8. A capacitor has circular plates of diameter 5cm and separation 0.2mm. The pla

Question

8. A capacitor has circular plates of diameter 5cm and separation 0.2mm. The plates are After the plates are disconnected, how much work is required to increase the separation between the plates to 0.3 mm? 9. A constant potential difference of 12 V is maintained between the terminals of 0.3 uE parallel- plate capacitor with a 2 mm gap between the plates. A sheet of Plexiglas (k=3.4) is inserted between the plates, completely filling the space between the plates. How much additional charge flows onto the positive plate of the capacitor as a result of the dielectric? 10. A copper wire (density of free electrons 8.4*102 m3) has a diameter of 2.3mm and a length travel the length of the wire?

Explanation / Answer

8. C = e0 A / d

C = (8.854 x 10^-12)(pi 0.025^2) / 0.2 x 10^-3

C = 8.69 x 10^-11 F

Q = C V = 7.823 x 10^-10 C

Q will remain same.

Ui = Q^2 / 2 C = 3.52 x 10^-9 J

finally, C' = 2C/3

Uf = 3 Ui / 2 = 5.282 x 10^-9 J

Work required = Uf - Ui = 1.76 x 10^-9 J ......Ans

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