Physics 1029A/B Lecture Notes - Lecture 7: Surface Charge, Charge Density, Relative Permittivity

• School: Western University
• Department: Physics
• Course: Physics 1029A/B
• Professor: Martin Zinke- Allmang

Document Summary

Physics lecture 20 nerve membrane, capacitance and surface charge density. Example - determine for a resting nerve, (a) the capacitance per unit area of membrane, and (b) the surface charge density on the membrane in c/m . Part a: we know: nerve membrane = 7, membrane thickness: b = 6 nm. V m: electric field in nerve membrane, we use: c = a 0/b. Part b: surface charge density from electric field in capacitor: o o o. V m: do such values mean anything, capacitance. Schwann"s cells i. e. , b 300 b. C is proportional to 1/b c decreases 300 fold. Q = c v q decreases 300 fold for same potential difference: charge density. First: convert to surface concentration of ions cions e. Next we determine the fraction of surface sites which carry an ion: Typical number of atoms per unit area in a solid or liquid surface atom.