Activity #1

Capacitance Measurements for Parallel Plates

The unit of capacitance is the farad, F, named after Michael Faraday. One farad is
equal to one coulomb/volt. As you will demonstrate shortly, one farad is a very large
capacitance. Thus, actual capacitances are often expressed in smaller units with
alternate notation as shown below:

Sometimes the symbol m is used instead of µ or U on capacitors to represent
10^-6, despite the fact that in other situations m always represents 10^-3!

Note:

Equipment:

2 sheets of aluminum foil (12 cm x 12 cm), Pages in a "fat" textbook (or a
thick pad of paper), A digital multimeter (w/ a capacitance mode); 2
insulated wires, stripped at the ends, approx. 12" long, A ruler with a
centimeter scale

You can make a parallel plate capacitor out of two rectangular sheets of
aluminum foil separated by pieces of paper. A textbook works well as the separator for
the foil as you can slip the two foil sheets between any number of sheets of paper and
weight the book down with something heavy and non-conducting like another
massive textbook. You can then use your digital multimeter in its capacitance mode
for the measurements.

• You may need to insert short wires into the capacitance slots of the meter
  to serve as "probes". Do not let these wires touch and "short out".

• When you measure the capacitance of your "parallel plates", be sure the
  aluminum foil pieces are arranged carefully so they don't touch each
  other and "short out".

Edited by RGF and VPC for use at UNL, 10/2/97

© 1990-93 Dept. of Physics & Astronomy, Dickinson CollegeSupported by FIPSE (U.S. Dept. of Ed.) and NSF

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