capacitance w/ a dielectric

[Addallat]

---

Members don't see this ad.

Can someone please help me figure out where I'm going wrong

Q: The inner and outer surfaces of a cell membrane act as plates in a parallel-plate capacitor. Consider a 1 µm^2 section of an axon: The dielectric constant of the membrane is 8 and the membrane is 6 nm thick. If the voltate across the membrane is 70 mV, what is the approximate magnitude of charge that resides on each side of the 1 µm^2 section? (note permittivity of free space constant = 8.83 x 10^-12 C^2.N m^2)


My answer:

Part 1

Capacitance = dielectric constant x permittivity free space constant x area/distance

(8) * (9* 10^-12) * (10^-12m) / (6x10^-9) = (12 * 10^-15) Farads


Part 2

Q = V * C

(70*10^-3) * (12*10^-15) = 840 * 10 ^ -18 = 8.4 * 10^-16C

this is question 8-32 in the TPR book
the book states the answer is
1*10^-15 C


I can't see where I'm going wrong and how they got their answer

 

[Addallat]

.

 

[HotHamH2O]

I worked it without the dialectric constant and got the answer the book gave. So the book must be wrong?

 

[Addallat]

dang that was annoying thanks for clearing that up