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# Electrostatics: Coulomb's law, polarization, capacitance.

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1. If you turn on a faucet so that a thin stream of water flows from it, you may demonstrate to yourself that a charged object (such as a plastic comb) brought near it will deflect the water. The force is always attractive. Explain why this happens, in terms of the polarization of water. Draw a diagram to illustrate.

2. Suppose you have an uncharged metal sphere insulated from the ground. You also have in your possession a plastic rod that is negatively charged. Describe how you could put a positive charge on the metal sphere.

3. A negative charge of 2.0 micro coulombs is held at a distance of 0.30 m from a negative charge of 1.2 micro coulombs. Find the electrical force on the second charge due to the first charge, giving magnitude and direction.

4. An electron starts from rest in a uniform field of 30 N/C. (A) Determine its speed after a time of 1.0 microsecond. (B) Use the work-kinetic energy principle to find how far it traveled during this time.

5. Describe in your own words what capacitance is. What are its units?

6. What is the resulting capacitance of a 4.0 micro farad capacitor and a 10.0 micro farad capacitor hooked up in parallel? What is it if they are hooked in series?