1. Electrostatics 2

2. Structure of matter I.All material objects are composed of atoms. A.There are different kinds of atoms known as elements. B.These elements can combine to form compounds. C.Different elements and compounds have distinctly different properties. D.Material objects are composed of atoms and molecules of these elements and compounds, and are responsible for the different properties of different materials. http://www.rsc.org/periodic-table

3. Structure of matter II.Each atom consists of a nucleus and a vast region of space outside the nucleus. A.Electrons are present in the region of space outside the nucleus. B.They are negatively charged and relatively-weakly bound to the atom. C.Electrons are often removed from and added to an atom by everyday occurrences. If the proton were the size of a golf ball, the electron would be a mile away. If an atom were the size of a penny, a penny would be the size of the moon.

4. Structure of matter III.The nucleus of the atom contains positively-charged protons and neutral neutrons. A.These protons and neutrons are not removable by everyday methods. B.It requires some form of high-energy nuclear occurrence to disturb the nucleus and dislodge its positively-charged protons. C.With the exception of sunlight, you do not likely have much experience with these high- energy occurrences.

5. Two types of charges By convention, we call charges ‘positive’ and ‘negative’. Charge on glass rod = positive = lose electrons This convention is entirely arbitrary and comes to us courtesy of Benjamin Franklin Charge on amber (or rubber or plastic) = negative = gain electrons

6. Characteristics of charge Seems to leak away Especially in humid air Transferrable from one object to another by contact Is highly mobile on metallic objects Etc.

7. Conservation When objects we rub objects, Franklin hypothesized that the charge gained by one object is equal to the charge lost by the other. In every experiment conducted since, his hypothesis has been supported: electric charge is conserved. Though, if you are not careful, charge can and will transfer to water molecules in the air. Have you noticed that hair is frizzier on dry days? Electric charge is not created or destroyed.

8. Attraction & repulsion Opposite charges attract.Like charges repel.

9. Build up of charge Triboelectricity: charging by friction Induction : charging by touching Polarization : charging by proximity

10. Triboelectricity Different objects have different levels of ‘enthusiasm’ for picking up or letting go of stray electrons. Your rubber-soled shoes become more positively charged (and therefore so do you) while polyester carpet becomes more negatively charged. When you touch the door knob, the charge imbalance quickly rebalances. You feel this rebalancing as a shock. John Travoltage

11. Induction: charging by touch If you touch a neutral, metal rod with a charged metal object, the rod acquires a charge. The electrons in the neutral object race into the positively-charged object (the one with fewer electrons), leaving fewer electrons in the formerly neutral object.

12. Polarization If you cut a neutrally- charged metal rod in two, both halves will be neutral. If you cut a neutrally-charged metal rod in two while holding a charged object near one end, both halves will have a charge. If you bring a charged object near an uncharged object, the electrons in the uncharged object are attracted or repulsed.

13. Ways to have fun with static electricity With triboelectricityWear the appropriate clothing, slide across the appropriate surface, then touch someone Entice a cat to explore a box of packing peanuts With inductionMake a Leyden jar.Leyden jar With polarizationTrain a soda can to chase a plastic ruler Stick a balloon to a wall

14. http://ffden-2.phys.uaf.edu/211_fall2010.web.dir/Levi_Cowan/lightning.html Less fun but very interesting….

15. Electroscope: “seeing” electricity Notice the electrons are attracted to the positively-charged rod and, when the rod touches the knob, the electrons leave the electroscope. The electroscope is positively charged and the leaves of the electroscope repel each other. http://paer.rutgers.edu/PT3/experiment.php? topicid=8&exptid=145

16. How do we measure charge? Requires measurement of interaction Measurement of interaction = measurement of force French physicist, Charles Coulomb (1736 – 1806) discerned that:  charge  attraction or repulsion  distance   attraction or repulsion Here Here is a (long, but interesting) explanation and re-creation of his experiment.

17. Coulomb’s Law

18. Quantifying electrostatics

19. What’s a coulomb? One C, Coulomb, is defined as the amount of charge that leads to a 9 billion N (~1 million tons) force exerted on charged objects 1 meter apart. That is a uselessly big number. Rubbing a comb with wool: 10 -6 C A single electron: e = 1.6 x 10 -19 C

20. Example What force does a proton (+e) exert on an electron (-e) which is 5.3 x 10 -9 m away? G q 1 = 1.6 x 10 -19 C q 2 = -1.6 x 10 -19 C d = 5.3 x10 -9 m U F = ? E S S F = 8.2 x 10 -8 N

21. Example Two charges are 5.0 x 10 -5 m apart: q 1 = 3 x 10 -6 C, q 2 = 9 x 10 -6 C. Which exerts a greater force on the other? G q 1 = q 2 = d =d = U F = ? E S S F =