One of the key properties of metals is that they typically conduct heat and electricity extremely well. There are countless practical applications of conductivity, plus some cool science projects. One of the more interesting projects is shrinking a quarter using electricity. Actually, it doesn’t need to be a quarter, but this coin is large enough that you can see a significant difference in its size after it has been zapped. The diameter of a quarter shrinks so it’s about the same as a dime. Here’s what you do and how it works:
Materials You Need
- coin (or other piece of metal containing a conductive metal or alloy, such as aluminum, copper, or silver)
- heavy-duty wire coil (the heavier the better)
- electromagnetic conductor (seriously strong… like a couple thousand volts)
Let’s Shrink a Quarter!
- Place the coin very close to the wire coil. There should be no contact between the wire and the coin (i.e., close, but not touching).
- Discharge current through the conductor. The best way to do this is using a high voltage capacitor. This produces an extremely strong, quickly oscillating electromagnetic field surrounding the wire coil.
- The electrical field of the coil is associated with an extremely strong magnetic field, which changes the shape of the coin. It’s electromagnetic pressure. The mass of the quarter is unchanged — only its dimensions change. While the quarter is a smaller diameter, it’s thicker. The difference in size depends on the composition of the coin and how much current you run through the conductor.
Note: When you shrink a quarter, it will also be extremely hot! Wait for it to cool down before handling the coin.
How It Works
The quarter shrinks because the set-up applies what is called high-velocity electromagnetic forming (also called EM forming or magneforming). When the technique is used for commercial applications, high energy capacitors are discharged through a coil of wire. The rapidly changing electromagnetic field that is generated acts as a force to change the shape of metal near or inside the coil. The better the conductor, the more effective the process is. The best results are seen with silver, copper, and aluminum, but nickel, steel, and various alloys work to a lesser extent. There is an equal and opposite force to the one pressing in on the coin. This force acts on the coil winding. If the coil isn’t strong enough, it will blow apart. The coils are only good for one attempt.
It’s worth noting a similar effect occurs when a substation power transformer short circuits. The windings of the transformer may blow apart violently.
See a Quarter Shrink from Electricity
A lot of people think the shrunken quarter is a hoax. Discovery made a video of the process. They ran a camera at 100,000 frames per second to try to capture the shrinking process. Here’s how that went.
Not good enough? Here’s another video attempt at 100,000 frames per second, presented by amateur scientists at Hackerbot Labs in Seattle. In this video, you can see the green flame as the copper in the coil they used vaporizes.
So, as you can see from the videos, this isn’t a project you can replicate on your own without a bit of preparation and safety gear. If you do decide to go ahead, Stoneridge Engineering has some tips. They also address whether or not it’s illegal to alter currency.