4/7/06 Capacitors & Diodes Monday’s Reading:

•Section 12.2: Audio Players (pp. 404 – 411);

stop at “The Audio Player’s Computer”.

Upcoming Reading Assignments:

•Section 13.1: Radio (pp. 423 – 431) •Section 13.2: Microwave Ovens (pp. 432 – 438) •Section 14.1: Sunlight (pp. 445 – 453) •Section 14.2: Discharge Lamps (pp. 454 – 463) •Section 14.3: Lasers and LEDs (pp. 464 – 470) •Section 15.1: Cameras (pp. 478 – 488) •Section 15.2: Optical Recording and Communication (pp. 489 – 497)

Capacitors Example: (Chapter 12, Exercise 9, p. 419) Two capacitors are identical except that one has a thinner insulating layer than the other. If the two capacitors are storing the same amount of separated electric charge, which one will have the larger voltage difference between its plates?

Example: (Chapter 12, Exercise 11, p. 419) Suppose a battery is transferring (negative) charges from one plate of a capacitor to the other. Why does the work that the battery does in transferring a charge increase slightly with each transfer?

Quantum Physics

•Wave-Particle Duality •Energy Levels •Pauli Exclusion Principle

Energy Levels in a Solid

Energy Levels in a Solid Conductor Insulator Photoconductor

Semi-conductors and p-n junction Start with good insulator Add small impurity that “opens” up some “space” in the valence band; P(ositive)-type or p-type Add small impurity that “add” some electrons to conduction band; N(egative)-type or n-type

Example: (Chapter 12, Exercise 5, p. 419) Thermal energy can shift some of the electrons in a hot semiconductor from the valence levels to the conduction levels. What effect do these shifts have on the semi-conductor’s ability to conduct electricity?

Semi-conductors and p-n junction Start with good insulator Add small impurity that “opens” up some “space” in the valence band; P(ositive)-type or p-type Add small impurity that “add” some electrons to conduction band; N(egative)-type or n-type Taken from howstuffworks.com

http://electronics.howstuffworks.com/led1.htm

Biasing the Junction