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Lecture: 23 (iq20) Microscopic picture of a circuit

1. A simple circuit: Macro vs micro descriptions

2. Drude model and drift velocity Clicker 23.1

3. Mechanical battery and steady decreasing surface charge density. Clicker 23-2

4. Grading in surface charge density leads to field in the center of the wire. Clicker fig19.19.

5. Steady state of a current flow in a circuit

a. One loop: i maintains the same value throughout

b. Node: i_in=i₁+i₂

6. Examples

a. Loop equations and node equations Kirchhoff’s rules.

b. Simple circuit

c. Example with a simple series connection

d. Example with a simple parallel connection

e. Example with 4 identical bulbs

Announcement:

Midterm 2: Class average is 67.

o Reminder: How to determine the letter grade you made for this midterm?

o Find you scaled score which is located near the bottom of the grading page.

o Two letter grades for each exam:

§ letter grade-1 based on % cutoffs.

§ Letter grade-2 based on scaled score cutoffs.

o The letter grade you have made for this exam is the higher of the two letter grades, if there is a difference.

Redo mt2: Due time this coming Sunday, 11:30pm, 3/10.

o Discuss your performance-- Come to talk to me during my office hours, or other time by appointment.

No office hour today. If you want to see me today, please talk to me immediately after the class.