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| Topics: Capacitor, capacitance, square-plate
capacitor, electric field, electrostatics. Pre-requisite skills: Basic understanding of electrostatics. Approximate completion time: Under an hour. |
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Provide sufficient detail to verify that the assignment was completed in a meaningful manner. |
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Applet by Wolfgang Christian |
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| 1. Select Capacitors 1 and 2 above
and, using the mouse, confirm that the plates in both capacitors are held at the same
values of potential: V = 1 for the upper plate and V = -1 for the lower plate. Capacitor 1 (a) For Capacitor 1 notice that the charge on each plate is given. (In this assignment, we will assume this charge is the maximum charge that can be stored on the plates.) Explain why it is highly unlikely that the value shown is expressed in Coulombs. (b) Using the mouse, display the electric field strength at the very center of the capacitor (between the two plates). Assume that this field strength is measured in 104 V/m (for example, a displayed value of 1.70 would really mean 1.70 X 104 V/m). Also, assume that the charge is measured in 10-12 C. Using this information, calculate the area of the plates. (c) You will notice that the electric field strength is greatly diminished outside the capacitor. What would happen to the strength of the field in this region if the plates are made larger? What if the area of the plates was made infinitely large? (d) Using the mouse, find the distance of separation of the plates. Then using this information calculate the capacitance of Capacitor 1. Capacitor 2
(a) Since the area of the plates of Capacitor 2 are the same as Capacitor 1, which capacitor will have the largest capacitance? Why? (b) Given that the plates of Capacitor 2 are held at the same potential difference as Capacitor 1, explain why the plates of Capacitor 2 hold less maximum charge than Capacitor 1. (c) Assuming again that the area of the plates between Capacitor 1 and 2 are the same, calculate the electric field strength between the plates of Capacitor 2. Does the applet agree? If not, calculate the percentage error between your results and the applet display. 3. The equation we use for capacitance of a flat-plate capacitor is C = eo A/d. Explain why this equation is not expected to produce the exact result for either capacitor. Which capacitor is this equation likely to produce the most accurate result, and why? |
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