Electric force and Electric Fields

1. Electric force and Electric Fields Introduction and Review http://videos.howstuffworks.com/discovery/7102-electromagnetic-pulse-bomb-video.htm http://www.msnucleus.org/membership/slideshows/electricity.html http://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#c1

2. Electric charge • Electric charge is a property of certain subatomic particles, which gives rise to and interacts with the electromagnetic force, one of the four fundamental forces of nature. • Charge originates in the atom, in which its most familiar carriers are the electron and proton.

3. Electrons are the particle that is transferred in transfer of charge

4. Law of conservation of charge • Charge is a conserved quantity, that is, the net charge within an isolated system will always remain constant regardless of any changes taking place within that system. • Within the system, charge may be transferred between bodies, either by direct contact, or by passing along a conducting material, such as a wire. • Like charges: repel • Unlike charges: attract

5. Insulators and conductors Conductor • A material where many electrons are bound loosely to the nuclei and can move freely about the material • When a conductor is given a negative charge, the excess electrons will spread themselves over the whole conductor • Conductor examples include: • most metals • aqueous solutions of salt • water • the human body

6. Insulators and conductors • A material where there are almost no loosely bound electrons • Can be charged, but charge does not distrbute over the material • Examples of insulators include: • Plastics • Styrofoam • Paper • Rubber • Glass • dry air

7. Semiconductors • Materials that have a few free electrons • Often have interesting properties such as: • Only conducting electrons in one direction • Only conducting when illuminated by light • Examples include: • Silicon • Germanium • carbon

8. The division of materials into the categories of conductors and insulators is a somewhat artificial division

9. Charging objects • Friction- charge is separated- each object receives an equal and opposite charge • Conduction- touching a charged object to an uncharged object- ex. Touching a negatively-charged rod to a neutral sphere- the sphere becomes negatively charged • Induction-the charged object does not actually touch the neutral one- but it is brought near it, causing a re-distribution of charge on the neutral object

11. DEMO: INDUCTION AND CONDUCTION • Charged ruler near pieces of paper: • What happens? • The ruler induces an opposite charge on the paper (induction) • The paper is then attracted to the ruler • The paper is charged with the same charge as the ruler- by conduction • Because the ruler and paper are now sharing the same charge, they repel, and the paper flies off the ruler! http://www.physicsclassroom.com/class/estatics/U8l2a.cfm

12. Electroscope • A device that detects electric charge • Demo:

13. Class questions! • http://www.physicsclassroom.com/class/estatics/U8l2b.cfm

14. Static electricity • The informal term static electricity refers to the net presence (or 'imbalance') of charge on a body, • usually caused when dissimilar insulatorsare rubbed together, transferring charge from one to the other.