while the unmagnetised bar will not "revolve".

However, I think the simplest way is to have one bar on a table and one hand held.
If the magnet bar is on the table you will feel it "pulling" the plain bar from your hand.If the unmagnetised bar is on the table, the magnet in your hand will drag the bar on the table. i.e. the magnet will overcome the friction of the plain bar. (takes a little practice. - oh, to be a child again.)

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#21

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/02/2016 1:45 PM

Take one bar in each hand. Touch the end of one bar to the center of the other bar. If the two bars stick, the one whose end was touching is magnetized. If they don't stick then the one that was touched in its middle was magnetized.

This will work because the magnetized bar will (I am assuming a bit here) have only one N pole and one S pole and they will be at the opposite ends of that bar, so there will be very little magnetic field evident at the center of the bar.

It *could* be that the magnetized bar was magnetized in a very unusual, yet possible, way with N on one side of the bar and S on the other side. In this case one would have to rotate the bar which was touched in its middle to see if the force between two bars changed as that was done, and it might be necessary to repeat the test with the two bars interchanged. But all that supposes a very unusual way of magnetizing the one bar.

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#31

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/03/2016 7:39 AM

HELLO ALL. CORRECTION.

Please note JIMRAT #15 was first to mention coloured magnets.

My input #18 was actually second so my claim to be first was false. Sorry about that. I re-read #15 and it reminded me - my memory has an attention span of a gnat.

But coming in third is Flash in the Pan #18 who trumps us by all by getting a GA.

....was that for Americanising the code to Blue and Grey?

.....which for USA memory seems a good idea (for America) now the logic has been explained.

And JIMRAT gets a a load of OT' for drawing attention to the order of posts. It's an unkind world.

I look forward to the real answer with baited breath.

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#33

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/03/2016 1:30 PM

Simple & easy test; Throw both Iron rods into the sand and whichever one comes up with Iron particles all over it that 1 is your magnet.

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#34

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/03/2016 2:11 PM

The perpendicular approach is the correct way to determine which bar is the magnet and does deal with the diminished lines of flux at the center of magnetism within the bar that is a magnet; The "magnet" will have no preference to where it exerts its attraction to the non-magnet and may stick to the steel at any point on the bar.

The steel bar will display a preference to either side of the magnetic null point and will not stick directly to the point that has a neutral magnetic field.

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Join Date: Jan 2006
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#37

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/03/2016 4:33 PM

I haven't any sand. I suppose I could rub the two together harshly in a way to generate some 'filings'. The would stick to the magnet.

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Join Date: Mar 2009
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#43

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/05/2016 3:12 AM

you live in a steril world!

How you can find out why you infected?

there's no way to find out! .....Without using any .....

is the magnetic field of the earth a tool?

and you can guess ; with a 50% chance

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#44

Re: Permanent Magnet: Newsletter Challenge (May 2016)

05/06/2016 7:41 AM

Please tell us when we are to get the Official answer.

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