Thursday's HMWK: Read p. 400-405; p. 405#1-7. again, some classes will have random quizzes.
Thursday, 2-3, we went over answers from last week's homework. Some people refused to correct answers as we went over them; this explains any less-than-perfect grades.
In class, we played with the Wimshurst machine again; this time inducing a metallic ball and having it move according to electric forces on it, which helped us visualize the electric field around charges.
Notes: electric field lines - Electric field is the area where electric forces act, and the field lines are a visual representation of the strength and direction of the field. To draw field lines, just visualize the direction of the force on a positive charge at a point, then draw an arrow. Some excellent explanations and images are here (we drew several examples in class).
On Friday we discussed how the Van de Graaff generator works and how lightning rods work, and several people from each class got to see the difference between a pointed object that dissipates charge gradually (a hissing sound is heard) or a round object that charge accumulates on until a large discharge occurs.
I re-demonstrated charging by induction with a conductive balloon near the Van de Graaff; the balloon initially was attracted because the electric field of the Van de Graaff moved around electrons in the balloon, then the attractive (opposite) charge was nearest the Van de Graaff, and caused the balloon to attract. When the balloon touched the Van de Graaff, electrons were transferred and both objects obtained the same charge, and they repelled. Afterward I held my hand out and the balloon induced a charge on me, attracted to me, and bounced back and forth from me to the Van de Graaff as an electron shuttle.
Monday's class was used for playing with the Van de Graaff; you don't get many opportunities to to so otherwise and I'm not about to deprive you.
Highlights:
-charging people who are on an insulating platform (plastic stool) and having their hair stand on end; it was the same charge as they were so it repelled.
-Inducing charges on passersby and feeling lightning pass from one person to another (ouch!)
-Using a fluorescent tube light to pass sparks through as a path to ground, and watching the excited electrons make the light glow like a light saber from Star Wars... Not to mention feeling the impact of the electric field's force.
Today (Tuesday) we discussed the bicentennial (200yrs) since New Madrid's last of 4 big quakes (Dec 1811 to Feb 7, 1812) (7.7 estimated Richter - Mercalli must be used since Richter wasn't born until ~1900). Shook most of the midwest and was felt on the East Coast. Would devastate Memphis (and much of STL) if it happened again today. Be prepared!
Our activity was involving some basic electric concepts and experimentation: we played with Christmas tree lights and AA cells ("batteries"). Students were able to light a single bulb, find other conductors with the bulb/cell combination, light multiple bulbs with 2 or more cells, and increase the voltage for each light by using parallel circuits. A few folks were able to make REALLY bright displays; some even burned out lights!
Tomorrow we'll have notes and more playing with circuits to back up what you will learn.
Notes: electric field lines - Electric field is the area where electric forces act, and the field lines are a visual representation of the strength and direction of the field. To draw field lines, just visualize the direction of the force on a positive charge at a point, then draw an arrow. Some excellent explanations and images are here (we drew several examples in class).
On Friday we discussed how the Van de Graaff generator works and how lightning rods work, and several people from each class got to see the difference between a pointed object that dissipates charge gradually (a hissing sound is heard) or a round object that charge accumulates on until a large discharge occurs.
I re-demonstrated charging by induction with a conductive balloon near the Van de Graaff; the balloon initially was attracted because the electric field of the Van de Graaff moved around electrons in the balloon, then the attractive (opposite) charge was nearest the Van de Graaff, and caused the balloon to attract. When the balloon touched the Van de Graaff, electrons were transferred and both objects obtained the same charge, and they repelled. Afterward I held my hand out and the balloon induced a charge on me, attracted to me, and bounced back and forth from me to the Van de Graaff as an electron shuttle.
Monday's class was used for playing with the Van de Graaff; you don't get many opportunities to to so otherwise and I'm not about to deprive you.
Highlights:
-charging people who are on an insulating platform (plastic stool) and having their hair stand on end; it was the same charge as they were so it repelled.
-Inducing charges on passersby and feeling lightning pass from one person to another (ouch!)
-Using a fluorescent tube light to pass sparks through as a path to ground, and watching the excited electrons make the light glow like a light saber from Star Wars... Not to mention feeling the impact of the electric field's force.
Today (Tuesday) we discussed the bicentennial (200yrs) since New Madrid's last of 4 big quakes (Dec 1811 to Feb 7, 1812) (7.7 estimated Richter - Mercalli must be used since Richter wasn't born until ~1900). Shook most of the midwest and was felt on the East Coast. Would devastate Memphis (and much of STL) if it happened again today. Be prepared!
Our activity was involving some basic electric concepts and experimentation: we played with Christmas tree lights and AA cells ("batteries"). Students were able to light a single bulb, find other conductors with the bulb/cell combination, light multiple bulbs with 2 or more cells, and increase the voltage for each light by using parallel circuits. A few folks were able to make REALLY bright displays; some even burned out lights!
Tomorrow we'll have notes and more playing with circuits to back up what you will learn.
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