lab_32 - LAB# 32 CAPACITORS INTRODUCTION: The charge q on a...

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LAB# 32 CAPACITORS INTRODUCTION: The charge q on a capacitor’s plate is proportional to the potential difference V across the capacitor. We express this with V q C , where C is a proportionality constant known as the capacitance . C is measured in the unit of the farad, F, (1 farad = 1 coulomb/volt). If a capacitor of capacitance C (in farads), initially charged to a potential V 0 (volts) is connected across a resistor R (in ohms), a time-dependent current will flow according to Ohm’s law. This situation is shown by the RC (resistor-capacitor) circuit below when the switch is closed. Figure 1 As the current flows, the charge q is depleted, reducing the potential across the capacitor, which in turn reduces the current. This process creates an exponentially decreasing current, modeled by V t V e t RC ( ) 0 . The rate of the decrease is determined by the product RC , known as the time constant of the circuit. A large time constant means that the capacitor will discharge slowly. When the capacitor is charged, the potential across it approaches the final value exponentially, modeled by V t V e t RC ( ) 0 1 . The same time constant RC describes the rate of charging as well as the rate of discharging. To better understand the principles of charging and discharging answer the following questions. Voltage probe SPDT switch
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1. Consider a candy jar, initially with 1000 candies. You walk past it once each hour. Since you don’t want anyone to notice that you’re taking candy, each time you take 10% of the candies remaining in the jar. Sketch a graph of the number of candies for a few hours. 2. How would the graph change if instead of removing 10% of the candies, you removed 20%?
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This note was uploaded on 02/29/2012 for the course PHYS 227 taught by Professor Rabe during the Fall '08 term at Rutgers.

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lab_32 - LAB# 32 CAPACITORS INTRODUCTION: The charge q on a...

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