a) What is the current through the resistor just BEFORE the switch is thrown? b)

Question

a) What is the current through the resistor just BEFORE the switch is thrown?

b) What is the current through the resistor just AFTER the switch is thrown?

c) What is the charge across the capacitor just BEFORE the switch is thrown?

d) What is the charge on the capacitor just AFTER the switch is thrown?

e) What is the charge on the capacitor at a time t=0.1 msec after the switch is thrown?

f) How long does it take for the charge to reach 50% of the maximum value?

g) If R was doubled, how would that affect the amount of time it takes to fully charge the capacitor?

8. Considering the same circuit, only with the switch thrown from b to a at time t 0 after having been in position b for a long time. DATA:= 12 V, C-10 mA R = 20

Explanation / Answer

(A) just before, I = 0

(B) just after,

I = V / R = 12/20 = 0.60 A

(C) I = 0

so Vc = I R = 0

Q = C Vc = 0

(D) Vb -IR - Vc = 0

Vc = 12 - 12 = 0

Q = C Vc = 0

(E) time costant, T = RC = 20 x 10 x 10^-3

T = 200 x 10^-3s = 200 ms

Q = (10 x 12 mC)[1 - e^(-0.1/200)] = 0.06 mC

(f) Q = Q0[1 - e^(-t/T)]

0.50 = 1 - e^(-t/T)

- t / T = ln(0.50)

t = 138.6 ms

(g)

(but to charge fully, it taken infinite time so technically there will be no change in time.)

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.