LTE VIVA session.masteringphysics.com Item 2 MasteringPhysics 2 of 7 Item 2 A pa
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Question
LTE VIVA session.masteringphysics.com Item 2 MasteringPhysics 2 of 7 Item 2 A parallel-plate capacitor has square plates that are 9.00 cm on each side and 4.10 mm apart. The space between the plates is completely filled with two square slabs of dielectric, each 9.00 cm on a side and 2.05 mm thick. One slab is pyrex glass and the other is polystyrene Part A If the potential difference between the plates is 78.0 V,how much electrical energy is stored in the capacit or? Express your answer with the appropriate units. v-1 Value Units Submit Give Up Continue >Explanation / Answer
Capacitance = k x 0 x area / separation
C = k * 8.854 10^-12 * (0.09)2 / 0.0041 = 17.49 pF ( k=1 air )
k coeff dielectric :
pyrex glass =5.1
polystyrene= 2.6
k moy = (5.1 +2.6 ) / 2 = 3.85
C = k * 9.3748235 = 3.85 * 17.49 = 67.33 pF
U= 1/2 C V^2 = 0.5 * 67.33* 10^-12 * 78^2 = 2.048 10-7 J
Energy stored in capacitor
Q = CV=67.33*10^-12 * 78 = 5.251 nC
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