To use the geiger counter in conjunction with the

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Unformatted text preview: at magnets inserted into the side labeled N will be north attracting and vice versa. You need to insert the S pole of the bar magnet into the side labeled N and the N pole of the bar magnet into the side labeled S. 209 APPENDIX: EQUIPMENT MEASURING RADIATION (Geiger Counter) To measure radiation you will need a Geiger Counter. The tube detects incoming radiation (alpha, beta, or gamma decay) and produces a voltage spike which the counter unit records. To use the Geiger Counter in conjunction with the computer plug the connecting cord into the round hole on the right side of the counter, and plug the other end of the connecting cord into the LabPro Interface port labeled “DIG/SONIC 1”. The computer uses the software LoggerPro in conjunction with the Geiger Counter to measure radiation. For a description of the LoggerPro software see Appendix E. To begin measuring radiation amounts the power switch on the Geiger Counter must be moved to the “ON” position, or the “AUDIO” position. The Geiger Counter’s red light will flash whenever it makes a radiation count. When in the “AUDIO” position the counter will also make a beep noise whenever it makes a radiation count. There is a switch on the Geiger Counter that controls its detection sensitivity. The switch has positions labeled 1X, 10X, etc. For the lab problems in this manual the 1X position will most likely be the best setting. Counts recorded by the detector are the result of radioactive decay, which is a randomly occurring event. Events that are the result of random processes have inherent uncertainty. This means that if the count rate for a certain sample is recorded several times, the number of counts recorded will fluctuate around an average. In a set of N counts, if N is small the uncertainty in N will follow Poisson Statistics. If N is large the uncertainty will follow Gaussian Statistics. (These terms are explained in any math reference book, for example see http://mathworld.wri.com). Keep uncertainty in mind when deciding how many counts are "enough" to allow comparisons among count rates under different conditions. 210 Appendix: SOFTWARE MOTIONLAB & VIDEORECORDER -Video Analysis of Motion Analyzing pictures (movies or videos) is a powerful tool for understanding how objects move. This appendix will guide a person in the use of VideoRecorder and MotionLab to analyze motion. LabVIEW is a general-purpose data acquisition programming system. It is widely used in academic research and industry. Later you will use LabVIEW to acquire data from other instruments. Using video to analyze motion is a two-step process. The first step is recording a video. This process uses the video software to record the images from the camera and compress the file. The second step is to analyze the video to get a kinematic description of the recorded motion. MAKING VIDEOS – USING VIDEORECORDER After logging into the computer, open the video recording program by double clicking the icon on the desktop labeled VideoRECORDER. A window similar to the picture below should appear. You should see a "live" video image of whatever is in front of the camera. By adjusting the lens on the camera, you can focus the sharpness of the image as necessary. The controls are fairly self-explanatory; pressing the Record Video button begins the process of recording a video. While the video is recording, the blue Progress bar beneath the video frame shows the fraction of the video recorded. Once you have finished recording, you can move through the video by dragging the Frame Number slider control. If you are not pleased with your video recording, delete it by pressing the Dispose button. 211 APPENDIX: SOFTWARE You might notice that the computer sometimes skips frames. You can identify the dropped frame by playing the video back frame by frame by clicking the arrow above the frame number. If recorded motion does not appear smooth, or if the object skips irregularly, then frames are probably missing. If the computer is skipping frames, speak with your instructor. While you are recording your video, you should try to estimate the kinematic variables you observe, such as the initial position, velocities, and acceleration. The frame number is shown in the VideoRECORDER window, in the box below the Frame Number slider. With the frame number and the fact that the video has 30 frames per second, you can use known lengths for objects in the video to estimate kinematic variables. These values prove very useful for your prediction equations. Be sure to record your estimates in your journal. Once you have recorded a satisfactory video, save it by pressing the Save Video button. You will see a Save window, as shown here. To avoid cluttering the computer, you will only be able to save your video in the Lab Data folder located on the desktop. In the File name box, you should enter the name that you wish to give to your video. This name should be descriptive enough to be useful to you later. 212 APPENDIX: SOFTWARE ANALYS...
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