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# Curriculum and Labs for Engineering Education

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## myDAQ homework problem: Transient Circuits > First-Order > RC Natural Response

Problem Statement: Both pushbutton switches are normally open. Consider this scenario: (1) Begin with both switches open, (2) close switch S1 long enough to charge the capacitor to its initial voltage of 5 volts and then open switch S1 again, and then (3) close switch S2 for a long time beginning at time t = 0. As the capacitor discharges vC(t) passes through two voltages of interest: 90% of its initial value and 10% of its initial value. Determine the time interval between the 90% and 10% voltages of vC(t).

Analysis:

myDAQ Measurement:

• Use jumper wires if you do not have pushbutton switches available
• Make certain to use proper polarity for the electrolytic capacitor
• Display the capacitor voltage vC(t) with the NI ELVISmx oscilloscope
• Use the cursors to measure the time difference between the 90% and 10% voltages
• Follow along with the video clip below to confirm correct operation of your measurement setup and to learn recommended procedures to operate the oscilloscope for a suitable display:

Comparison:

• Report percentage difference between calculated value and corresponding measured value
• Include screenshots of the oscilloscope  display with cursors showing the measured time difference
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