3. 7.2 – Electric Force

4. Electric Force Force – a push or a pull
Contact Forces – a force when objects are touching
Action-at-a distance Forces – a force can be applied without objects touching.

5. Laws of Static Electricity
Opposite charges attract.
Like charges repel.
Neutral objects are attracted to charged objects.

6. Charging by Conduction
The process of transferring charge between two objects by touching or rubbing (creating friction).
Charging by conduction leaves an object (i.e. an electroscope) with a residual charge IDENTICAL to that of the charging rod.

7. Charging by Induction
The process of rearranging electrons on a neutral object by bringing a charged object close to it (but not touching it).
A positive rod will induce electrons to migrate to the knob.

8. Transferring Static Electricity
Conduction:
A charged object touches another object and transfers electrons
Induction:
A charged object comes near another object and a charge results

9. Measuring Static Electricity
Use an electroscope
Super Cheesy Video!!

10. Attraction of Neutral Objects
Rubbing a balloon on your hair leaves negative charges on the balloon. The balloon is an insulator so the charge remains in one place on the balloon.
When you put the ball against a wall, it repels the negative charges in the wall. Now that area of the wall is positively charged and attracted to the negatively charged balloon.

11. Photocopiers!
1. You place the document you want to copy upside down on the glass
2. An extremely bright light scans across the document. Much more light reflects off the white areas (where there is no ink) than off the black, inked areas.
3. An "electrical shadow" of the page forms on the photoconductor. The photoconductor in a photocopier is a rotating conveyor belt coated with a chemical called selenium.
4. As the belt rotates, it carries the electrical shadow around with it.
5. An ink drum touching the belt coats it with tiny particles of powdered ink (toner).
6. The toner has been given an electrical charge, so it sticks to the electrical shadow and makes an inked image of the original page on the belt.

12. 7. A sheet of paper from a hopper on the other side of the copier feeds up toward the first belt on another conveyor belt. As it moves along, the paper is given a strong electrical charge.
8. When the paper moves near the upper belt, its strong charge attracts the charged toner particles away from the belt. The image is rapidly transferred from the belt onto the paper.
9. The inked paper passes through two hot rollers (the fuser unit). The heat and pressure from the rollers fuse the toner particles permanently onto the paper.
10. The final copy emerges from the side of the copier. Thanks to the fuser unit, the paper is still warm. It may still have enough static electric charge to stick to your pullover. Try it (but make sure the ink is dry first).
Video