Phys 132L
Spring 2008
Laboratory 4: Electrostatic Potential and Electric Fields
In one dimension, the electric field and the electrostatic potential are related via
either
V(x1)−V(x2) = −Zx2
x1
Edx(1)
or
E=−
dV
dx .(2)
There are analogous relationships for three dimensional cases. Of the two quantities
the electrostatic potential is far easier to measure and the entire electrostatic potential
landscape can be mapped using a voltmeter. Once the landscape is mapped Eq. (2)
can be invoked to determine the electric field. An important additional rule, inferred
from Eq. (2), is that the electric field points opposite to the gradient of the electrostatic
potential and that these gradients are perpendicular to equipotential lines, i.e. lines along
which the electrostatic potential is constant. The aim of this laboratory is to investigate
these relationships and to exploit them to determine the electric fields produced by
various arrangements of charge distributions.
1 Electrostatic Potentials and Electric Fields: Parallel Conductors
In this part of the experiment you will investigate the electrostatic potentials and
the electric fields produced by parallel conductors. Each conductor, or electrode, will be
connected to one terminal of the output of a power supply.
a) The electrodes will eventually be drawn onto a sheet of conductive paper (black
paper with a grid) using an ink pen that contains silver ink particles suspended in
a solvent. Using a light colored pencil trace, on a conductive sheet, two parallel
lines extending along the length of the sheet and separated by 6cm.The electrodes
will be drawn on top of these lines.
b) When used properly the conductive (silver) ink pen can produce highly conductive
lines. Vigorously shake the conductive ink pen (with the cap on) for 10-20 seconds
to disperse any particle matter suspended in the ink. You should be able to hear
something moving inside the pen while you do this.
c) Drawing with the pen requires simultaneously depressing the tip of the pen and
squeezing the barrel of the pen. Practice doing this on a piece of scrap paper until
you can produce a continuous silver line of approximately uniform width.
d) Draw the electrodes on the conductive paper, following the lines that you traced
earlier. It is essential that the electrodes are continuous; any break will disrupt the
conductivity.
