lect08 - Physics 227: Lecture 8 Dielectrics, and Capacitors...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
Physics 227: Lecture 8 Dielectrics, and Capacitors Lecture 7 review: Capacitors come in many sizes and shapes Q=CV - charge ±Q on the two plates, voltage V across them Energy Stored = U = Q 2 /2C = CV 2 /2 u = U/Volume = ½ε 0 E 2 In a circuit, capacitors in parallel add, capacitors in series add inversely Friday, September 23, 2011
Background image of page 1

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

View Full DocumentRight Arrow Icon
Capacitive Iclicker Puzzle Student A says: The plates of my parallel plate capacitor attract each other, so I have to hold them to keep them apart. Student B says: The plates of my capacitor repel each other, so I have to hold them to keep them together. Who is right? A. A. B. B. C. Both A and B. D. Neither. E. This does not make sense. Remember your answer to this brain teaser. We will Fnd out the right answer in the next few slides. Friday, September 23, 2011
Background image of page 2
Changing Capacitance A parallel plate capacitor has Q = CV with capacitance C = ε 0 A/d. How can we change the capacitance? The easy way is to move the plates closer together or farther apart. It is natural to think that, since the plates have opposite charge, the forces between them are attractive. Student A is right!? Let’s look in more detail at what happens when the plates come closer together . .. Since Q is the same, the electric Feld is constant, so the energy density u = ½ε 0 E 2 is constant. Constant u with decreasing volume less stored potential energy, so U is being converted into kinetic energy of the plates. It all makes sense, student A was right ! The force is attractive, the plates would naturally come together, they have to be held apart. Friday, September 23, 2011
Background image of page 3

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

View Full DocumentRight Arrow Icon
Changing Capacitance - Not so fast A parallel plate capacitor has Q = CV with capacitance C = ε 0 A/d. We made an assumption: ``
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/27/2011 for the course PHYSICS 750:227 taught by Professor Ronaldgilman during the Fall '11 term at Rutgers.

Page1 / 16

lect08 - Physics 227: Lecture 8 Dielectrics, and Capacitors...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online