Physics for Scientists and Engineers 8ed - ch26 - PowerPoint Slides

# Physics for Scientists and Engineers 8ed - ch26 - PowerPoint Slides

This preview shows pages 1–12. Sign up to view the full content.

Chapter 26 Capacitance and Dielectrics

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Capacitors Capacitors are devices that store electric charge Examples of where capacitors are used include: radio receivers filters in power supplies to eliminate sparking in automobile ignition systems energy-storing devices in electronic flashes
Definition of Capacitance The capacitance , C , of a capacitor is defined as the ratio of the magnitude of the charge on either conductor to the potential difference between the conductors The SI unit of capacitance is the farad (F) Q C V

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Makeup of a Capacitor A capacitor consists of two conductors These conductors are called plates When the conductor is charged, the plates carry charges of equal magnitude and opposite directions A potential difference exists between the plates due to the charge
More About Capacitance Capacitance will always be a positive quantity The capacitance of a given capacitor is constant The capacitance is a measure of the capacitor’s ability to store charge The farad is a large unit, typically you will see microfarads ( μ F) and picofarads (pF)

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Parallel Plate Capacitor Each plate is connected to a terminal of the battery The battery is a source of potential difference If the capacitor is initially uncharged, the battery establishes an electric field in the connecting wires
Parallel Plate Capacitor, cont This field applies a force on electrons in the wire just outside of the plates The force causes the electrons to move onto the negative plate This continues until equilibrium is achieved The plate, the wire and the terminal are all at the same potential At this point, there is no field present in the wire and the movement of the electrons ceases

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Parallel Plate Capacitor, final The plate is now negatively charged A similar process occurs at the other plate, electrons moving away from the plate and leaving it positively charged In its final configuration, the potential difference across the capacitor plates is the same as that between the terminals of the battery
Capacitance – Isolated Sphere Assume a spherical charged conductor with radius a The sphere will have the same capacitance as it would if there were a conducting sphere of infinite radius, concentric with the original sphere Assume V = 0 for the infinitely large shell Note, this is independent of the charge and the potential difference 4 / o e e Q Q R C ¶Qa V k Q a k = = = =

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Capacitance – Parallel Plates The charge density on the plates is σ = Q / A A is the area of each plate, which are equal Q is the charge on each plate, equal with opposite signs The electric field is uniform between the plates and zero elsewhere
Capacitance – Parallel Plates, cont.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern