A potential difference of 90 mV exists between the inner and outer surfaces of a

Question

A potential difference of 90 mV exists between the inner and outer surfaces of a cell membrane. The inner surface is negative relative to the outer surface. How much work is required to eject a positive sodium ion (Na^+) from the interior of the cell? A +4.00 mu C charge is located at the origin. Determine the electric potential at a distance of 2.00 m from the charge the electric potential energy of a -2.00 mu C charge located at (0, 2.00) m. A parallel-plate capacitor with area 0.200 m^2 and plate separation of3.00 mm is connected to a 600- V battery. What is the capacitance? How much the electric field between the plates? What is the electric field between the plates? Find the magnitude of the charge density on each plate without disconnecting the battery, the plates are moved farther apart. Qualitatively, what happens to each of the previous answers? Two capacitors are connected in parallel across a 12.0-V battery. If their capacitances are 12.0 mu F and 25.0 mu F, determine the voltage across each capacitor, the charge stored on each plate of each capacitor and the equivalent capacitance of the system. Repeat problem number 3 if the capacitors are connected in series.

Explanation / Answer

work = potential difference *charge

W = V*q = 90*10^-3*1.6*10^-19

W = 1.44*10^-20 J

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2)

(a)

electric potential V = k*q/r

V = 9*10^9*4*10^-6/2 = 18000 v

(b)

potential energy U = k*q1*q2/r

U = -9*10^9*4*10^-6*2*10^-6/2 = -0.036 J

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3

(a)

capacitance C = e0*A/d

A = area of cross section

d = seperation

C = 8.85*10^-12*0.2/(3*10^-3)

C = 5.9*10^-10 F

(b)

Q = C*V = 5.9*10^-10*6 = 3.54*10^-9 C

(c)

E = V/d = 6/(3*10^-3) = 2000 N/C

(d)

charge density = Q/A = 3.54*10^-9/0.2 = 1.7*10^-8 C/m^2

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4)

(a)

V1 = V2 = 12 v

(b)

Q1 = C1*V1 = 12*12 = 144 uC

Q2 = C2*V2 = 25*12 = 300 uC

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(c)

CP = C1 + C2 = 12 + 25 = 3 uF

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(5)

IN series charge is same

V1 = Q1/C1 = (C1*C2)*V/(C1+C2)*C1 = C2*V/(C1+C2)

V1 = 25*12/(12+25) = 8 v

V2 = V - V1 = 12 - 8 = 4 v

Q1 = C1*V1 = 12*8 = 100 uC

Q2 = C2*V2 = 4*25 = 100 uC

Cs = C1*C2/(C1+C2) = (12*25)/(12+25) = 8 uF

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