Physics Problems

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Interesting and inexpensive experiments for high school physics.
Joe Wolfe1, School of Physics, The University of New South Wales, Sydney.

Input and constraints. This set of experiments responds to requests from teachers of physics in the state of New South Wales for experiments to address some areas in the new syllabus. Given that one wants to have several sets of gear so that studentscan work in small teams, the implicit budget constraint is severe. We have tried to respect that. Some of the components will be in labs (rulers, watches), others may be readily bought or borrowed (eg transistor radio), others are readily and cheaply available from electronics or hardware stores. A few (transformer cores, transformer windings) are more difficult to buy in small quantities, but areavailable relatively cheaply in bulk. The NSW syllabus requires students to use electronic data collection. This is also a good idea. Most of these experiments therefore use a computer for data acquisition. Computers and sound cards as oscilloscopes. Most schools have several computers (even if they're not in the physics lab.) Further, old computers are very cheap and may be acquired by donationor by bidding at auctions. Nearly all computers built in the last several years have a (stereo) sound card whose input side is a pair of reasonably high quality analog to digital converters (ADCs). Input to the ADCs is via a stereo miniphono jack into a socket usually marked with a microphone icon, or another marked 'line'. The manufacture of sound cards is not standardised, but: Typicalspecifications: Sample at rates including 44.1 kHz, both channels. Range about −1 V to +1 V. Sensitivity to rather better than mV with reasonable linearity. The line input can withstand several volts without damage. The microphone input has a preamplifier that is also fairly robust. The range of your card can be tested by inputting a sine wave and gradually increasing the amplitude until clipping(flattening of the extrema in the oscilloscope display) occurs. Frequency range 20 Hz to several kHz. The high frequency limit is not a problem unless one would like to observe radio signals directly. The low frequency limit is a nuisance in some applications, but not in those described here. Because of the variability in manufacture, there is no preset voltage calibration, but this can easily be done withan oscillator and an oscilloscope or multimeter. Free software for displaying voltage as a function of time and frequency V(t) and V(f) display is available from the net. These are quite powerful: you get a storage CRO, plus a spectrum analyser, plus editing and some averaging facilities. Understandably, the commercial versions are more powerful. We encourage fair use of shareware. Freeoscilloscope software downloads from http://polly.phys.msu.su/~zeld/oscill.html. It requires a 80486 or higher PC running Windows95 or later, or there's an older Windows 3.x version. Free recording and editing software, which includes V(t) and V(f) functions among much else, is available from http://www.syntrillium.com/cooledit/ The free download is adequate for the experiments described here. It requiresWindows 95/98/ME NT/2000/XP
1 With many thanks to Gary Keenan, Jason Whittaker, Tamara Reztsova, Pritipal Baweja, Ken Jackson, Attila

Stopic and John Tann who built sets of the equipment described here for a high school teachers' workshop held at the University of New South Wales in November 2002 .

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Some experiments for high school physics. Joe Wolfe, Physics, UNSW.www.phys.unsw.edu.au/hsc

Both software packages have cursors for measuring parameters and intervals on the display. This is a powerful feature and is included in virtually all modern electronic instrumentation, so it is worthwhile becoming familiar with it. PC sound card → Oscilloscope conversion kits are not absolutely necessary for the experiments described here. The input of the sound card may be used...