Customer Solutions

Improving Physics Education Using NI LabVIEW and DAQ

Author(s):

Urs Lauterburg, University of Bern, Physics Institute, Switzerland

Industry:

University/Education

Product:

Data Acquisition, LabVIEW

The Challenge:

Enhancing university-level physics education to provide demonstration experiments, student labs, and physics phenomena simulation.

The Solution:

Improving physics education using LabVIEW-driven NI data acquisition (DAQ) devices on Apple Macintosh computers to create numerous physics experiments, three of which are described in this article.

The Compton Experiment

Demonstration Experiment: Acquiring a Compton Spectrum

The famous Compton scattering experiment is one of the most important experiments that led to the understanding that electromagnetic waves also have particle properties. First conducted by experimenters in 1923, the experiment strongly supports the Einstein quantum electromagnetic wave packets hypothesis. Using the Einstein equivalence principle formula, experimenters assign a mass and, thus, a momentum to the photon. In the Compton experiment, photons are scattered by electrons as if they had a mass. From this effect, experimenters derive the characteristic Compton wavelength.

To demonstrate this effect and explain the multichannel analyzer concept, we built an arrangement of a 22Na radioactive source and two diametrically positioned NaI scintillation counters. The counters detect individual photons, indicating their energy. The photons interact with the NaI material to create weak light flashes with intensity proportional to the photon energy. A   photomultiplier tube detects and amplifies the flashes. The 22Na source emits positrons, which annihilate with surrounding material electrons, each one creating two photons or gamma quanta that are emitted in exactly opposite directions.

With the help of an electronic coincidence unit, we select only those photons resulting from positron-electron annihilation. The pulse energy distribution of one counter represents the characteristic Compton spectrum. To analyze the pulse heights, we trigger the DAQ board analog input channel with the coincidence pulses, via a delay circuit set with a delay to achieve one single data conversion at each energy peak top. For each new incoming pulse height value, LabVIEW scales the amplifier voltage to energy in keV and updates an energy distribution histogram to show the spectrum as it develops and builds itself up.

Student Lab Experiment: Interactive Sound Analysis

In this lab, the students will explore, acquire, analyze, and observe the sounds produced by appropriate large symphonic gong excitations. The goal is to get students acquainted with various sound measurements and digital sampling methods.

Again, a dedicated LabVIEW software application guides the students through the different lab stages. Because the actual sound signals are picked up by a microphone, the students will first calibrate the microphone voltage signal against a sound pressure instrument. After the microphone calibration, the students explore the gong sounds after conversion into the frequency domain. For the amplitude, the students choose from volts, sound pressure, and sound pressure in decibels. Also, the students can view the physiologically weighted frequency spectrum display by calculating the physiological filter function according to the actual measured dB level.

In the first part of the program, the students observe the sound in the frequency domain, helping to find an especially suitable way of gong excitation for further analysis. In the second part of the LabVIEW acoustic application, the system records various sounds on a disk. Students can sample the sound at a chosen rate for the entire sound duration. The system can also save a number of interesting signals to disk in a compact binary format. The third part of the program offers the possibility for a more detailed frequency behavior investigation over the acoustical signal time. The experimenter selects suitable parameters to optimize the analysis for the best possible time and frequency resolutions, while keeping the computer calculation load below a reasonable limit. The system uses joint time frequency analysis algorithms to transform the signal from the time domain into a 2D spectrogram that displays how the frequency components vary in time.

Simulation of Physics Phenomena: Statistical Diffusion Process Behavior

Diffusion is a very fundamental mechanism in nature and is responsible for a great number of important phenomena, such as heat conduction, gas and fluid behavior, and concentration variations effecting electrolytic signal propagation in organic cells. To show this mechanism essence, we simulate a diffusion process as a continuously updated histogram. We start with 2,000 elements in the center bin, then process each element having three random possibilities: staying, dropping to the right neighbor bin, or dropping to the left neighbor bin. This simple property leads to a spreading distribution that is expressed analytically with a widening gaussian probability function. The system shows the LabVIEW simulation result by calculating the positions for every one of the 2,000 particles, graphing the result for every cycle. At the same time, the gaussian distribution function is superimposed on the result.

LabVIEW Provides Student Benefits

LabVIEW is a versatile and powerful tool to be used in physics education. Using the LabVIEW graphical programming, students develop fast and efficient user-controlled applications for measurement, analysis, and data visualization of data, such as

• Controlling demonstration experiments to acquire signals and display them online
• Helping implement dedicated instrumentation for student lab experiments
• Producing interactive simulation programs in appropriate cases

Our 10-year engagement using the LabVIEW graphical programming environment as a standard tool to perform data acquisition, analysis, and display was well worth the initial investment. We saved several times the expenses, which we would have spent on dedicated hardware. Because of the long-term and frequent equipment use, all our LabVIEW applications run on the stable Apple Macintosh platform.

For more information, contact:

Urs Lauterburg

University of Bern, Physics Institute, Switzerland

Sidlerstrasse 5, 3012

Bern, Switzerland

Tel: +41 -31-6314488

Fax:+41-31-6314405

E-mail: urs.lauterburg@phim.unibe.ch