Halliday/Resnick/Walker Fundamentals of Physics Classroom Response System Questions Chapter 25 Capacitance Interactive Lecture Questions

25.2.1. How much charge is on the plates of a 11-µF capacitor that has been connected to a 120 V dc power supply for a long time? a) 1.3 × 103 C b) 9.2 × 102 C c) 1.1 × 104 C d) 1.3 × 106 C e) 1.2 × 101 C

25.2.1. How much charge is on the plates of a 11-µF capacitor that has been connected to a 120 V dc power supply for a long time? a) 1.3 × 103 C b) 9.2 × 102 C c) 1.1 × 104 C d) 1.3 × 106 C e) 1.2 × 101 C

25. 2. 2. A 150-µF capacitor is fully-charged when it has 6 25.2.2. A 150-µF capacitor is fully-charged when it has 6.1 × 103 C on its plates. What is the potential difference across the plates of the capacitor? a) 250 V b) 41 V c) 0.0024 V d) 2.5 V e) 4.1 V

25. 2. 2. A 150-µF capacitor is fully-charged when it has 6 25.2.2. A 150-µF capacitor is fully-charged when it has 6.1 × 103 C on its plates. What is the potential difference across the plates of the capacitor? a) 250 V b) 41 V c) 0.0024 V d) 2.5 V e) 4.1 V

25.3.1. What is the minimum requirement for a capacitor? a) two conducting surfaces b) two closely-spaced plates c) two closely-spaced surfaces d) a single conductor

25.3.1. What is the minimum requirement for a capacitor? a) two conducting surfaces b) two closely-spaced plates c) two closely-spaced surfaces d) a single conductor

25.3.2. In calculating both the electric field and the capacitance of two closely spaced conducting plates, it is frequently assumed that the area of the plates is somewhat larger than the distance between the plates. Why is this assumption made? a) The capacitance is too small to calculate if the plates are too far apart. b) The electric field near the edges of the plates is not uniform. c) The charge would otherwise be too small to generate a significant electric field. d) Coulomb’s law would not otherwise apply. e) Gauss’ law would not otherwise apply.

25.3.2. In calculating both the electric field and the capacitance of two closely spaced conducting plates, it is frequently assumed that the area of the plates is somewhat larger than the distance between the plates. Why is this assumption made? a) The capacitance is too small to calculate if the plates are too far apart. b) The electric field near the edges of the plates is not uniform. c) The charge would otherwise be too small to generate a significant electric field. d) Coulomb’s law would not otherwise apply. e) Gauss’ law would not otherwise apply.

25.3.3. An electrical outlet has two vertical slots and a hole into which a three prong plug may be inserted. The maximum potential difference between the two vertical slots is 120 volts. The hole is connected to earth ground. Estimate the maximum electric field that exists between the two vertical slots. a) 240 V/m b) 4800 V/m c) 9200 V/m d) 120 V/m e) 6300 V/m

25.3.3. An electrical outlet has two vertical slots and a hole into which a three prong plug may be inserted. The maximum potential difference between the two vertical slots is 120 volts. The hole is connected to earth ground. Estimate the maximum electric field that exists between the two vertical slots. a) 240 V/m b) 4800 V/m c) 9200 V/m d) 120 V/m e) 6300 V/m

25.3.4. The plates of an isolated parallel plate capacitor with a capacitance C carry a charge Q. What is the capacitance of the capacitor if the charge is increased to 4Q? a) C/2 b) C/4 c) 4C d) 2C e) C

25.3.4. The plates of an isolated parallel plate capacitor with a capacitance C carry a charge Q. What is the capacitance of the capacitor if the charge is increased to 4Q? a) C/2 b) C/4 c) 4C d) 2C e) C

25.3.5. A parallel plate capacitor with plates of area A and plate separation d is charged so that the potential difference between its plates is V. If the capacitor is then isolated and its plate separation is increased to 2d, what is the potential difference between the plates? a) 4V b) 2V c) V d) 0.5V e) 0.25V

