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Unformatted text preview: e on the computer screen. The image will not appear if the camera is faulty, or there is an issue with the connection. If you have a camera that is not working, you should try the following steps: 1. Quit the VideoRecorder application. 2. Hook up a new Fire-i™ camera to the firewire cable. 3. Launch the VideoRecorder application. If a new camera still does not work, you likely have a bad firewire cable or computer interface card. Contact labhelp@physics.umn.edu and report a bad video setup include the room number and host name of the computer. 197 APPENDIX: EQUIPMENT Adjusting Cameras: To get useful data from the video camera, it is helpful to adjust additional camera settings. The VideoRecorder application has camera controls in the lower left corner that allow you to adjust the exposure value and gain of the camera’s image sensor. The exposure value sets the duration each frame of video is formed. Generally speaking low exposure values have fast discrete images that are appear dark, high exposure values have slow blurred imaged that are bright. The gain amplifies the brightness of the frame and should be adjusted upwards to make discrete darker images easier to see. “Good” camera settings - Motionless objects may look grainy; objects in motion have welldefined edges. low Exposure value (280 or less) high Gain ( about 255) “Bad” camera settings - Motionless objects look nice; motion causes objects to appear blurred without well-defined edges. high Exposure value (default is 511) low Gain 198 APPENDIX: EQUIPMENT ELECTROSTATIC PAPER AND ACCESSORIES: To investigate electric fields with the electrostatic paper, you need to do the following: • Lay the electrostatic paper flat. . • Distribute the pieces of metal (called “electrodes”) on the paper, in the configuration whose field you wish to examine. The tips of the long brass rods may also be used as electrodes, to create point-like charges. • Connect the electrodes to a source of charge. This is done by connecting a wire from the positive (“+”) side of the battery or power supply to one electrode and the wire from the negative (“–”) side to the other as shown in Figure 1. • You may wish to place a wooden block on top of the brass rods to increase contact pressure with the paper. This can increase the magnitude of the electric field created on the paper. It also helps to place an extra sheet of paper under the electrostatic paper. Figure 1: Electrostatic paper Setup Figure 2: Electric Field Probe To measure the electric field from the charged electrodes, you will use a probe connected to a digital Multimeter set to measure volts (see Figure 2). For best results, turn the DMM to measure in the twovolt DC range, as indicated in Figure 2. D-3 199 APPENDIX: EQUIPMENT THE DIGITAL MULTIMETER (DMM) The DMM is a common piece of lab equipment that can be used to measure various electrical quantities, most often current, resistance, and potential. The DMM’s you will be using are capable of measuring both “direct current” (DC) and “alternating current” (AC) circuits. Be careful about knowing which type of measurement you need to make, then set your DMM accordingly. Some DMM’s might be slightly different from the one pictured to the right. Display 13.6 V AC Voltage Range V~ OFF V Selection Dial A Probe Sockets V COM 200 mA DC Voltage Range Resistance Range Current Range 10 A The DMM can measure currents anywhere from 10 amps to a microamp (10–6 amps). This versatility makes the DMM fragile, since measuring a large current while the DMM is prepared to measure a small one will certainly harm the DMM. For example, measuring a 1 ampere current while the DMM is on the 2 milliamp scale will definitely blow a fuse! If this happens, your instructor can change the fuse. However, if you damage the DMM beyond repair, you will have to finish the lab without the DMM. Measuring Current: 1. Set the selection dial of the DMM to the highest current measurement setting (10 amps). Insert one wire into the socket labeled '10A' and a second wire into the socket labeled 'COM'. 2. Attach the DMM into the circuit as shown below: To measure current, the DMM must be placed in the circuit so that all the current you want to measure goes through the DMM. 3. If no number appears while the DMM is at the 10A setting, move the wire from the 10A socket to the 200mA socket and then turn the selection dial to the 200 milliamp (200m) setting. If there is still no reading, change the dial to the 20 milliamp setting, etc. 200 APPENDIX: EQUIPMENT 4. When you have taken your measurement, return the DMM selection dial to the highest current setting (10 amps) and move the wire back to the 10A socket. Measuring Voltage: 1. Set the DMM selection dial to read DC volts ( ). Insert one wire into the socket labeled 'V?' and a second wire into the socket labeled 'COM'. 2. Set the selection dial of the DMM to the highest voltage measurement setting. Connect the two wires from the DMM to the two points between which you want to measure the voltage, as shown below. To measure volta...
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