The Chemistry of Currency


Dr. Kenneth Lyle, Duke University Department of Chemistryby Gabrielle Hodgins and Dr. Kenneth Lyle, Duke University, Durham NC

The wonders of magnetic ink!

INTRODUCTION

Demonstrating the magnetic ink used in printing US currency has proven to engage audiences of all ages because of its relevance to everyday life.  Nearly everyone has used machines that distribute and/or accept currency but few understand how the machines distinguish between the various denominations.  The key is in the face of each denomination.  Magnetic ink is used in the printing of the currency.  Each denomination has a different face and, therefore, a different magnetic signature.  Similar to a bar code reader, the machines recognize the denomination by its magnetic signature.  A strong magnet, such as a neodymium magnet, can be used to demonstrate the magnetic character of US currency.

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Focus on Lenz’s Law


photo copy 2by: Ted Beyer

Ahhh, Eddy Current Tubes – you would never think that a hunk of copper pipe and a magnet could make anyone grin from ear to ear. I just love these things. So simple in appearance, and yet so magical to see and use. Whenever I happen to have a set at home, I soon lose control of them to my wife who is just as fascinated by them as I am.ed100_2 2

Although they can be used in fairly high end physics demonstrations, they are stunning enough that everyone who has a chance to see them is simply amazed.

Just realized – you may not have not seen one, have you? Here’s a video for you:

Kinda cool, huh? So, since I have (hopefully) gotten you to say “wow,” I’ll just bet you are wondering “why” — here’s some science:

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Earth’s Magnetic Field


Martin Sagendorfby:  Martin Sagendorf

We recognize heat & cold, dry & damp, light & dark, and sound & silence.  However… I find it absolutely fascinating to consider that we also live within something that we can’t see, hear, touch, or taste.

We all Know:

Our planet has a giant magnet near its core and that its field extends over the whole of the Earth’s surface.  But, do we ever really think about this field that passes through soil, rocks, buildings… and us? Granted, relatively speaking this ‘field’ isn’t particularly strong.  In fact, it’s a rather weak field when compared to those of a horseshoe magnet or, particularly, a modern Rare Earth magnet.

A Great Demo to show Earth’s Magnetic Field:

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Eddy Current Tubes with Video


Ron Perkinsby: Ron Perkins

An eddy current is a current set up in a conductor in response to a changing magnetic field.  Lenz’s law predicts that the current moves in such a way as to create a magnetic field opposing the change; to do this in a conductor, electrons swirl in a plane perpendicular to the changing magnetic field.  Because the magnetic fields of the eddy currents oppose the magnetic field of the falling magnet; there is attraction between the two fields. Energy is converted into heat.

This principle is used in damping the oscillation of the lever arm of many mechanical balances. At the end of the arm a piece of flat aluminum is positioned to move through the magnetic field of a permanent magnet. The faster the arm oscillates, the greater the eddy currents and the greater the attraction to the permanent magnet. However, when the arm comes to rest, the attraction is negligible. Read the rest of this entry »