Chapter 26: Q.15 (page 738)
The electric potential along the x-axis is , where is in meters. What is at (a)role="math" localid="1649581712352" and (b) role="math" localid="1649581719374" ?
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Chapter 26: Q.15 (page 738)
The electric potential along the x-axis is , where is in meters. What is at (a)role="math" localid="1649581712352" and (b) role="math" localid="1649581719374" ?
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A nerve cell in its resting state has a membrane potential of , meaning that the potential inside the cell is less than the potential outside due to a layer of negative charge on the inner surface of the cell wall and a layer of positive charge on the outer surface. This effectively makes the cell wall a charged capacitor. When the nerve cell fires, sodium ions,, flood through the cell wall to briefly switch the membrane potential to . Model the central body of a nerve cell-the soma-as a diameter sphere with a -thick cell wall whose dielectric constant is 9.0. Because a cell's diameter is much larger than the wall thickness, it is reasonable to ignore the curvature of the cell and think of it as a parallel-plate capacitor. How many sodium ions enter the cell as it fires?
A switch that connects a battery to a 10 mF capacitor is closed. Several seconds later you find that the capacitor plates are charged to 30 mC. What is the emf of the battery?
Estimate the electric fields and at points 1 and 2 in Figure Q26.4. Don’t forget that is a vector.

Consider a uniformly charged sphere of radius R and total cAlC charge Q. The electric field outside the sphere is simply that of a point charge Q. In Chapter 24, we used Gauss's law to find that the electric field inside the sphere is radially outward with field strength
a. The electric potential outside the sphere is that of a point charge Q. Find an expression for the electric potentialat position r inside the sphere. As a reference, let at the surface of the sphere.
b. What is the ratio
c. Graph V versus r for 0 r 3 R.
A -diameter parallel-plate capacitor with a spacing of is charged to . What are
(a) the total energy stored in the electric field and
(b) the energy density?
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