AP Physics C: Electricity & Magnetism 8.3 B Describe the Electric Field Generated By Charged Conductors or Insulators Questions

Describe electric fields generated by charged conductors or insulators and connect field behavior to the distribution of charge.

Exam points

apply zero interior field and surface charge conditions to a conductor in electrostatic equilibrium
treat the exterior field of a spherical conductor as that of a central point charge
distinguish conductor and insulator field behavior using charge distributions or radial graphs
predict how a conductor's surface charge redistributes near another charged object

[Maximum number: 1]

An isolated, air-filled, charged capacitor consists of two conducting, coaxial, cylindrical shells that each have length L. The inner shell has radius $R_{1}$ and the outer shell has radius $R_{2}$ , as shown in Figure 1, where $R_{1}<R_{2} \ll L$ . The surface charge densities (amounts of charge per unit area) of the inner and outer shells are $+\sigma_{1}$ and $-\sigma_{2}$ , respectively. The absolute values of the total charges on the shells are equal.

Figure 1

Note: Figures not drawn to scale.

On the axes shown in Figure 2, sketch a graph of E as a function of r from r=0 to a position that is outside the outer shell.

Figure 2

(iii) For sketching a graph that is zero for both $0<r<R_{1}$ and $r>R_{2}$

Point A6

For sketching a graph that is decreasing and concave up for $R_{1}<r<R_{2}$

Scoring Note: The curve does not have to intersect the vertical dashed lines for this

point to be earned.

Example Response

Figure 2

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AP Physics C: Electricity & Magnetism 8.3 B Describe the Electric Field Generated By Charged Conductors or Insulators Questions question 1