2012年AP电磁学简答题真题+答案+PDF下载
E&M. 1.
Two thin, concentric, conducting spherical shells, insulated from each other, have radii of 0.10 m and 0.20 m, as shown above. The inner shell is set at an electric potential of -100 V , and the outer shell is set at an electric potential of +100 V, with each potential defined relative to the conventional reference point. Let Qi and Qo represent the net charge on the inner and outer shells, respectively, and let r be the radial distance from the center of the shells. Express all algebraic answers in terms of Qi , Qo , r, and fundamental constants, as appropriate.
(a) Using Gauss’s Law, derive an algebraic expression for the electric field E(r) for 0.10 m < r < 0.20 m .
(b) Determine an algebraic expression for the electric field E(r) for r > 0.20 m .
(c) Determine an algebraic expression for the electric potential V(r) for r > 0.20 m .
(d) Using the numerical information given, calculate the value of the total charge QT on the two spherical shells (QT = Qi + Qo )
(e) On the axes below, sketch the electric field E as a function of r . Let the positive direction be radially outward.
(f) On the axes below, sketch the electric potential V as a function of r .
E&M. 2.
A physics student wishes to measure the resistivity of slightly conductive paper that has a thickness of 1.0 * 10-4 m . The student cuts a sheet of the conductive paper into strips of width 0.02 m and varying lengths, making five resistors labeled R1 to R5. Using an ohmmeter, the student measures the resistance of each strip, as shown above. The data are recorded below.
(a) Use the grid below to plot a linear graph of the data points from which the resistivity of the paper can be determined.Include labels and scales for both axes. Draw the straight line that best represents the data.
(b) Using the graph, calculate the resistivity of the paper.
The student uses resistors R4 and R5 to build a circuit using wire, a 1.5 V battery, an uncharged 10μF capacitor, and an open switch, as shown above.
(c) Calculate the time constant of the circuit.
(d) At time t = 0, the student closes the switch. On the axes below, sketch the magnitude of the voltage Vc across the capacitor and the magnitudes of the voltages VR4 and VR5 across each resistor as functions of time t. Clearly label each curve according to the circuit element it represents. On the axes, explicitly label any intercepts, asymptotes, maxima, or minima with values or expressions, as appropriate.
2012年AP电磁学简答题真题余下省略！
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