Warning: foreach() argument must be of type array|object, bool given in /var/www/html/web/app/themes/studypress-core-theme/template-parts/header/mobile-offcanvas.php on line 20

Three capacitors having capacitances of 8.4, 8.4, and 4.2 \(\mu\)F are connected in series across a 36-V potential difference. (a) What is the charge on the 4.2-\(\mu\)F capacitor? (b) What is the total energy stored in all three capacitors? (c) 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? (d) What is the total energy now stored in the capacitors?

Short Answer

Expert verified
(a) 75.6 µC, (b) 1.36 mJ, (c) 3.6 V, (d) 0.136 mJ.

Step by step solution

01

Understanding Capacitors in Series

In a series connection, the charge \( Q \) on each capacitor is the same, and the total voltage \( V_{total} \) is the sum of voltages across each capacitor. The equivalent capacitance \( C_{eq} \) for capacitors in series is given by: \[ \frac{1}{C_{eq}} = \frac{1}{C_1} + \frac{1}{C_2} + \frac{1}{C_3} \]For our capacitors: \[ \frac{1}{C_{eq}} = \frac{1}{8.4} + \frac{1}{8.4} + \frac{1}{4.2} \]"Calculating” and solving, we find \( C_{eq} = 2.1 \, \mu\text{F} \)
02

Calculating Charge on the 4.2 µF Capacitor

For capacitors in series, the charge \( Q \) is same and calculated from \( Q = C_{eq} \times V_{total} \). Substituting the values, we get:\[ Q = 2.1 \, \mu\text{F} \times 36 \, \text{V} = 75.6 \, \mu\text{C} \]Thus, the charge on the 4.2 µF capacitor is 75.6 µC.
03

Calculating Total Energy Stored in Capacitors in Series

The energy \( E \) stored in a capacitor is given by \( E = \frac{1}{2} C V^2 \). Using the equivalent capacitance and voltage:\[ E_{total} = \frac{1}{2} \times 2.1 \, \mu\text{F} \times (36 \, \text{V})^2 = 1.36 \, \text{mJ} \]This is the total energy stored when capacitors are in series.
04

Reconfiguring Capacitors in Parallel

When the capacitors are reconnected in parallel, each has the same charge as before: 75.6 µC. The total capacitance \( C_{total} \) in parallel is:\[ C_{total} = C_1 + C_2 + C_3 = 8.4 + 8.4 + 4.2 = 21 \, \mu\text{F} \]Voltage across each capacitor in parallel is given by: \[ V = \frac{Q_{total}}{C_{total}} = \frac{75.6 \, \mu\text{C}}{21 \, \mu\text{F}} = 3.6 \, \text{V} \]
05

Calculating Total Energy Stored after Reconfiguration

The new total energy stored in the parallel configuration is:\[ E = \frac{1}{2} C_{total} V^2 = \frac{1}{2} \times 21 \, \mu\text{F} \times (3.6 \, \text{V})^2 = 0.136 \, \text{mJ} \]Note that energy is conserved but redistributed among capacitors during reconfiguration.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with Vaia!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Capacitance
Capacitance is the ability of a system to store an electric charge. It is a crucial property of capacitors, which are devices that can store energy in the electric field between their plates. The capacitance of a capacitor is defined by the formula: \[ C = \frac{Q}{V} \]where:
  • \( C \) is the capacitance
  • \( Q \) is the charge stored
  • \( V \) is the voltage across the capacitor

In essence, capacitance tells us how much charge a capacitor can hold per unit of voltage applied. It is measured in farads (F), although practical capacitors often use smaller units like microfarads (\( \mu F \)), nanofarads (nF), or picofarads (pF). Having a higher capacitance means that the capacitor can store more charge.
Understanding capacitance is essential when working with circuits, as it dictates how capacitors will interact with each other and influence the overall behavior of the system.
Energy Stored in Capacitors
The energy stored in a capacitor arises from the electric field between its plates when they are charged. This stored energy can be used in various applications, such as in flash photography or in power supplies for electronic devices. The formula for calculating the energy \( E \) stored in a capacitor is:\[ E = \frac{1}{2} C V^2 \]where:
  • \( E \) is the energy in joules (J)
  • \( C \) is the capacitance in farads
  • \( V \) is the voltage across the capacitor in volts

In the given exercise, by connecting capacitors in different configurations, we observe changes in the total energy stored. Initially, when capacitors are in series, their energy is calculated using the combined equivalent capacitance and the total applied voltage. By rearranging them in parallel, while maintaining the same charge, the energy stored changes due to the variation in voltage across each capacitor.
This shift in energy is crucial for understanding how capacitors can be utilized efficiently in various circuit designs.
Capacitors in Parallel
When capacitors are connected in parallel, they are arranged such that each capacitor's positive terminal is connected to the positive terminal of the power source, and the negative terminals are also connected together. This configuration ensures that the voltage across each capacitor is identical, but their charges can differ. The total capacitance \( C_{total} \) of capacitors in parallel is a straightforward sum:\[ C_{total} = C_1 + C_2 + C_3 + ... \]This means the total capacitance is the sum of the individual capacitances.
In the exercise scenario, when the capacitors were reconfigured to be in parallel with the same initial charge, the new total capacitance greatly influenced the voltage across each capacitor. By summing the capacitance of individual capacitors, their collective ability to store charge increases.
This configuration is particularly useful in circuits where a higher total capacitance is beneficial, permitting a larger reserve of stored energy at the same applied voltage. Understanding how capacitors add up in parallel is essential for designing circuits that can handle variable energy demands.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

The plates of a parallel-plate capacitor are 3.28 mm apart, and each has an area of 9.82 cm\(^2\). Each plate carries a charge of magnitude 4.35 \(\times\) 10\(^{-8}\) C. The plates are in vacuum. What is (a) the capacitance; (b) the potential difference between the plates; (c) the magnitude of the electric field between the plates?

When a 360-nF air capacitor (11 nF = 10\(^{-9}\) F) is connected to a power supply, the energy stored in the capacitor is 1.85 \(\times\) 10\(^{-5}\) J. While the capacitor is kept connected to the power supply, a slab of dielectric is inserted that completely fills the space between the plates. This increases the stored energy by 2.32 \(\times\) 10\(^{-5}\) J. (a) What is the potential difference between the capacitor plates? (b) What is the dielectric constant of the slab?

Electric eels and electric fish generate large potential differences that are used to stun enemies and prey. These potentials are produced by cells that each can generate 0.10 V. We can plausibly model such cells as charged capacitors. (a) How should these cells be connected (in series or in parallel) to produce a total potential of more than 0.10 V? (b) Using the connection in part (a), how many cells must be connected together to produce the 500-V surge of the electric eel?

A parallel-plate air capacitor has a capacitance of 920 pF. The charge on each plate is 3.90 \(\mu\)C. (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?

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?

See all solutions

Recommended explanations on Physics Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free