Physics 2

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Practice Problems: Conductors in Electrostatic Equilibrium

1. (easy) A spherical hunk of solid metal (R = 0.1 m) is charged with trillions and trillions of excess electrons. Electrostatic equilibrium is established so that the E-field associated with the object has a magnitude of 400 v/m at its surface. A small test charge is then imagined to pop into existence inside the metal. The test charge happens to move from the center of the metal sphere to the surface. a. Where does the excess charge reside? b. Determine the work done by the E-field during this motion.

2. (moderate) If the object mentioned in question #1 was shaped like a submarine, make a sketch that includes the E-field at the surface in various locations. Be sure to include relative magnitude information by making the E-field vectors have appropriate lengths. Explain the details of the sketch.

3. (moderate) Explain why it is safer inside a car during a storm rather than in an open field. Explain the theory that supports your answer.

4. (moderate) Make a graph that shows electric potential as a function of distance from the center of a charged solid metal sphere (excess q = 3.7x10-9 C and R = 0.05 m). Calculate maximum potential for this system and record that value on the graph. Also, calculate the electric potential difference between a point found at R/2 and a point found at 2R from the center.

5. (easy) View the video below. Explain why the discharge from the Tesla Coil hits the tip of the grounding rod.