The membrane that surrounds a certain type of living cell has a surface area of 4.50 10-9 m2 and a thickness of 1.08 10-8 m. Assume that the membrane behaves like a parallel plate capacitor and has a dielectric constant of 5.40. If the charge in part (a) is due to K+ ions (charge +e), how many such ions are present on the outer surface?

4 answers

I would need to know the "charge in part (a)" to answer that. You have not said what it is.
If you know the charge, you only have to divide by e to get the number of K+ ions
I know the voltage is 54.6*10^-6V but when I tried to determine the charge, I got it wrong
(a) The potential on the outer surface of the membrane is +54.6 mV greater than that on the inside surface. How much charge resides on the outer surface?
ε₀=8.85 •10⁻¹² F/m
ε=5.4
e =1.6•10⁻¹⁹ C
A=4.50•10⁻⁹ m²
d=1.08•10 ⁻⁸ m
U=54.6•10⁻³V

C=ε•ε₀•A/d
C=q/U
ε•ε₀•A/d =q/U
q= ε•ε₀vA•U/d

q=Ne
N=q/e