Weve seen that a cell membrane works as a capacitor. Muscle and nerve cells have
ID: 2289139 • Letter: W
Question
Weve seen that a cell membrane works as a capacitor. Muscle and nerve cells have excess positive charges outside and negative charges inside that lead to a resting potential of -70 mV inside the cell.
A cell has a membrane with a thickness of 5.0 nm and a capacitance of 90 pF.
a) what is the magnitude of the positive charge on the outside of the cell membrane, to the nearest pC?
b) 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)
Charge
Q=CV= (70*10-3)(90*10-12)
Q=6.3 pC
b)
Electric field
E=V/d =(70*10-3)/(5*10-9)
E=1.4*107 V/m
Force
F=QE=6.3*10-12*1.4*107
F=8.82*107 pN