Review

1. Review • Please fill in the charges on your entrance ticket…place + or – signs where they belong

2. Remember…+ charge does not mean protons…we don’t touch the nucleus Electricity only involves electrons or a lack of electrons - charge + charge http://www.youtube.com/watch?v=Gy9JRQAffbo

3. # 1 Conservation of Charge • In a neutral atom, there are as many _____ as _______, so there is no (net) charge on the atom If an electron is removed from an atom, the atom is no longer _______ (positive, negative, neutral) • Protons, electrons • Neutral

4. What does Conservation mean? The preservation of existing conditions

5. Conservation of Charge • An atom with more positive charges (protons)than negative are said to be ____ charged. • A charged atom is called a(n )_____. (ion, force, repulsion, attraction) • Positively • ion

6. What are the other 2 Law of Conservation we have mentioned in class? • 1) Law of Conservation of Energy…energy is neither created nor destroyed, it simply changes forms • 2) Law of Conservation of Momentum..momentum does not change unless an external force acts upon it

7. Conservation of Charge • The total amount of Electric Charge in a system does not change…. when particles are destroyed, equal numbers of positive and negative charges are destroyed. • First proposed by Benjamin Franklin • Most evidence indicates that the net charge in the universe is zero

8. #2 Free Electrons • Electrons in the (outer, inner) rings or shells of atoms are bound more loosely to the nucleus • Such electrons tend to break free from the nucleus and wander around amongst other nearby atoms • Such electrons are called free electrons

9. The youngest children in a family are similar to free electrons…held less tightly by the parents • http://www.youtube.com/watch?v=ZMhHzucl9lI

10. Free electrons • Such movement of these free electrons creates an electric current • Materials with large numbers of free electrons are called electrical conductors. They conduct electrical current.

11. # 3 Conductors • Movement of the electrons physically from one place to another is slow. • Transfer of the energy from one electron to another happens fast. • Metals are good conductors

12. #3 Insulators • Insulators have tightly bound electrons • Which make them poor conductors of electricity • Examples- rubber, glass, ceramic, wood, styrofoam, air

13. Main Idea • Whether a substance is classified as a conductor or an insulator depends on how t______ the atoms of a substance hold their e______. • Tightly, electrons

14. #4 Semiconductors • Some materials are good insulators (as good as glass) in their solid form, but become good conductors (as good as Copper) if even one atom in ten million is replaced with an “impurity” called doping • They can be made to behave as insulators and sometimes as conductors • AKA- transistors, LEDs, solar cells • They are the foundation of modern electronics

15. Semiconductors • Silicon and Germanium crystals are the most common semiconducting materials formicroelectronics. • Anything that's computerized or uses radio waves depends on semiconductors. • Clockwise from top: A chip, an LED and a transistor are all made from semiconductor material.  See more electronics parts pictures.

16. Silicon Valley • 1/3 of the companies relocated to Austin, Texas from Silicon Valley

17. #5 Superconductors • Discovered in 1911, by a Dutch physicist, at temperatures near absolute zero, certain metals acquire almost infinite conductivity (zero resistance). Once an electric current is established in a superconductor, the electrons flow indefinitely and a magnetic field is created • Uses: Superconducting magnets are some of the most powerful electromagnets known…used in MRI