We\'ve seen that a cell membrane works as a capacitor. Muscle and nave cells hav

Question

We've seen that a cell membrane works as a capacitor. Muscle and nave cells have excess positive charges outside and negative charges inside that lead to a resting potential of -70 mV inside the cell. A all has a membrane with a thickness of 5.0 nm and a capacitance of 90 pF. What is the magnitude of the positive charge on the outside of the cell membrane, to the nearest pC The sodium ions that help give rise to this potential are singly ionized Na. What is the magnitude of the force on such an ion in the cell membrane, to the nearest pN

Explanation / Answer

a)

Magnitude of positive charge is

Q=CV =(90p)*(70*10-3)

Q=6.3 pC

b)

Electric field

E=V/d =70*10-3/(5*10-9) =1.4*107 V/m

Force of ion in cell membrane is

F=qE =(1.602*10-19)*1.4*107

F=2.24 pN

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