25.3.5. A parallel plate capacitor with plates of area A and plate separation d is charged so that the potential difference between its plates is V. If the capacitor is then isolated and its plate separation is increased to 2d, what is the potential difference between the plates? a) 4V b) 2V c) V d) 0.5V e) 0.25V

25. 4. 1. Capacitor B has one-half the capacitance of capacitor A 25.4.1. Capacitor B has one-half the capacitance of capacitor A. How does the charge on capacitor A compare to that on B when the two are connected in series to a battery for a long time? a) The charge on capacitor A is one-fourth the charge on capacitor B. b) The charge on capacitor A is one-half the charge on capacitor B. c) The charge on capacitor A is the same as the charge on capacitor B. d) The charge on capacitor A is twice the charge on capacitor B. e) The charge on capacitor A is four times the charge on capacitor B.

25. 4. 1. Capacitor B has one-half the capacitance of capacitor A 25.4.1. Capacitor B has one-half the capacitance of capacitor A. How does the charge on capacitor A compare to that on B when the two are connected in series to a battery for a long time? a) The charge on capacitor A is one-fourth the charge on capacitor B. b) The charge on capacitor A is one-half the charge on capacitor B. c) The charge on capacitor A is the same as the charge on capacitor B. d) The charge on capacitor A is twice the charge on capacitor B. e) The charge on capacitor A is four times the charge on capacitor B.

25. 4. 2. Capacitor B has one-half the capacitance of capacitor A 25.4.2. Capacitor B has one-half the capacitance of capacitor A. How does the charge on capacitor A compare to that on B when the two are connected in parallel with a battery for a long time? a) The charge on capacitor A is one-fourth the charge on capacitor B. b) The charge on capacitor A is one-half the charge on capacitor B. c) The charge on capacitor A is the same as the charge on capacitor B. d) The charge on capacitor A is twice the charge on capacitor B. e) The charge on capacitor A is four times the charge on capacitor B.

25. 4. 2. Capacitor B has one-half the capacitance of capacitor A 25.4.2. Capacitor B has one-half the capacitance of capacitor A. How does the charge on capacitor A compare to that on B when the two are connected in parallel with a battery for a long time? a) The charge on capacitor A is one-fourth the charge on capacitor B. b) The charge on capacitor A is one-half the charge on capacitor B. c) The charge on capacitor A is the same as the charge on capacitor B. d) The charge on capacitor A is twice the charge on capacitor B. e) The charge on capacitor A is four times the charge on capacitor B.

25. 4. 3. Capacitor B has one-half the capacitance of capacitor A 25.4.3. Capacitor B has one-half the capacitance of capacitor A. How does the potential difference on capacitor A compare to that on B when the two are connected in series with a battery for a long time? a) The potential difference on capacitor A is one-fourth the charge on capacitor B. b) The potential difference on capacitor A is one-half the charge on capacitor B. c) The potential difference on capacitor A is the same as the charge on capacitor B. d) The potential difference on capacitor A is twice the charge on capacitor B. e) The potential difference on capacitor A is four times the charge on capacitor B.

25. 4. 3. Capacitor B has one-half the capacitance of capacitor A 25.4.3. Capacitor B has one-half the capacitance of capacitor A. How does the potential difference on capacitor A compare to that on B when the two are connected in series with a battery for a long time? a) The potential difference on capacitor A is one-fourth the charge on capacitor B. b) The potential difference on capacitor A is one-half the charge on capacitor B. c) The potential difference on capacitor A is the same as the charge on capacitor B. d) The potential difference on capacitor A is twice the charge on capacitor B. e) The potential difference on capacitor A is four times the charge on capacitor B.

25.4.4. Two parallel conducting plates are connected to a battery for a long time and become fully-charged. How does the potential difference across the plates change, if at all, when a conducting slab is inserted in between the plates without touching wither plate? a) The potential difference will increase. b) The potential difference will decrease. c) The potential difference will remain unchanged.

25.4.4. Two parallel conducting plates are connected to a battery for a long time and become fully-charged. How does the potential difference across the plates change, if at all, when a conducting slab is inserted in between the plates without touching wither plate? a) The potential difference will increase. b) The potential difference will decrease. c) The potential difference will remain unchanged.

