AC/DC plus Friday HMWK/Quiz, exam date, Electric Power

Today in class we discussed direct current and alternating current.  (notes below) 

We also went over answers to the weekend homework and you had the chance to correct answers.

We have three optional assignments expiring tomorrow at midnight and one that is good until next Monday; last minute emails may be sent to my school email address.  See older posts on this page for more info.

Homework that will be posted tomorrow and due Thursday:  p. 418#1-14 (sketch cartoon of graph on #14), 17,19, 21-25.  

There will be a quiz on Electricity this Friday.  We will learn some topics and concepts with magnetism next week and have an exam over electricity and magnetism next Thursday 

Alternating and Direct Current 

Direct Current (DC)

•      Continuous current in one direction

•      Electrons move from the - side of a circuit to +

•      e^- move slowly, often < 1mm per min.

•      Batteries provide DC (& are charged by DC)

Alternating Current (AC)

•      Charge moves back and forth

•      No net movement of electrons

•      In the US, our electricity cycles 60x per second.

–  “120VAC, 60Hz” means 120 Volts of AC, alternating at 60 Hertz (cycles/sec)

•      AC can be used with transformers to change voltages up or down.

•      Most of our appliances use DC, but AC is used for transmission to our homes

–  High voltage = lower power loss through resistance - made possible by alternating current.

Electric Power: how fast electrical energy is converted into other forms  

Units are Watts  (Joules/sec)

Equation:  P = I * V

A 60W light bulb uses 60J of electricity per second, and makes thermal E and light.