Answer: Last Answer: .057 A Not yet correct, tries 1/20 Hint: There are three un

Question

Answer:  Last Answer: .057 A
Not yet correct, tries 1/20

Hint: There are three unknown currents, therefore you need 3 equations. You will have to analyze at least two separate loops of the circuit and keep track of parts of the current using the junction rule.

17[H]) Suppose that you replace the second battery with an uncharged 16 F capacitor. How much current flows across resistor R2 when the capacitor is essentially fully charged?

Correct, computer gets: 0.27 A

Hint: Instead of a voltage gain from the second battery we will now have a voltage drop across the capacitor. You should still end up with equations similar to those you found earlier. Which of the currents is directly transferring charge to the capacitor? That current will be equal to the rate of change of the charge on the capacitor's positive plate.

18[VH]) How long does it take the capacitor to reach half of its full charge?

--need help on how to solve this one

Explanation / Answer

1. current through R2 = i = V1/(R1+R2)

i2 = 8/(10+20)

i2 = 0.267 Amps

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use the charging eqn q = qo (!- e^-t/RC)

Req = (10*20)/(10 + 20) + 60

Req = 66.67 ohms

Ceq = 16uF

e^-t/RC = q/qo = -0.5

-t/RC = ln (2) = 0.693

t = 0.693 * 66.67 * 16 e -6

t = 0.74 ms

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