Tuesday, May 6, 2008

Many students absent due to IB History test.

Went over RA 22.1

Introduced Ohm's Law: I = V/R
Showed how to find equivalent resistances for series (one after the other with a single path for current) and parallel (same potential difference across each element).

Showed demo of Christmas tree light hooked up in series and parallel. Investigated what happened to the brightness of the lights.

Derived P = I*V = I^2 *R = V^2/R

Talked about 60W and 100W light bulbs. Using them in parallel showed that the 100W light bulb has less resistance.

In series, the 60W light bulb would burn brighter since it has a higher resistance, would have a greater potential difference across it, and would dissipate more power.

Students worked problem 9 (combinations of resistors in series and parallel) in class. Assigned problems 1-8 (as well as 9 if they didn't finish) for homework.