Given the circuit show, which has reached electrostatic equilibrium, a) Find Ce,
ID: 3309138 • Letter: G
Question
Given the circuit show, which has reached electrostatic equilibrium,
a) Find Ce, the single capacitance equivalent to the circuit
b) Find the charge on one plate of each of the original capacitors
c) Find the change in potential (sign and magnitude) in going from point a to point b in original circuit.
Given answers: a)Ce=1.625micro f
b) q1=qe=29.2micro C , q3=20.2micro C, qs=q2=q4=9.0micro C
c)Vab =V3=-3.4V
Explanation / Answer
Given,
r = 20 cm ; sigma = 1.5 pC/m^2
a)4 and 8 are in series
C48 = 4 x 8/(4 + 8) = 2.67 uF
Now, C48 in parallel with 6
C6-48 = 2.67 + 6 = 8.67 uF
Now, C6-48 is in series with 2
Ceq = 8.67 x 2/(8.67 + 2) = 1.63 uF
Hence, Ceq = 1.63 uF
b)Charge in the circuit is:
Q = CV = 1.63 x 10^-6 x 18 = 29.3 uC
Q1 = 29.3 uC
drop across C1 is V1 = 29.34/2 = 14.67 V
drop across parallel combination is:
Vp = 18 - 14.67 = 3.33 V
Q3 = C3V3 = 6 x 3.33 = 19.98 = 20 uC
Q2 = Q4
Q2 = Q4 = 29.2 - 20 = 9 uC
Hence, C1 = 29.34 uC ; C2 = 8.88 uC ; C3 = 20 uC ; C4 = 9 uC
c)Va - Vb = -3.33 V
(calculated in the former part)
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