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An Innovative Inquiry-Based Experiment on the Temperature Dependence of the Resistance of a Filament Lamp Abstract

We have developed an innovative inquiry-based student laboratory activity dealing with the temperature dependence of the resistance of a filament lamp. This introductory experiment is appropriate for a second semester general physics laboratory. The hands-on, active learning laboratory experiment utilizes simple, inexpensive equipment to facilitate student learning of various direct current circuit concepts. The activity builds upon the results of previously published physics education research.

Students perform a transient measurement of the current-voltage characteristic of a lamp in series with a charging (or discharging) capacitor. From the data students calculate the resistance and power dissipated in the lamp. Under normal operating conditions, i.e. the filament glowing brightly, the resistance-temperature characteristic of the filament is seen to exhibit power-law behavior.

I. Introduction

We have redesigned our general physics laboratory to incorporate inquiry-based experimentation into the laboratory experience of our students.1 We believe that this approach leads to improved student outcomes. We have recently compared the performance of a broad cross-section of our students with those published in a national study.2 Our results indicate that our students perform slightly better than the national average.3

In one laboratory experiment, students measure the current-voltage characteristic, and thereby the resistance, of an incandescent lamp. They are provided with the usual definition of resistance, R ≡ ∆V /i, and also with Ohm’s Law ∆V = iR, where ∆V is the voltage difference across the resistor and i is the current. In the first activity, students design a circuit to measure the resistance of a #40 lamp and determine if the lamp obeys Ohm’s Law. The #40 lamp is a miniature threaded-base incandescent flashlight lamp rated at 125mA at 6.3V. By using from one to six lamps in series, students are able to generate a current-voltage characteristic of a single lamp. They are generally surprised to find that the graph is nonlinear and that the resistance of the lamp is a function of the current.

In a subsequent experiment, students obtain quantitative data for the charging and discharging of a capacitor through a #40 lamp. The lamp is placed in series with a capacitor and an experiment is conducted to study the time-characteristic of the current through the capacitor, as well as the current-voltage characteristic of the lamp in a dynamic context. In a previous paper, we presented a numerical model that accurately described the time-varying characteristics of the current through the capacitor.4 The model was implemented in the introductory laboratory.

In this paper, we study the temperature dependence of the resistance of the lamp using data from the RC circuit experiment. The paper is arranged as follows: In Section II, we give a brief introduction to the theory of RC circuits with varying resistance. We also present a model for the

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Ross, R., & Venugopal, E. (2006, June), An Innovative Inquiry Based Experiment On The Temperature Dependence Of The Resistance Of A Filament Lamp Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--567