Part A We can model the cell as a capacitor, as we have seen. What is the magnit

Question

Part A We can model the cell as a capacitor, as we have seen. What is the magnitude of the charge on each "plate" when the membrane is at its resting potential of -70 mV? Express your answer using two significant figures. Answer must be in C. Part B How many sodium ions does this charge correspond to? Express your answer using two significant figures. Answer must be in sodium ions. Part A We can model the cell as a capacitor, as we have seen. What is the magnitude of the charge on each "plate" when the membrane is at its resting potential of -70 mV? Express your answer using two significant figures. Answer must be in C. Part B How many sodium ions does this charge correspond to? Express your answer using two significant figures. Answer must be in sodium ions. Part B How many sodium ions does this charge correspond to? Express your answer using two significant figures. Answer must be in sodium ions.

Explanation / Answer

In any event, it'll be +Q on one plate and -Q on the other.

C = ?0*A/d is good assuming the dielectric between the plates is a vacuum. I don't know enough about cell membranes to know how realistic this is. Do your notes not give a value for "membrane dielectric constant" (k) also known as "relative permittivity" (?r) ?

C = ?0*?r *A/d

With that you should find C = k?0*A/d where k = 9.0. From that you should get around 4.8*10^(-20) F. Use Q=C*deltaV with this to get about 4.8*10^(-12) C as your total charge on each "plate".

As for the sodium ions, just divide the total charge (4.8*10^(-12) C) by the charge of a proton (1.6*10^(-19) C) to get a total of 3.0*10^(7) sodium ions. (N=Q/e)

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