2. Mechanisms for Transfer of Charge Restless Electrons

3. How do objects gain “static” charge? Friction –Rubbing two electrically neutral objects together can charge both objects – both gain OPPOSITE charge Conduction –Charged object TOUCHES another object – electrons jump from one to the other in an attempt to EQUALIZE the charge on both objects Induction –Charged object comes near another object WITHOUT TOUCHING – causes it to POLARIZE

4. Why is it the electrons that are usually transferred during charging? Electrons are much smaller (2000 X) than the protons so they are easier to move. Electrons are located outside the nucleus of the atom in the electron cloud. This makes them loosely connected to the atom and easier to remove.

5. Conductive Properties of Solids Conductors allow charge to flow through them easily high conductivity Insulators inhibit charge flow high resistivity rubber silicon wood pure water metals special metal alloys SUPER CONDUCTORS SEMI INSULATORS CONDUCTORS CONDUCTORS sea water

6. Friction This works best when two INSULATORS are rubbed against one another

7. Charging By Friction John Travoltage Balloons

8. Conduction Negative To Neutral -- Excess electrons exert repulsive forces on one another, causing them to move apart as much as possible BOTH now have the same charge!

9. Conduction Positive To Neutral ++ Electrons in the neutral object experience an attractive force. They neutralize some of the positive charge, leaving both with a lack of electrons BOTH now have the same charge!

10. Induction Negative To Neutral Polarization +- - Excess electrons exert force against nearby electrons in the neutral object

11. Induction Positive To Neutral Polarization + - + Electrons in the neutral object experience an attractive force, which pulls them closer to the charged object Balloons Again

12. Permanently Charging Two Spheres by Induction

13. Grounding Since the Earth is so large it can equalize charges from other objects very easily The Earth can equalize charge by: absorbing excess electrons from negatively charged objects giving free electrons to positively charged objects In either case, grounding a charged object makes it neutral One symbol that is often used to show that something is grounded is:

14. Charging One Sphere By Induction with Grounding

15. Electroscope - - - - - - - An electroscope is a device that detects CHARGE When the scope is CHARGED, the LEAVES at the bottom will REPEL one another The charged LEAVES exert force on one another, forcing them apart

16. Electroscope – negative cond. - - - - - - - Step 1 Negative rod touches neutral scope Step 2 Electrons spread out and charge plates Step 3 Scope is now negatively charged Step 4 Scope is grounded allowing electrons to escape Step 5 Scope is once again neutral – excess electrons are gone

17. Electroscope – positive cond. + + ++ - - - - - - Step 1 Positive rod touches neutral scope Step 2 Electrons leave scope because they are attracted to the positive rod Step 3 Scope is now positively charged Step 4 Scope is grounded – electrons from the ground are attracted to the positive scope Step 5 Scope is once again neutral – balanced charge is restored

18. Electroscope – negative ind. - + - - Step 1 Negative rod brought near grounded scope Step 2 Scope polarizes as electrons at the top try to move away from the charged rod. Step 3 Rod is removed – electrons are attracted back to the top and “re-neutralize” the electroscope.

19. Electroscope – positive induction + - - Step 1 Positive rod is brought near neutral electroscope Step 2 Electrons from the bottom of the electroscope are attracted to the positive rod – get pulled up. The leaves get a positive charge on them. Step 3 Rod is removed. Electrons are attracted back into the leaves by the protons, making the electroscope neutral again. ++

20. Electroscope – ind. with ground - + - ++ - - Step 1 Negative rod brought near grounded scope Step 2 Excess electrons from the rod force electrons from the scope into the ground. Step 3 Ground is removed while the rod is still nearby, keeping electrons from re-entering the scope Step 4 Scope now has a charge that is opposite to the charge on the rod Step 5 The rod is taken away and the positive charge remains on the scope

21. Electroscope – ind. with ground + - - - Step 1 Positive rod is brought near grounded scope Step 2 Electrons from the ground are attracted to the positive rod Step 3 Ground is removed, while the rod is still nearby, pulling on electrons and keeping them from escaping Step 4 Scope is now negatively charged – the opposite charge as that of the rod Step 5 Rod is taken away and the negative charge remains on the scope