1: A parallel plate capacitor is charged by being connected to a battery and is then disconnected from the battery. The separation between the plates is then doubled. How does the electric field change? The potential difference? The total energy? Explain your reasoning.

2: You are a pencil-necked geek, fresh out of electrical engineering school, ready to change the world! With decent grades and a good word from a friend of a friend, you land a prestigious job as a technical engineer at Bob's High Tech Circuit Design Emporium and Car Wash on the edge of Silicon Valley, south of San Francisco. After working for a week drying cars, you are finally given your first assignment. Bob asks you to design a little circuit destined to make a McDonald's happy meal toy light up when squeezed. He also tells you that "due to a clerical error" the company has a huge surplus of 1 and 5 microfarad capacitors. He leaves you with the kind words of support, "Use them in your design, or else!"

After some work, you decide there are two possible configurations of capacitors (shown below) that you could use in your circuit. Your circuit requires the configuration with the larger stored electrical energy. Which circuit should you choose? Explain your reasoning and show your work. Assume the potential difference across each configuration is V.

3: Hmmm. The net charge in a capacitor is zero. What does a capacitor store??

4: A constant potential difference of 24 V is maintained between the terminals of a 0.25 m F parallel-plate air capacitor. A) A sheet of mylar is inserted between the plates of the capacitor, completely filling the space between the plates. When this is done, how much additional charge flows onto the positive plate of the capacitor? B) What is the total induced charge on either face of the mylar sheet? C) What effect does the mylar sheet have on the electric field between the plates? How does this jive with the increase in the charge on the plates which should serve to increase the field between the plates?

5: Here’s one out of the blue … The source of a star’s energy is thermonuclear fusion taking place in the core of the star. Estimate the temperature at the center of a star when nuclear fusion reactions begin. (hints: Nuclear fusion happens when two protons collide with enough energy to fuse into one heavier nucleus. Assume this can happen if the protons approach to within a distance of 10^-15 meters of each other. Also recall that the average kinetic energy of a particle of mass m in a gas at absolute temperature T is (3/2)kT