p240_ct9_w12_feb_2

# p240_ct9_w12_feb_2 - Physics 240 Winter 2012 Lecture#9 My...

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Physics 240 Winter 2012 Lecture #9 Dr. Dave Winn 2405 Randall Lab My Office Hours (1416 Randall Lab) Monday 1pm-3pm Tuesday 1pm-3pm Thursday 2pm-4pm (Prof. Gidley) Learning Assistant Office Hours Tuesday 4-8pm Thursday 4-6pm Also in chat room Tue/Thu evening!

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You slide a slab of dielectric between the plates of a parallel-plate capacitor. As you do this, the charges on the plates remain constant. What effect does adding the dielectric have on the potential difference between the capacitor plates? A. The potential difference increases. B. The potential difference remains the same. C. The potential difference decreases. D. not enough information given to decide Q24.8
You slide a slab of dielectric between the plates of a parallel-plate capacitor. As you do this, the potential difference between the plates remains constant. What effect does adding the dielectric have on the amount of charge on each of the capacitor plates? A. The amount of charge increases. B. The amount of charge remains the same. C. The amount of charge decreases. D. not enough information given to decide Q24.10

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Capacitors • Arrangements of conductors which store charge and energy • Capacitance measures efficiency of charge storage: C = Q/V • Determined by geometry of device; typically some size scale times 0 • To increase C, make storage area large, keep positive and negative charge close. . • Combining capacitors in parallel simply adds more capacitance: C eq = C i • Combining capacitors in series reduces the 1/C eq = 1/C i
Limits for capacitors in series Interesting limits for two capacitors in series: • When C 1 = C 2 = C, then C eq = C/2, the capacitance is cut in half • When C 1 >> C 2 , then C eq C 2 ; the equivalent capacitance is the smaller capacitor 2 1 2 1 C C C C C eq 2 1 1 2 1 2 2 1 1 1 1 C C C C C C C C C

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More complex arrangements • To understand a more complex arrangement,
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p240_ct9_w12_feb_2 - Physics 240 Winter 2012 Lecture#9 My...

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