Lab 10 Leyden Jar.pdf
Lab 10 –Leyden Jar: PurposeStudents will build and experiment with a simple capacitor.TheoryThe Leyden Jar(“LIE-den”) was the first effective capacitor. Itholdscharge via polarization of atoms in the non-conductive jar walls onceit’sinduced thereby a voltage difference between the inner and outer conductive layers. The chargingterminalconnectedtothe jar’s internal conductor must be very smooth because pointy surfaces leak charge rapidly via coronal discharge. Figure 10:A classic Leyden Jar in cut-away.This activity uses the electrophorus and pith-ball pendulum from before.Procedure1.Find a bottle or jar made of glass or plastic and fill it with tap water, as this is a decent interior conductive body.2. Wrap the lid very smoothly in foil, and drape some around inside the lid and down so that when the lid is lightly threaded on, foil touches the water. If the foil is unavailable, a nail can be driven through the lid from the top so that the point sticks down into the water.3.If available, wrap the whole jar in foil up to about 2cm of the lid. It is very important that the exterior foil does not touch the lid. If the foil is unavailable, the bottle must be held in one hand when the charge is applied to the lid metal to act as the exterior conductor.4.Using an electrophorus, charge up the Leyden Jar by touching the charged electrophorus plate to the lid’s metal (meaning the foil on it or the nail).5. Without accidentally touching the lid metal and discharging the jar, try to use the lid metal to power a pith-ball pendulum: Lid metal on one side of it, finger on the other, very close but not touching. Oscillation of the pendulum between the two means it works.6. Assuming success up to this point, try to charge the jar, wait five minutes, and test it. Then try an hour. A well-designed Leyden Jar (much better than this one) can hold a charge for months!AnalysisAnswer the following on Canvas via complete, grammaticalsentences:1.Why is the outer conductive layer helpful when charging the jar? It isn’t even in contact with the lid and water! 2.The simplest general equation for the capacitance(effectiveness holding a charge) of a capacitor isC=εA/z. The three variables are: ε, the permittivity or polarizability of the insulating layer (in this case the glass or plastic); A, the total area of either conductive layer in contact with the insulator; and z, the thickness of the insulating layer: What are the three ways to improve a Leyden Jar, in theory, based on this equation?
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