Physics Puzzle: Magnetic Attraction
August 30th, 2008
| Categories: Electricity and Magnetism, Physics Puzzles
Here’s a physics puzzle even non-physicists can attempt: you are given two identical bar magnets, like the one shown in the picture below, except for one being a fake - just a piece of unmagnetized iron - and the other being a real bar magnet (remember, they have two “poles”, traditionally called North and South). How can you tell which is which, without using any equipment other than your ingenuity and the bars themselves?
Aww… You gave such a big hint here…
(remember, they have two “poles”)
Take one of the bars and touch its end to the middle of the other bar. The magnetic effect will be strong on the ends of the magnet but weak in the middle. Therefore, if you touch the end of the magnet to the middle of the nonmagnetized iron bar, the attraction will still be strong but the attraction will be weak if you touch the end of the nonmagnetized rod to the middle of the magnet. You can tell between strong and weak attraction if necessary by switching rods.
That was so easy…
Btw, you still haen’t answered my question that i’d mailed you abt…
Monsieur physicist, you’ve won.
Here is a long overdue solution to the problem posted. Sanket got it right. The magnetic attraction is proportional to the gradient of the magnetic field, which is minimal at the middle of the magnetized rod and strongest at its tips. The field lines of a bar magnet can be seen on Wikipedia:
http://en.wikipedia.org/wiki/Image:Earths_Magnetic_Field_Confusion.svg