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Unformatted text preview: University of Pennsylvania EF. 1 The Electric Field Goals of this lab • understand the relationship between the electric field and lines of force • create and interpret equipotential maps • explore the characteristics of the electric field produced by different arrangements of electrodes Overview In this experiment you will study the electric field (and associated equipotential curves) present in a two-dimensional medium when an electric current flows through it. The basic experiment is illustrated in Figure 1 , which shows the low resistance electrodes embedded in the high resistance conducting medium, and some possible current paths connecting the two electrodes. The situation is similar to currents in a wire, except that in the case of a wire the current is confined to the wire whereas in the geometry of this experiment the current paths spread out from one electrode and converge on the other. Figure 1 An electric field exists at every point in the conducting medium and, using a generalization of Ohm's Law, one can show that the direction of the electric field is at every point the same as the direction of the current. Thus, the paths sketched in Figure 1 can be equally well regarded as the lines of force of the electric field. In the presence of an electric field an external agent must do work to change the position of a charged particle. The potential difference between two points is defined as the work done against the field in moving a unit positive charge from one point to the other. There are curves on which the potential is constant and a charge may be moved on these without doing work, these curves are called equipotential lines. These equipotential lines are necessarily at right angles to the lines of force. If the equipotential lines can be mapped, the lines of force can be obtained by drawing a series of curves which cross the equipotential lines at right angles. University of Pennsylvania EF. 2 This week's lab involves making a map of electrical equipotential lines. Because we are most familiar with gravitational forces, a map of gravitational equipotential lines may be more understandable. These gravitational equipotential maps are called topographic contour maps. On a topographic contour map, contour lines are lines of constant elevation. The analogy is good because when viewed from above, a ball on a hill would behave just like a point charge near a like (and therefore repulsive) charge with the same potential map. When released, both would move from one potential line to the next along the shortest possible path, which is at right angles to the...
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- Spring '09
- Topographic map, University of Pennsylvania, equipotential curves