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Lecture: 24 (iq21) Ch19 (review), and first part of Ch20

1. Selected hw-problems in Ch19-h1

a. 002

b. 009 (notice that only 3 compasses illustrated will be considered in ths problem)

c. 013: Surface charge distribution of a circuit with a battery and two resistors, where R1>>R2.

d. 014, 015 selected choices in these two questions will be discussed.

2. Selected topics related to Ch20-h1

a. Ohm’s law:

o Ohm’s law-I (without specification on dimensions): J=sigma E, where sigma=|q|nu, the conductivity of the matter.

o Ohm’s law II (with dimensions): V=IR, R=rho l/A, rho is the resistivity.

b. 002

c. 003

d. 017, 18 spherical capacitor

e. Time dependence of RC circuit.

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.