Electric Fields

Overview

Source: Yong P. Chen, PhD, Department of Physics & Astronomy, College of Science, Purdue University, West Lafayette, IN

An electric field is generated by a charged object (referred to as the source charge) in the space around it, and represents the ability to exert electric force on another charged object (referred to as the test charge). Represented by a vector at any given point in the space, the electric field is the electrical force per unit test charge placed at that point (the force on an arbitrary charge would be the charge times the electric field). The electric field is fundamental to electricity and effects of charges, and it is also closely related to other important quantities such as electrical voltage.

This experiment will use electrified powders in an oil that line up with electric fields produced by charged electrodes to visualize the electric field lines. This experiment will also demonstrate how an electric field can induce charges and how charges respond to the electric field by observing the effect of a charged rod on a nearby soda can.

Procedure

1. Visualize Electric Field Lines

Obtain an electrostatic generator (such as a handheld Static Genecon or a van der Graff generator), a pair of electrodes arranged in a concentric circle configuration, and a pair of electrodes arranged parallel to each other.
Obtain a Petri dish or an observation tank, fill it with oil (such as Castor oil), and add electrified/polarizable powders (such as semolina seeds) in the oil.
Load the electrodes with the parallel electrode configuration onto the obs

Results

For step 1.4, the powder will start to form line patterns between the electrodes as shown in Figure 3. This is because the powders are polarized and will line up with the electric field. They are also attracted toward where the field is stronger, namely closer to the positive electrode. The powders do not move appreciably because the oil is very viscous. The pattern of the powders visualizes the "electric field lines".

Application and Summary

In this experiment, we have visualized electric fields using electrified powders in an oil that align with the electric field lines. We also demonstrated the effect of an electric field produced by a charge rod to attract polarizable objects toward the rod, i.e., the source of the electric field where the electric field is stronger.

Electric fields are ubiquitous. There are electric fields whenever there are charges or voltage (electric potential) differences. Electric fields provide