High voltage supplies are often used in physics classes for demonstrations and laboratory work. These devices deliver several thousand volts DC, while limiting the current to a safe level, typically under 5 mA. One issue with these power supplies is their expense, which means schools may not have one. Less expensive homemade units have been discussed before, but here we present an inexpensive, off-the-shelf substitute, namely electric bug zappers, which can do nearly the same thing as the more expensive supplies, and we connect it to an easy-to-build Franklin’s bells setup that is suitable for measuring the current shuttling across it.
References
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See, for example, Consortium of Local Education Authorities for the Provision of Science Services (CLEAPSS) Student Safety Sheet 10 – Electricity, available at http://science.cleapss.org.uk/Resource/SSS010-Electricity.pdf.
3.
See, for example, the Unilab Battery Top EHT Supply, currently £156 from Phillip Harris, https://www.philipharris.co.uk/product/physics/electricity-and-magnetism/circuits/battery-top-eht-power-supply/b8h28305, accessed on June 1, 2018. We also note plug-in high voltage supplies are often two to three times this amount.
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A video of the LEGO and PCB version of Franklin’s bells shown in Fig. 2 can be seen here: https://youtu.be/PtgDX6agZXE.
10.
Joseph M.
Crowley
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,” Proc. ESA Annual Meeting on Electrostatics 2008, Paper D1
, retrieved from http://www.electrostatics.org/images/ESA_2008_D1.pdf on July 2, 2018. The final result of the paper shows that the capacitance of a sphere near a conducting plane is well approximated by C ≈ 4πε0 R [1 + ln(1 + 1/ξ)/2], where ξ = h/R is the ratio of the spacing between the near edge of the sphere and the plate, h, to the radius of the sphere, R. On this work a typical space between the ball is 4 mm and its radius is 20 mm, which gives a factor of nearly two times the isolated sphere value. But note that this expression is for a sphere and single plane, whereas our Franklin’s bells setup is a sphere at a position between two conducting planes.11.
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2019
American Association of Physics Teachers
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