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Ch 24: Capacitance and Dielectrics
Young & Freedman Calc - University Physics 15th Edition
Young & Freedman Calc15th EditionUniversity PhysicsISBN: 9780135159552당신이 사용하는 게 아니라요?교과서 변경
24장, 문제 27

You have two identical capacitors and an external potential source.
(a) Compare the total energy stored in the capacitors when they are connected to the applied potential in series and in parallel.
(b) Compare the maximum amount of charge stored in each case.
(c) Energy storage in a capacitor can be limited by the maximum electric field between the plates. What is the ratio of the electric field for the series and parallel combinations?

검증된 단계별 안내
1
To compare the total energy stored in the capacitors when connected in series and parallel, start by recalling the formula for the energy stored in a capacitor: \( U = \frac{1}{2} C V^2 \). For capacitors in series, the equivalent capacitance \( C_s \) is given by \( \frac{1}{C_s} = \frac{1}{C_1} + \frac{1}{C_2} \). For identical capacitors, this simplifies to \( C_s = \frac{C}{2} \). For parallel, the equivalent capacitance \( C_p = C_1 + C_2 = 2C \). Substitute these into the energy formula to compare the energies.
To compare the maximum charge stored, use the relationship \( Q = CV \). For series, the charge on each capacitor is the same and equal to the charge on the equivalent capacitor \( Q_s = C_s V \). For parallel, the charge on each capacitor is \( Q_p = CV \). Calculate \( Q_s \) and \( Q_p \) using the equivalent capacitances from step 1.
To find the ratio of the electric field for the series and parallel combinations, recall that the electric field \( E \) in a capacitor is given by \( E = \frac{V}{d} \), where \( d \) is the separation between the plates. For series, the voltage across each capacitor is \( V/2 \), so \( E_s = \frac{V/2}{d} \). For parallel, the voltage across each capacitor is \( V \), so \( E_p = \frac{V}{d} \). Calculate the ratio \( \frac{E_s}{E_p} \).
Summarize the findings: For energy, compare \( U_s = \frac{1}{2} \frac{C}{2} V^2 \) with \( U_p = \frac{1}{2} 2C V^2 \). For charge, compare \( Q_s = \frac{C}{2} V \) with \( Q_p = CV \). For electric field, compare \( E_s = \frac{V}{2d} \) with \( E_p = \frac{V}{d} \).
Conclude by discussing the implications of these comparisons: In series, the energy and charge are lower, but the electric field is also lower, which might be beneficial in preventing dielectric breakdown. In parallel, the energy and charge are higher, but so is the electric field, which could be a limiting factor.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Capacitors in Series and Parallel

When capacitors are connected in series, the total capacitance decreases, calculated as the reciprocal of the sum of reciprocals of individual capacitances. In parallel, the total capacitance is the sum of individual capacitances. This affects both the energy stored and the charge distribution across the capacitors.
추천 영상:
가이드 코스
09:51
Combining Capacitors in Series & Parallel

Energy Stored in a Capacitor

The energy stored in a capacitor is given by the formula U = 0.5 * C * V^2, where C is the capacitance and V is the voltage across the capacitor. This formula helps compare the energy stored in series versus parallel configurations, as the effective capacitance and voltage differ in each setup.
추천 영상:
가이드 코스
09:26
Energy Stored by Capacitor

Electric Field in a Capacitor

The electric field (E) between the plates of a capacitor is determined by the voltage (V) and the separation distance (d) as E = V/d. In series and parallel configurations, the voltage across each capacitor changes, affecting the electric field. Understanding this helps compare the electric field strengths in different configurations.
추천 영상:
가이드 코스
06:13
Intro to Capacitors
관련 실천
교과서 질문

A parallel-plate capacitor has capacitance C0=8.00C_0=8.00 pF when there is air between the plates. The separation between the plates is 1.501.50 mm.

(a) What is the maximum magnitude of charge QQ that can be placed on each plate if the electric field in the region between the plates is not to exceed 3.00×1043.00\(\times\)10^4 V/m?

(b) A dielectric with K=2.70K = 2.70 is inserted between the plates of the capacitor, completely filling the volume between the plates. Now what is the maximum magnitude of charge on each plate if the electric field between the plates is not to exceed 3.00×1043.00\(\times\)10^4 V/m?

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교과서 질문

A constant potential difference of 1212 V is maintained between the terminals of a 0.250.25-μ\(\mu\)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 (see Table 24.124.1)?

(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? Explain how you can reconcile this with the increase in charge on the plates, which acts to increase the electric field.

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교과서 질문

A 5.805.80-μ\(\mu\)F, parallel-plate, air capacitor has a plate separation of 5.005.00 mm and is charged to a potential difference of 400400 V. Calculate the energy density in the region between the plates, in units of J/m3.

2037
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교과서 질문

A parallel-plate air capacitor has a capacitance of 920 pF. The charge on each plate is 3.90 uC. (a) What is the potential difference between the plates? (b) If the charge is kept constant, what will be the potential difference if the plate separation is doubled? (c) How much work is required to double the separation?

2994
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교과서 질문

Polystyrene has dielectric constant 2.62.6 and dielectric strength 2.0×1072.0\(\times\)10^7 V/m. A piece of polystyrene is used as a dielectric in a parallel-plate capacitor, filling the volume between the plates.

(a) When the electric field between the plates is 8080%% of the dielectric strength, what is the energy density of the stored?

(b) When the capacitor is connected to a battery with voltage 500.0500.0 V, the electric field between the plates is 80%80\% of the dielectric strength. What is the area of each plate if the capacitor stores 0.2000.200 mJ of energy under these conditions?

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교과서 질문

An air capacitor is made from two flat parallel plates 1.501.50 mm apart. The magnitude of charge on each plate is 0.01800.0180 μ\(\mu\)C when the potential difference is 200200 V.

(a) What is the capacitance?

(b) What is the area of each plate?

(c) What maximum voltage can be applied without dielectric breakdown? (Dielectric breakdown for air occurs at an electric-field strength of 3.0×1063.0\(\times\)10^6 V/m.)

(d) When the charge is 0.01800.0180 μ\(\mu\)C, what total energy is stored?

1447
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