25.4.5. Two parallel conducting plates are connected to a battery for a long time and become fully-charged. How does the charge on the plates change, if at all, when a conducting slab is inserted in between the plates without touching either plate? a) The charge will increase. b) The charge will decrease. c) The charge will remain unchanged.

25.4.5. Two parallel conducting plates are connected to a battery for a long time and become fully-charged. How does the charge on the plates change, if at all, when a conducting slab is inserted in between the plates without touching either plate? a) The charge will increase. b) The charge will decrease. c) The charge will remain unchanged.

25.4.6. Two parallel conducting plates are connected to a battery for a long time and become fully-charged. How does the capacitance change, if at all, when a conducting slab is inserted in between the plates without touching wither plate? a) The capacitance will increase. b) The capacitance will decrease. c) The capacitance will remain unchanged.

25.4.6. Two parallel conducting plates are connected to a battery for a long time and become fully-charged. How does the capacitance change, if at all, when a conducting slab is inserted in between the plates without touching wither plate? a) The capacitance will increase. b) The capacitance will decrease. c) The capacitance will remain unchanged.

25.4.7. Three parallel plate capacitors, each having a capacitance of 1.0 µF are connected in series. The potential difference across the combination is 100 V. What is the charge on any one of the capacitors? a) 33 C b) 330 C c) 3300 C d) 100 C e) 1000 C

25.4.7. Three parallel plate capacitors, each having a capacitance of 1.0 µF are connected in series. The potential difference across the combination is 100 V. What is the charge on any one of the capacitors? a) 33 C b) 330 C c) 3300 C d) 100 C e) 1000 C

25.5.1. The plates of an isolated parallel plate capacitor are separated by a distance d and carry charge of magnitude q. The distance between the plates is then reduced to d/2. How is the energy stored in the capacitor affected by this change? a) The energy increases to twice its initial value. b) The energy increases to four times its initial value. c) The energy is not affected by this change. d) The energy decreases to one fourth of its initial value. e) The energy decreases to one half of its initial value.

25.5.1. The plates of an isolated parallel plate capacitor are separated by a distance d and carry charge of magnitude q. The distance between the plates is then reduced to d/2. How is the energy stored in the capacitor affected by this change? a) The energy increases to twice its initial value. b) The energy increases to four times its initial value. c) The energy is not affected by this change. d) The energy decreases to one fourth of its initial value. e) The energy decreases to one half of its initial value.

25. 5. 2. A capacitor has a very large capacitance of 10 F 25.5.2. A capacitor has a very large capacitance of 10 F. The capacitor is charged by placing a potential difference of 2 V between its plates. How much energy is stored in the capacitor? a) 2000 J b) 500 J c) 100 J d) 40 J e) 20 J

25. 5. 2. A capacitor has a very large capacitance of 10 F 25.5.2. A capacitor has a very large capacitance of 10 F. The capacitor is charged by placing a potential difference of 2 V between its plates. How much energy is stored in the capacitor? a) 2000 J b) 500 J c) 100 J d) 40 J e) 20 J

25.6.1. The plates of an isolated parallel plate capacitor with a capacitance C carry a charge Q. The plate separation is d. Initially, the space between the plates contains only air. Then, a Teflon ( = 2.1) sheet of thickness 0.5d is inserted between, but not touching, the plates. How does the electric field between the plates change as a result of inserting the Teflon sheet? a) The electric field will decrease to approximately one-half its initial value. b) The electric field will not be affected. c) The electric field will increase to approximately twice its initial value. d) The electric field will be zero volts per meter.

25.6.1. The plates of an isolated parallel plate capacitor with a capacitance C carry a charge Q. The plate separation is d. Initially, the space between the plates contains only air. Then, a Teflon ( = 2.1) sheet of thickness 0.5d is inserted between, but not touching, the plates. How does the electric field between the plates change as a result of inserting the Teflon sheet? a) The electric field will decrease to approximately one-half its initial value. b) The electric field will not be affected. c) The electric field will increase to approximately twice its initial value. d) The electric field will be zero volts per meter.

