Resistivity in Play-Doh: Time and Color Variations

Abstract

T he study of electricity and magnetism is fundamental to all first-year physics courses. Developing simple electricity laboratory experiences that are open ended and inquiry based can be difficult. We wished to create a lab experirnent where the students have some control over the experimental design, data atialysis is required, and students investigate the concept of resistivity as found in Halliday Resnick, and Walker.' This experiment uses modeling clay or Play-Doh™ to demonstrate the properties of ohmic materials and resistivity. We were familiar with the paper "Resistance Measurements on Play-Doh"^'" by Jones'^ and we have worked to more accurately explain the physics of the experiment. We have also further developed the experiment to better understand how the resistivity of Play-Doh changes with time. This lab is an exciting, fun experiment that connects a new concept with a familiar childhood toy.Applying a voltage difference (V) across a conductor and measuring the current (/) flowing through a resistor allows the resistance (R) of the conducting material to be determined. This relation is the familiar Ohm's law. V=IR.(1)Most students find the concept of Ohm's law understandable; however, many students are not aware that while Ohm's law holds true for a number of cases, it is not universal.^ A plot of voltage versus current allows the slope, which in this case is resistance, to be determined. For such a plot, a wide range of currents and voltages results in the V//relation being linear. When V7/becomes nonlinear, the resistor ceases to obey Ohm's law and the resistor material is said to be nonohmic. In the measurements of the resistivity of Play-Doh, great care was taken to utilize the full range of voltages where the modeling clay remains an ohmic material.In order to determine the resistivity of a material, the resistor's cross-sectional area A and the length L must be known. The resistance of the material is given bywhere p is the resistivity of the material. The resistivity, measured in units of Om, is a constant for each material at a constant temperature.The dependence of resistivity on area and length can be demonstrated by using conductive paper and conductive ink. Two-dimensional conductors of varying lengths and widths can be created on conductive paper. Measurements of the resistance of the conductive ink can be performed and students can begin to establish the relation between the resistance and the length and width of a conductor.Measurements of resistivity can be complicated, and there are a limited number of materials that can be varied in width and length to experiment with resistivity changes. Play-Doh represents an easily shaped material that can be manipulated to provide various lengths and cross-sectional areas.Substituting Eq.(2) into Eq. (1) yields the values needed to determine the resistivity of any material. Solving for p, we find P = VA ILThe experimental setup for measuring the resistivity of any material requires only a voltage source, an ammeter, a voltmeter, and electrode te...

Investigating the properties of conductive clay and examining its potential as a teaching material

“…Therefore, to use conductive clay as a learning material, in experiments, it is necessary to adjust the salt content and make clay that has an appropriate electrical conductivity according to the application. However, although there is a report on the temporal change in electrical conductivity [9], there are no quantitative reports on the relationship between the salt content and electrical conductivity. In addition, no example specifies the substance that becomes the charge carrier in conductive clay.…”

Student and Professor Collaboration to Develop a First Year Electrical Engineering Capacitance Laboratory with Common Materials

“…al. [2]. The thinking in including it in the activity originally was that the Play-Doh would act as a leaky dielectric, which might provide a good way to introduce the non-ideal properties of capacitors to students.…”