Physics 242 – Electric Charges

1. Quantum Mechanical Model Bohr Model of Atom http://csep10.phys.utk.edu/astr162/lect/light/bohr.html http://www.physics.ucla.edu/~dauger/orbitals/ Materials with equal numbers of neg. and pos. charge are said to be electrically neutral. Physics 242 – Electric Charges Types and Sources of Electric Charge Two kinds of electric charge – positive negative protons electrons

2. Physics 242 – Electric Charges Types and Sources of Electric Charge THANKS BEN! Ben Franklin actually did a great deal of experimentation in the area of electricity. However, Ben Franklin chose the wrong sign convention for charge – it has stuck ever since.

3. Physics 242 – Electric Charges Proton Decay • p → e+π0 Properties of Electric Charge • Charge is quantized. • Positive and Negative charges have same magnitude • e = p = 1.6 x 10-19 C • SI unit of charge is the Coulomb • Charge is conserved. http://www-personal.umich.edu/~jcv/imb/imb.html http://www.wikipedia.org/wiki/Proton_decay

4. Physics 242 – Electric Charges Different elements will have different types of bonds – different strengths. Insulators Conductors Electrons are free to move about the material Electrons are bound to the atoms - can’t move (conduct). Atoms and Materials Classification of Materials – Conductors, Insulators, Semiconductors

5. Positive (+) Electrostatic Voltages Air Means of Static Generation 10 – 20 % Humidity 65 – 90 % Humidity Human Hands Walking across carpet 35,000 1,500 Triboelectric Series Rabbits Fur Walking across vinyl floor 12,000 250 Glass Worker at bench 6,000 100 Human Hair Vinyl envelopes for work instructions 7000 600 Mica Common poly bag picked up from bench 20,000 1,200 Wool Cats Fur Silk Careful when you fill up your gas tank! Aluminum http://esda.org/esdbasics1.htm Paper Cotton Rubber Balloon Hard Rubber Gold/Platinum Polyester Vinyl Saran Wrap Negative (-) Physics 242 – Electric Charges How do we charge an object? A. Tribocharging - Charging by rubbing

6. On non-symmetric objects, charge collects at sharp points. On symmetric objects, charge distributes uniformly Insulators – charge cannot move, so it remains localized around the contact region. Physics 242 – Electric Charges How do we charge an object? A. Tribocharging - Charging by rubbing Conductors – charge will distribute around the surface to try until equilibrium is achieved. - charge only resides on surface, not inside.

7. Charging by induction (two conductors) Charging by induction (1 conductor and ground) Physics 242 – Electric Charges How do we charge an object? B. Induction – Inducing a charge without touching. Conductors Charge is physically moved in/on the materials.

8. +3q +3q -3q +3q +3q • Outside the conductor, the net charge is +3q • Sphere equivalent to a point charge • Positive charge doesn’t move, neg. charge • does all the moving. +3q Physics 242 – Electric Charges Conductors – An Example

9. Free Standing Atoms are randomly oriented Charge does not actually move In/on the insulator – redistributes. Polarizes the material. Physics 242 – Electric Charges How do we charge an object? B. Induction – Inducing a charge without touching. Insulators