24.33 A 12.5-uF capacitor is connected to a power supply that keeps a constant p

Question

24.33 A 12.5-uF capacitor is connected to a power supply that keeps a constant potential difference of 24.0 V across the plates. A piece of material having a dielectric constant of 3.75 is placed between the plates, completely filling the space between them. a) How much energy is stored in the capacitor before and after the dielectric is inserted? (b) By how much did the energy change during the insertion? Did it increase or decrease? 24.34 . A parallel-plate capacitor has capacitance Co = 8.00 pF when there is air between the plates. The separation between the plates is 1.50 mm. (a) What is the maximum magnitude of harge Q that can be placed on each plate if the electric field in the region between the plates is not to exceed 3.00 × 104 V/m? (b) A dielectric with K = 2.70 is inserted between the plates of the capacitor, completely filling the volume between the plates. Now what is the maximum magnitude of charge on each plate if the electric field between the plates is not to exceed 3.00 × 104 V/m?

Explanation / Answer

24.33 : (A) U before = C V^2 /2

= (12.5 x 10^-6) (24^2) / 2

= 3.6 x 10^-3 J

Uafter = 3.75 C V^2 /2

= 13.5 x 10^-3 J

(B) It increases.

delta(U) = 9.9 x 10^-3 J

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