I have two questions: 1. Suppose that the resistance between the walls of a biol

Question

I have two questions:

1. Suppose that the resistance between the walls of a biological cell is 6.6 × 109 . (a) What is the current when the potential difference between the walls is 69 mV? (b) If the current is composed of Na+ ions (q = +e), how many such ions flow in 0.83 s?

2.

Two capacitors are connected to a battery. The battery voltage is V = 50 V, and the capacitances are C1 = 2.00 F and C2 = 4.00 F. Determine the total energy stored by the two capacitors when they are wired (a) in parallel and (b) in series.

Explanation / Answer

Part 1 )

I = V/R

I = 69 x 10^-3 / 6.6 x 10^9

I = 1.045 x 10^-11 A = 10.45 pA

part b )

q = It

q = 10.45 x 10^-12 x 0.83 = 8.68 x 10^-12 C = 8.68 pC

Part 2 )

E = 1/2 * CV^2

part a )

when capacitor in parallel

C = C1+ C2

= 2 + 4 = 6 micro F

E = 1/2 * 6 x 10^-6 x 50 x 50

E = 7.5 x 10^-3 J

part b )

when capacitor in series

C = C1*C2 / C1 + C2

C = 2*4 / (2+4)

C = 1.33 micro F

E = 1/2 * 1.33 x 10^-6 x 50^2

E = 1.6625 x 10^-3 J

E = 1.6625 mJ

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