LECTURE 12 Announcements lectures 9-10 available online solutions to Chapter 25 problems available online Announcements lectures 9-10 available online solutions to Chapter 25 problems available online Pick up reading assignment 5 graded reading quiz #2 lecture notes Pick up reading assignment 5 graded reading quiz #2 lecture notes

Course Questionnaire “ What do you LOVE about this class?” Lecture notes (in class & web) Interactive lectures, student involvement, encouragement of class participation “Demos are cool” In class problem solving & discussion Example problems solved step by step Concept tests “Material is difficult but interesting” Review session Availability of help, “can ask question” Labs are interesting

Course Questionnaire “What do you HATE about this class?” Reading Quizzes “unfair, scary” “Being made to go to the front when I don’t have a damn clue what’s going on.. (although it’s probably good for me)” Always the same people go up “explain again after they are done” Time consuming hw, labs Tutorials: do only one problem, need to ask more questions Early morning time slot Lecture too fast Exam: 50 min only, too few problems Little explanation before questions

Course Questionnaire “ If you were teaching what would you do?” “If you could change one thing, what would it be?” “Keep on doing things the same way” “Keep the class participation & overhead. No straight lecturing” no reading quizzes “I guess I wouldn’t call on people, but no one raises their hands so I can understand” call more people from the list increase interaction between students make homeworks due Wednesday, change tutorial change time: “I hate 9:35 classes” More demos “do not scare us that they’ll be on the test” post test-like problems less time-consuming hw outside class review sessions online quizzes

Clarifications & Possible changes More demos (hard to find “good ones”) Reading Quizzes –do not (should not) test understanding, only whether you read the assignment or not; –quizzes have little impact on your overall grade Class participation is essential –IT IS OK not to know the answer to the question: if asked, explain what is confusing; –Will use class list/random calling as last resort –(maybe) give credit for “going up front” and successfully solving a problem Move HW due date for Wednesday (already implemented), Tutorials (old format from P131) discuss (do not solve!) HW; solve suggested problems.

A dielectric is inserted between the plates of a capacitor. The system is then charged and the dielectric is removed. The electrostatic energy [U=(1/2)CV 2 ] in the capacitor is 1.greater than 2.the same as 3.smaller than it would have been if the dielectric were left in place Charges on the capacitor plate (blue) are attracted to the bound surface charges of the dielectric. Work must be invested to remove the dielectric, and this work is stored as electrostatic energy. Another way: as the dielectric is removed, k=1: U increases

Charge conduction in a metal Current = charge across A per unit time charge carried by small particles, electrons electrons: collide with impurities, lattice Electrons encounter resistance “pinball model” for resistance See demo on DVD

Resistance and Ohm’s law The bigger the field E, the larger the current I See demos on DVD resistance depends on temperature Question: Can you explain qualitatively the temperature dependence of R using the Pinball model? Question: Can you explain qualitatively the temperature dependence of R using the Pinball model?