Question 25.39: In Fig. 25-45,C1 = 10.0 μF, C2= 20.0 μF, and C3= 25.0μF. If ......
In Fig. 25-45,C_1 = 10.0 μF, C_2= 20.0 μF, and C_3= 25.0 μF. If no capacitor can withstand a potential difference of more than 100 V without failure, what are (a) the magnitude of the maximum potential difference that can exist between points A and B and (b) the maximum energy that can be stored in the three-capacitor arrangement?
(a) They each store the same charge, so the maximum voltage is across the smallest capacitor. With 100 V across 10 μF, then the voltage across the 20 μF capacitor is 50 V and the voltage across the 25 μF capacitor is 40 V. Therefore, the voltage across the arrangement is 190 V.
(b) Using Eq. 25-21 or Eq. 25-22, we sum the energies on the capacitors and obtain U_{total} = 0.095 J.
U=\frac{q^2}{2 C} (potential energy). (25-21)
U=\frac{1}{2} C V^2 (potential energy). (25-22)