4. The energy, W, stored in a capacitor is below. W (C, &) = 2 C a. Find the rate of energy variation as a capacitor varies with charge. b. Find the rate of energy variation as a capacitor varies with potential change, keeping capacitance constant.

(a) An 8.00/F capacitor is connected in parallel to another capacitor, producing a total capacitance of 5.00/F . What is the capacitance of the second capacitor? (b) What is unreasonable about this result? (c) Which assumptions are unreasonable or inconsistent?

(a) Why is it dangerous to touch the terminals of a high-voltage capacitor even after the voltage source that charged the capacitor is disconnected from the capacitor? (b) What can be done to make the capacitor safe to handle after the voltage source has been removed?

Consider the combination of capacitors in Figure P16.42. (a) Find the equivalent single capacitance of the two capacitors in series and redraw the diagram (called diagram 1) with this equivalent capacitance. (b) In diagram 1, find the equivalent capacitance of the three capacitors in parallel and redraw the diagram as a single battery and single capacitor in a loop. (c) Compute the charge on the single equivalent capacitor. (d) Returning to diagram 1, compute the charge on each individual capacitor. Does the sum agree with the value found in part (c)? (e) What is the charge on the 24.0-F capacitor and on the 8.00-F capacitor? Compute the voltage drop across (f) the 24.0-F capacitor and (g) the 8.00-F capacitor. Figure P16.42

Three capacitors are connected to a battery as shown in Figure P20.50. Their capacitances are C1 = 3C, C2 = C, and C3 = 5C. (a) What is the equivalent capacitance of this set of capacitors? (b) State the ranking of the capacitors according to the charge they store from largest to smallest. (c) Rank the capacitors according to the potential differences across them from largest to smallest. (d) What If? Assume C3 is increased. Explain what happens to the charge stored by each capacitor. Figure P20.50

Three capacitors having capacitances 8.4, 8.4, and 4.2 F are connected in series across a 36.0-V potential difference, (a) What is the total energy stored in all three capacitors? (b) The capacitors are disconnected from the potential difference without allowing them to discharge. They are then reconnected in parallel with each other with the positively charged plates connected together. What is the total energy now stored in the capacitors?

Unreasonable Results (a) An 8.00 F capacitor is connected in parallel to another capacitor, producing a total capacitance of 5.00 F. What is the capacitance of the second capacitor? (b) What is unreasonable about this result? (C) Which assumptions are unreasonable or inconsistent?

A parallel-plate capacitor has capacitance 3.00 F. (a) How much energy is stored in the capacitor if it is connected to a 6.00-V battery? (b) If the battery is disconnected and the distance between the charged plates doubled, what is the energy stored? (c) The battery is subsequently reattached to the capacitor, but the plate separation remains as in part (b). How much energy is stored? (Answer each part in microjoules.)

Three capacitors having capacitances of 8.40, 8.40, and 4.20F , respectively, are connected in series across a 36.0-V potential difference. (a) What is the charge on the 4.20F capacitor? (b) The capacitors are disconnected from the potential difference without allowing them to discharge. They are then reconnected in parallel with each other with the positively charged plates connected together. What is the voltage across each capacitor in the parallel combination?

Figure CQ16.3 shows equipotential contours in the region of space surrounding two charged conductors. Find (a) the work WAB in electron volts done by the electric force on a proton that moves from point A to point B. Similarly, find (b) WAC, (c) WAD, and (d) WAE. Figure CQ16.3