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Laptop-based Data Acquisition

In

Introductory Physics Laboratories

Keith Bonin and Machele Bailey

Objectives:

The goal of this project is to introduce students to computer-based data acquisition techniques and to encourage data analysis using spreadsheets and commercial curve-fitting tools. In addition, we want to demonstrate how the computer can actively interface with experiments, rather than simply be used in a passive data acquisition and analysis role.

Description of Technology Used:

The IBM Thinkpads are interfaced with hardware and software from Pasco Scientific, Inc. an education technology company in Roseville, CA. Hardware consists of sensors for detecting sound waves, light, temperature, electical signals, etc. and signal generating components, including an amplifier that can provide external laboratory equipment with digital or analog signals.

Activities/Procedures:

Physics 113, Fall Semester

The following laboratories have been converted to computer-based laboratories using student laptops and Pasco software, sensors, and interface hardware. The students are encouraged to use the Microsoft Excel spreadsheet for data analysis and plots. At the beginning of each semester, we conduct a session in the week before labs begin (usually a partial week) where we load the Pasco software onto the IBM Thinkpads. We review the operation of the Pasco interface (hardware and software), we show the students how to import Pasco data files to Excel, and we give some simple examples of how to use Excel (like finding the average and standard deviation of a column of data, column manipulation, plotting and fitting data). The students are given a 10 page handout, with figures, that reviews the important points made in the tutorial presentation.

For each lab, there is a writeup in the manual that includes a discussion of the computer interface and operation of the Pasco equipment with the Thinkpad.

Plots of relevant data, and corresponding analytical curves fit to the data, can be printed out by the students in lab on a local printer connected to their computers via the network jacks at each lab bench.

1. Lab 2: Uniform Acceleration. Photogates that detect the passage of a cart moving on an airtrack or the passage of a sphere down an inclined plane can be read by a laptop. A set of time measurements for different distances in each case can then be input into Excel, plotted and fit with an appropriate theoretical curve to check experimental agreement with theory.

2. Lab 3: Measurement of Mass. Photogates attached to laptops can be easily used here as well. An Atwood's machine involving an airtrack is used to determine the unknown mass of an object. Another method for mass measurement is to measure the period of oscillation of a harmonic oscillator whose mass is varied. The periods of oscillation can be measured using laptop-attached photogates. Again, results can be analyzed and plotted using Excel.

3. Lab 6: Conservation of Momentum. Here we again use the airtracks and photogates to verify conservation of momentum and to test conservation of energy. These measurements are readily recorded by the laptops.

4. Lab 9: Harmonic Oscillation. The laptop-attached photogates is used to determine the period of an oscillating cart attached to two springs on an airtrack and it determines the period of a simple pendulum.

Physics 114, Spring Semester

1. Lab 1: Oscilloscope and EKG. A set of Pasco sensors for detecting electrical signals from the heart is readily used to record and display heart rhythms on the laptop screen. This is also the first lab in which the IBM Thinkpad and Pasco hardware is used to generate a signal to run the experiments. The computer system is an active component of the experiment, not a passive data-taking device.

2. Lab 4: Simple Circuits and Ohm's Law. Pasco voltage sensors are used to display the results of measurements on the laptop screen. The laptops record the applied voltage and resulting currents to demonstrate directly agreement of the circuit behavior with Ohm's Law. Again, the Tinkpads are used to generate signals and play an active experimental role.

3. Lab 7: Capacitors. Pasco analog-to-digital converters are used to directly detect and record RC decay in capacitor circuits. Plots of the resulting data and subsequent fits can yield good quantitative results for the natural decay times of the RC circuits.

4. Lab 8: Diodes and Transistors. Again, using Pasco's ADCs we detect and record on the laptops the non-Ohmic behavior of these interesting electrical components. Plots of the I-V curves are easily made using Excel.

In addition to these quite straightforward ways of integrating computer collection and analysis of laboratory data for existing labs, we can redesign or expand some labs in ways to allow the laptops to take and analyze data in these cases. Other sensors, such as force and motion sensors can be used to perform measurements that must presently be done less accurately or with fewer repetitions than could be done with computer integration. For next year we hope to computerize the nuclear counting lab, where a measurement of radioactive decay in time is readily performed and recorded using the Thinkpad and the Pasco interface. Plots of the data and a fitted curve can be generated using Excel to obtain an accurate value for the halflife of a radioactive isotope of barium.

Specific Outcomes:

For the past year and a half, we have run 2 sections (out of a total of 11 laboratory sections) as computer-based. Student surveys were generated at the end of the first semester of the program. The participating students indicated that the computerized laboratories enhanced their learning experience and helped increase their knowledge of the important role computers can play in data acqusition and analysis. However, there is reluctance by some students to sign up for these sections because they are not comfortable with their laptops, because they perceive computer-based labs as taking more time to complete, or they do not want the additional complexity of setting up and running the experiment by computer.

Next year, when the majority of enrolled students will have their own IBM Thinkpads, all laboratory sections will carry out computer-based experiments.