A laboratory on the four-point probe technique

We describe how a classic electrostatics experiment can be modified to be a four-point probe lab experiment. Students use the four-point probe technique to investigate how the measured resistance varies as a function of the position of the electrodes with respect to the edge of the sample. By using elementary electromagnetism concepts such as the superposition principle, the continuity equation, the relation between electric field and electric potential, and Ohm's law, a simple model is derived to describe the four-point probe technique. Although the lab introduces the students to the ideas behind the Laplace equation and the methods of images, advanced mathematics is avoided so that the experiment can be done in trigonometry and algebra based physics courses. In addition, the experiment introduces the students to a standard measurement technique that is widely used in industry and thus provides them with useful hands-on experience. (C) 2004 American Association of Physics Teachers.