Science Buddies: "Ask an Expert"

My teacher says that we have to finish our model by tomorrow and I just can't figure out how to light a light bulb with a Leyden Jar and static generator?
How am I to do this, and do I have to us a battery?

Hi,

I do not think you will be able to light an ordinary incandescent light bulb using a static generatorand a Leyden jar, but you might be able to get a neon bulb to flash. The Leyden jar is a condenser and can be used to store a charge. The trouble is that it takes a very high voltage to store much of a charge in one. It can store enough charge at high voltage to give a very nasty shock though, so be warned!

The idea would be to charge up the Leyden jar as much as you can with the static generator. If you then use the leads of a neon voltage tester to connect the two sides of the Leyden jar, you will probably see a spark jump between the lead of the neon light and the Leyden jar, and a flash of light from the neon lamp.

The problem with trying to do the same thing with an incandescent lamp is that it takes a relatively large amount of current at relatively low voltage to light one. The neon lamp takes much lower current, but higher voltage to light. The Leyden jar tends to be charged to very high voltage (thousands of volts), but stores relatively little charge.

Here is a link that may be of interest. It talks about the use of neon lamps near the end of the page:

http://www.tufts.edu/as/wright_center/p ... I_Intr.pdf

I hope this helps. Good luck on the project.

Barrett Tomlinson

Is it possible that a resistor will help?

Also can i directly hook my leyden jar with me flashlight lighbulb and make it flash, because all I get now is a spark at the connected end and the bulb will not light

Hi,

Will a resistor help? A resistor can help slow the rate of discharge of the capacitor, but it also dissipates some of the electrical energy. My best guess as far as will the flashlight lamp light if a resistor is added to the discharge circuit is: No it will not help get the lamp to light.

Can you get the flashlight lamp to light by discharging the Leyden jar through the lamp? I do not think so. As I said in the first post the capacitance of a Leyden jar is too low, a few thousand picofarads typically. If you want to light a flashlight lamp with a capacitor, charge a capacitor of >0.5 farads with a battery, then discharge that through the flashlight lamp. Warning - if you tried to charge a 0.5 farad capacitor up with the static generator and you managed to get to charge up to a high voltage, the energy stored in it could kill you if it discharged through you . We are talking about a capacitor with 10,000,000 or more times the capacity of a Leyden jar.

Good luck with the project!

Barrett Tomlinson