Date: Fri, 18 Feb 2011 17:13:35

Author: Jerry DiMarco

Subject: Re: Tin Foil Capacitor


I would expect the single foil rolled up with a dielectric to give
different results from the uninsulated foil, because the dielectric
increases the separation between layers and reduces the electric field
between layers. I wonder too if some charge will be trapped in the
innermost layer.
Rolled foil capacitors such as electrolytics actually hold more
charge than 2 parallel plates of the same size because each foil is flanked
on both sides by the opposite polarity plate, allowing it to store charge
on both sides.
It seems to me it would be more accurate to explain the example of
the conductive umbrella as charge being repelled off the umbrella (on to
the electroscope) as the conductive surfaces come together. There is no
change in surface area, just in surface configuration...


At 2/17/2011 09:19 PM, you wrote:
>It's the last paragraph of the article that has this error. Here's the
>citation from December:
>Tin foil capacitor
>And if it's not bad form to quote the article here:
>...... It might be possible to make another tube that has the foil
>sandwiched between sheets of plastic or paper and then roll up the foil.
>The plastic should insulate the foil layers when it is rolled up, and
>therefore there should be no difference in elec- troscope separation when
>the foil sandwich is unrolled and rolled.


Jerry DiMarco
Manager of Lecture Demonstrations and Instructional Labs
Montana State Univ., Physics Dept.
Bozeman, MT

Our Motto: "A demo a day helps learning to stay"

From Sat Feb 19 08:39:16 2011