Capacitors

Homework Assignment

Questions: 2, 4, 11, 14, 17

Problems: 5, 12, 13, 27, 29, 30, 38, 47, 92

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Q2. The plates of a capacitor are connected to a battery. What happens to the charge on the plates if the connecting wires are removed from the battery? What happens to the charge if the wires are removed from the battery and connected to each other?

Q4. A pair of capacitors are connected in parallel while an identical pair are connected in series. Which pair would be more dangerous to handle after being connected to the same voltage source?

Q11. If the potential difference across a capacitor is doubled, by what factor does the energy stored change?

Q14. An air-filled capacitor is charged, then disconnected from the power supply, and finally connected to a voltmeter. Explain how and why the voltage reading changes when a dielectric is inserted between the plates of the capacitor.

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Some useful prefixes:

m = milli- = 10 ^{- 3}

= micro- = 10 ^{- 6}

n = nano- = 10 ^{- 9}

p = pico- = 10 ^{- 12}

26.5. A parallel-plate capacitor has a capacitance of 19.0 microFarads (19.0 F = 19.0 x 10 ^{- 6} F) What charge on each plate produces a potential difference of 36.0 V between the plates?

26.12. The plates of a parallel-plate capacitor are separated by 0.20 mm. If the space betweenthe plates is air, what plate area is required to provide a capacitance of 9.0 pF (picoFarads = 10 ^{- 12} F)?

26.13. When a potential difference of 150 V is applied to the plates of a parallel-plate capacitor, the plates carry a surface charge density of 30 nC/cm² (nC = nanoCoulombs = 10 ^{- 9} C). What is the spacing between the plates?

26.27. (a) Two capacitors, C₁ = 2.0 microFarads = 2.0 F and C₂ = 16.0 microFarads = 16.0 F, are connected in parallel. What is the equivalent capacitance of the combination?

(b) Calculate the equivalent capacitance of the two capacitors if they are connected in series.

26.29. (a) Determine the equivalent capacitance for the capacitor network shown in Figure P26.29.

(b) If the network is connected to a 12-V battery, calculate the potential difference across each capacitor and the charge on each capacitor.

26.30. Eval;uate the equivalent capacitance of the configuration shown in Figure P26.30. All the capacitors are identical, each with a capacitance C.

26.38. Find the equivalent capacitance between points a and b for the group of capacitors connected as shown in Figure P26.38 if C₁ = 5.0 F and C₂ = 10.0 F and C₃ = 2.00 F.

26.47. The energy stored in a 12.0 F capacitor is 130 J. Determine the following:

(a) the charge on the capacitor and

(b) the potential difference across it.

26.92. Determine the effective capacitance of the combination shown in Figure P26.92. (Hint: Consider the symmetry involved!)

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(c) Doug Davis, 2002; all rights reserved