25.6.2. A parallel plate capacitor is connected to a battery that maintains a constant potential difference across the plates. Initially, the space between the plates contains only air. Then, a Teflon ( = 2.1) sheet is inserted between, but not touching, the plates. How does the stored energy of the capacitor change as a result of inserting the Teflon sheet? a) The energy will decrease. b) The energy will not be affected. c) The energy will increase. d) The energy will be zero joules.

25.6.2. A parallel plate capacitor is connected to a battery that maintains a constant potential difference across the plates. Initially, the space between the plates contains only air. Then, a Teflon ( = 2.1) sheet is inserted between, but not touching, the plates. How does the stored energy of the capacitor change as a result of inserting the Teflon sheet? a) The energy will decrease. b) The energy will not be affected. c) The energy will increase. d) The energy will be zero joules.

25. 6. 3. A parallel plate capacitor is fully charged at a potential V 25.6.3. A parallel plate capacitor is fully charged at a potential V. A dielectric with constant  = 4 is inserted between the plates of the capacitor while the potential difference between the plates remains constant. Which one of the following statements is false concerning this situation? a) The energy density remains unchanged. b) The capacitance increases by a factor of four. c) The stored energy increases by a factor of four. d) The charge on the capacitor increases by a factor of four. e) The electric field between the plates increases by a factor of four.

25. 6. 3. A parallel plate capacitor is fully charged at a potential V 25.6.3. A parallel plate capacitor is fully charged at a potential V. A dielectric with constant  = 4 is inserted between the plates of the capacitor while the potential difference between the plates remains constant. Which one of the following statements is false concerning this situation? a) The energy density remains unchanged. b) The capacitance increases by a factor of four. c) The stored energy increases by a factor of four. d) The charge on the capacitor increases by a factor of four. e) The electric field between the plates increases by a factor of four.

25.6.4. Which one of the following changes will necessarily increase the capacitance of a capacitor? a) decreasing the charge on the plates b) increasing the charge on the plates c) placing a dielectric between the plates d) increasing the potential difference between the plates e) decreasing the potential difference between the plates

25.6.4. Which one of the following changes will necessarily increase the capacitance of a capacitor? a) decreasing the charge on the plates b) increasing the charge on the plates c) placing a dielectric between the plates d) increasing the potential difference between the plates e) decreasing the potential difference between the plates

25.6.5. Complete the following statement: When a dielectric with constant  is inserted between the plates of a charged isolated capacitor a) the capacitance is reduced by a factor . b) the charge on the plates is reduced by a factor of . c) the charge on the plates is increased by a factor of . d) the electric field between the plates is reduced by a factor of . e) the potential difference between the plates is increased by a factor of 

25.6.5. Complete the following statement: When a dielectric with constant  is inserted between the plates of a charged isolated capacitor a) the capacitance is reduced by a factor . b) the charge on the plates is reduced by a factor of . c) the charge on the plates is increased by a factor of . d) the electric field between the plates is reduced by a factor of . e) the potential difference between the plates is increased by a factor of 

25.6.6. The figure shows four parallel plate capacitors: A, B, C, and D. Each capacitor carries the same charge Q and has the same plate area A. As suggested by the figure, the plates of capacitors A and C are separated by a distance d while those of B and D are separated by a distance 2d. Capacitors A and B are maintained in vacuum while capacitors C and D contain dielectrics with constant  = 5. Which of the following choices ranks the capacitors in order of increasing capacitance? a) A, B, C, D b) B, A, C, D c) A, B, D, C d) B, A, D, C e) D, C, B, A

25.6.6. The figure shows four parallel plate capacitors: A, B, C, and D. Each capacitor carries the same charge Q and has the same plate area A. As suggested by the figure, the plates of capacitors A and C are separated by a distance d while those of B and D are separated by a distance 2d. Capacitors A and B are maintained in vacuum while capacitors C and D contain dielectrics with constant  = 5. Which of the following choices ranks the capacitors in order of increasing capacitance? a) A, B, C, D b) B, A, C, D c) A, B, D, C d) B, A, D, C e) D, C, B, A