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Experiment 8 - Capacitance and the Oscilloscope

Experiment 8 - Capacitance and the Oscilloscope - Eric...

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Eric Chong PHYS C1493 Partner: Albert Lee Lab Date: November 16, 2006 Experiment 8: Capacitance and the Oscilloscope Introduction In this lab we use different components of an electrical circuit to investigate the behavior of a capacitor as it charges by some current I provided by a battery source of some voltage V , for varying levels of the capacitance C given in units of μF . We also observe its discharging and relate the values of the time constant τ of both procedures, using the equations RC τ = and 0 log log log e I I t RC = - where by plotting the base-10 log of the current values recorded at certain time intervals t , and plotting these against each other, the linear estimation will give us a slope that allows us to calculate RC with errors. The time constant values for varying levels of the capacitance are found and compared, for the processes of discharging and charging. The second part of this experiment requires the use of an oscilloscope to gauge the value of the time constant τ = RC of a short RC, and compare the mathematically calculate value of this time constant and the value given by the oscilloscope. Sources of error are discussed at the end of this lab. Procedure Large RC Charging For this part of the experiment, we set up circuit elements that comprise the large RC, and for different values of the capacitance in increments of 10 μF , we observe the current I in the system as the capacitor bank charges at regular time intervals. The circuit was connected using a capacitor bank, a power supply, a 10 kΩ resistor, and a switch used to complete the elements in the circuit and to dictate when current should flow to charge the capacitor. We expect the current to be a decreasing function of time as I in the system should decrease as the capacitor charges to completion. Before starting each new trial (multiple trials were enacted for each capacitance level) the switch should be momentarily flipped so that any charge in the capacitor is released across the resistor so as to be able to observe the capacitor charging from its initial state. Values of I were recorded in time intervals of 2 seconds , for capacitances of 10, 20 and 30 μF . Large RC Discharging This procedure was similar to the charging procedure above, accept this time we observed the discharging of a capacitor for the same values of capacitance, 10, 20 and 30 μF . The switch is flipped such that the capacitor is allowed to charge to completion, and once charged, the switch is flipped again to allow us to view the current of the system as it discharges through the ammeter. Values of I are again recorded in intervals of 2 seconds through the ammeter, and these values are taken in multiple trials for each level of capacitance.
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