Est. 1998 — 27 years of woodworking knowledge
Friday Puzzler -- Magnets
alexy
You are in a room with no ferrous objects except two iron bars. These bars are identical except that only one is magnetized. You need to find out which one is magnetized.
One solution is to suspend both bars from the ceiling so they hang horizontally and see which one aligns itself in a N/S orientation.
Looking for [at least] two additional methods for identifying the magnetic bar.
Re: Friday Puzzler -- Magnets
John Veerkamp
rub your hair with synthetic cloth. then pass the bars near your head. the magnetized one will be evident.
I don't know
alexy
Very creative, and one I didn't think about (for reasons that might be obvious if you saw a picture of me!)
But I'm not sure that works. I tired it with the hair on my arms, and got no reaction. I don't think that the ELECTRICAL charge and attraction that attracts your hair to the cloth that you rubbed it with has any reaction to the MAGNETIC attraction of the iron bar. But we need someone whose knowledge of physics is fresher than my 47-year-old recollections!
Hint
alexy
A physicist and a logician gave two different answers to this one.
Re: Hint 2
Alex Y
The logician's answer is based on the statement of the problem, with no particular knowledge about magnetism
The physicist's answer is based on the magnetic field created by a bar magnet.
Re: Hint 2
Larry Barrett
Maybe the physicist has a diamond ring (or some other non-ferrous object that is harder than steel) and knocks a few 'filings' off each bar. Then sprinkle the 'filings' from one bar near the end of the other bar and observe the result.
I don't know if the 'filings' from a magnetic bar remain magnetic, or not.
Re: Hint 2
Alex Y
That might work, but definitely more work than is needed.
Re: Friday Puzzler -- Magnets
Henry Higginbotham
Taking a stab here, without credentials in either physics or logic.
Touch the end of one of the bars (let's call it A) to one end of the other (B) and slide it toward the other end. If there is a magnetic pull that doesn't vary, then A is the magnet. If the attraction dies out at the middle and picks up again toward the opposite end, B is the magnet.
I considered this a couple of days ago but hesitated while I looked for a couple of bar magnets to test it. I never found any, and may not remember much about magnetic fields, so I wouldn't put money on it.
And since the problem stated no other ferrous objects, I wonder if there's some solution involving eddy currents in some nonferrous metal found in the room. But a logician wouldn't be expected to know much about that, so . . . .
Bar magnets, physicist's answer
Alex Y
You nailed it! A bar magnet has magnetic fields of opposite polarity at either end, but none in the middle.
Now for the logician's answer??
Big Hint re Logician
Alex Y
Reread the original problem statement, and see if the logician might be able to simplify the method given.