Electromagnetism - Capacitor



Two real capacitors of equal capacitance (CC2) are shown in the figure. Initially, while the switch S is open, one of the capacitors is uncharged and the other carries charge Q0. The energy stored in the charged capacitor is U0. Sometime after the switch is closed, the capacitors Cand C2 carry charges Qand Q2, respectively; the voltages across the capacitors are Vand V2; and the energies stored in the capacitors are Uand U2.Which of the following statements is INCORRECT?

A. Q0 = ½ (QQ2)
B. QQ2
C. VV2
D. UU2
E. U0 = UU2
(GR9677 #25)
Solution:

Initial charge: Q0
Charge is conserved and distribute evenly
Q0 = ½ (QQ2)
(A) CORRECT

C = Q/V
For parallel capacitor V VV2
Given CC→ QQ2
(B) and (C) CORRECT

= ½QV
V= Vand QQ2 
→ UU2
(D) CORRECT

= ½Q→ = 2U/V
From (A) Q0 = ½ (QQ2),
2U0/V= ½ (2U1/V+ 2U2/V2)
V0 VV2 → 2U0 U1 U2
(E) INCORRECT

Answer: E

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