1202_LabManual.pdf

# E xploration warning a short circuit is what happens

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E XPLORATION WARNING: A short circuit is what happens any time a very low-resistance path (like a wire, or other piece of metal) is provided between points in a circuit that are at different potentials, like the terminals of a battery or power supply. Short circuits can destroy equipment and injure people! Always avoid short circuits in other circuits! Short circuits damage equipment by causing larger currents in a circuit than they are designed for. Only apply the short circuit for a small amount of time . Build the test circuit and make sure all of the bulbs light. Try touching a wire to make a short circuit for a very small amount of time. Determine the shortest time necessary to make a reliable observation of the bulb brightness. Use this technique to make your measurements. Read the section on using the DMM in the appendix. Pay special attention to the connections and settings that are used to measure voltages and currents, and why the DMM should be connected in the circuit differently for voltage and current measurements. Do you know why we should connect them in these ways? Decide how you will insert a DMM in your circuit to measure the current from your battery. Make sure the DMM has the correct setting before you put it in the circuit to prevent damage to the meter. Does the DMM significantly affect your circuit? Look at the brightness of the bulbs before and after you insert the DMM. Determine how long you will need to keep a short circuit connected to make an accurate measurement with your DMM. Decide on the best way to make the set of measurements that you need. 53

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SHORT CIRCUITS – 1202Lab2Prob5 M EASUREMENT Follow the measurement plan that you decided upon in the Exploration section using the reference circuit for brightness comparisons and the DMM for current measurements. A NALYSIS Examine your circuit diagrams for the three bulbs with each short circuit and compare the brightness of the bulb in each situation. Estimate how well you can determine relative bulb brightness. Does this qualitative brightness determination agree with your quantitative current measurements? Does the resistance of your DMM affect the current measurements in each case? Does introducing the DMM to measure the current through a bulb have a noticeable effect on the brightness of that bulb? Estimate the size of this effect. C ONCLUSION Did your predictions match your observed results? Explain your answers. What effects might such malfunctions have on human patients? 54