Three capacitors are connected to a battery as shown in the figure below. Their
ID: 2273120 • Letter: T
Question
Three capacitors are connected to a battery as shown in the figure below. Their capacitances are C1 = 3C, C2 = C, and C3 = 5C.
(a) What is the equivalent capacitance of this set of capacitors (in terms of C)?
(b) State the ranking of the capacitors according to the charge they store, from largest to smallest.
Q > Q > Q
(c) Rank the capacitors according to the potential differences across them, from largest to smallest.
(d) Assume C3 is increased. Explain what happens to the charge stored by each capacitor.
Q3, Q1, and Q2 increases. Q3 and Q2 increases; Q1 decreases. Q3 and Q1 increases; Q2 decreases. All charges stay the same.
Explanation / Answer
a)
C2 and C3 are in parallel
C23=C2+C3 =C+5C
C23=6C
C1 and C23 are in series
Ceq =C1*C23/(C1+C23)
Ceq =3C*6C/(3C+6C)
Ceq =2C
b)
total charge
Q=Ceq*V =2C*V
Q=2CV
Q1=Q=2CV
Q2=Q*(C2/C2+C3) =2CV*(C/C+5C)
Q2=0.33CV
Q3 =Q-Q2=1.67CV
Q1>Q3>Q2
c)
V1 =Q1/C1 =2CV/3C
V1=0.67V
V2=Q2/C2 =0.33CV/C
V2=0.33V
V3=Q3/C3 =3.33CV/5C
V3=0.33V
V1>V2=V3
d)
Q1 increases and Q2 and Q3 decrease
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