Finding the dependence of capacitance on geometric properties.
a.) Use two equal sized sheets of aluminum foil and a large textbook to make your own capacitor. Use the capacitance meter to find the capacitance of your home-made capacitor. Make different capacitors by inserting between the sheets at least 5 different separations in your textbook (i.e. 30 pages, 60, 90, 120, 150 works well.) Plot capacitance first as a function of number of pages and then as a function of inverse number of pages. How does capacitance depend on plate separation?
Note: before you use the capacitance meter, be sure to zero it. Let the leads (which you are to keep as short as possible—Why?) hang loose and make sure the capacitance meter hovers around zero.
b.) Now re-measure C for your homemade capacitor, but this time, leave the page separation at about 50 pages and step down the size of the sheets by carefully folding them in half, then quarters, then eighths, etc. Plot C as a function of plate area, A. What is the functional dependence?
Now that you have separated out all dependence on the geometry of the capacitor, what is left is a specific property of the material between the plates...in this case your textbook paper. This property is called the permittivity of your textbook paper. Measure the thickness of a large number of pages and find the thickness of a page. Use this value to convert your page spacings into SI. Compute the relative dielectric constant of the paper by comparing your measured capacitance to that expected with air between the plates.
(There may be an additional component that will be discussed during lab.)
Last Modified onFriday, April 12, 2002