A parallel plate capacitor is made with two square plates of side length 8cm sep

Question

A parallel plate capacitor is made with two square plates of side length 8cm separated by a 1.5mm air gap. a) What is the capacitance of this capacitor? b) If a positive charge of 420µC is placed on one side of the capacitor and a negative charge of 420µC is placed on the other, what is the potential difference between the two plates? Now, consider two different possibilities: c) While the two sides of the capacitor remain isolated (charge is conserved), a dielectric with k = 22.8 is inserted between the two plates. What are the new values of Q, C, and V ? d) The two plates are connected to a battery (constant potential source), a dielectric with k = 22.8 is inserted between the two plates. What are the new values of Q, C, and V ?

Explanation / Answer

a) Co = e0*A/d = (8.85*10^-12*0.08*0.08)/1.5*10^-3 = 3.776*10^-11 F

b) Vo = Qo/Co = 420*10^-6/3.776*10^-11 = 1.11*10^7 V

c) Q = kQo = 22.8*420*10^-6 = 0.009576 C

    C = kCo = 22.8* 3.776*10^-11 = 8.61*10^-10 F

    V = Q/C = 1.11*10^7 V

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