# quiz4 - o where Q is the total charge σ=Q/A is the areal...

This preview shows pages 1–2. Sign up to view the full content.

September 15, 2009 QUIZ 4 PHY2054/3808 1. Two capacitors give an equivalent capacitance of 9 pF when connected in parallel and an equivalent capacitance of 2 pF when connected in series. What is the capacitance of each capacitor? The equations are Whose solutions are C 1 = 6 pF and C 2 = 3pF. 2. When two charges are separated to twice the distance between them, the force on one due to the other reduces by a factor of four. When the two (equally but with opposite sign) charged plates in a parallel plate capacitor are separated to twice the distance between them, what is the change in force exerted by one plate on the other. The electric field between the parallel plates of a capacitor is given by E= σ/ε o . In fact, if we want the force on the negative plate, we should consider only the electric field due to the positive plate (E= σ/2ε o ) and the force on the negative plate becomes F = QE=Q σ/2ε

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.

Unformatted text preview: o , where Q is the total charge, σ=Q/A is the areal density over area A of each plate. The most important conclusion here is that F does not involve the distance between the plates. The force is the same, given the charge and the area and does not change when the plates are pulled apart. This is true only if the charge on each plate remains the same i.e. the plates are not connected to a battery. If the plates are connected to a battery, then the potential difference remains (held to be) the same but the amount of charge on each plate changes. There is a simple calculation to show that if the distance between the plates is doubled, while connected to a battery, the force on one plate exerted by the other is reduced by a factor of four. The force varies as a square of the distance between the plates. 18 9 2 1 2 1 = = + C C C C 3....
View Full 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