Physics help?? i dont understand, i keep trying but its not giving me the right answers?

Question

A typical cell membrane is 8.0 nm thick and has an electrical resistivity of 1.3 107 ·m.

(a) If the potential difference between the inner and outer surfaces of a cell membrane is 75 mV, how much current flows through a square area of membrane 1.4 µm on a side?

__ A

(b) Suppose the thickness of the membrane is doubled, but the resistivity and potential difference remain the same. Does the current increase or decrease?

increases

remains the same

decreases

By what factor?

Answer 1

To the extent that the membrane obeys Ohm's law, you have

I = V/R = VA/(rho)L = 75 x 10^-3 x (1.4 x 10^-6)^2/(1.3 x 10^7 x 8.0 x 10^-9) = 1.41 x 10^-12 A

Doubling the thickness will halve the current.