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# Electricity & Magnetism Conceptual Physics acloutier copyright

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Conceptual physics electricity and magnetism

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### Electricity & Magnetism Conceptual Physics acloutier copyright

1. 1. ELECTRICITY & MAGNETISM CONCEPTUAL PHYSICS Ann C Cloutier copyright 2011
2. 2. Coulomb’s Law Like charges repel, unlike attract Coulomb’s laws the relationship between any two objects following the inverse square law <ul><li>Isaac Newton’s Law of Gravity </li></ul><ul><li>the Universal Gravitational Constant is similar to Coulomb’s Law </li></ul><ul><li>F = G m1m2 </li></ul><ul><li>d ² </li></ul><ul><li>Coulomb’s Law states that for charged particles or objects that are small compared with the distance between them, the force between the charges varies directly as the product of the charges and inversely as the square of the distance between them </li></ul><ul><li>Force , Charge Distance </li></ul><ul><li>F = k q1 q2 </li></ul><ul><li>d² </li></ul><ul><li>dividing by d ² is the inverse square laws </li></ul>
3. 3. Like charges repel, unlike charges attract <ul><li>Unlike gravity’s force, electrical forces can be attractive or repulsive </li></ul>
4. 4. Electrons are negatively charged particles Protons are positively charged particles <ul><li>More electrons = negatively charged force </li></ul><ul><li>More protons = positively charged force </li></ul><ul><li>The electrical charge is greater than the gravitational force </li></ul><ul><li>F e = 8.2 x 10 -8 N = 2.2 x 10 39 </li></ul><ul><li>F g = 3.7 x 10 – 47 N </li></ul><ul><li>The electrical forces subatomic particles exert on one another are so much stronger than their mutual gravitational forces that gravitation (GRAVITY) can be completely neglected </li></ul>
5. 5. Electrons move easily in good conductors and poorly in good insulators <ul><li>Power lines have metal because of its conductivity </li></ul><ul><li>glass and plastic are good insulators, so are germanium and silicon because of their pure crystalline structures </li></ul><ul><li>Semiconductors can behave both ways, as conductors and as insulators </li></ul><ul><li>thin layers of semiconducting between materials make up transistors </li></ul><ul><li>computer, digital media players, various electrical appliances are some examples </li></ul>
6. 6. FRICTION and CONTACT are two ways to transfer electric charges <ul><li>Can you list three examples that set of sparks of electricity ? </li></ul><ul><li>Comb your hair on a dry day; </li></ul><ul><li>take clothes out of the dryer and pull apart fused socks; </li></ul><ul><li>drag your feet on rug and touch an electrical outlet </li></ul>
7. 7. Charging by Induction occurs in thunderstorms <ul><li>Lightning is static electricity </li></ul><ul><li>The ground has a positively charged generated on the surface </li></ul><ul><li>The cloud has a negatively charged bottom and a positively charged top </li></ul><ul><li>Lightning is an electrical phenomenon </li></ul><ul><li>This was proven by Ben Franklin and his kite experiment </li></ul><ul><li>Franklin found that charges flow to sharp points more readily = the invention of the lightning rods </li></ul>
8. 8. Charged Polarization can occur in insulators that are near a charged object <ul><li>there is a rearrangement of charged particles within an atom and the molecules themselves </li></ul><ul><li>one side of the atom or molecule is induced to be slightly more negative or positive than the opposite side </li></ul><ul><li>this makes the atom or molecule to become electrically polarized </li></ul><ul><li>the atoms or molecules near the surface all become aligned this way </li></ul>
9. 9. Microwave ovens <ul><li>Would not work without the presence of dipoles in the food (usually water molecules) </li></ul><ul><li>This is why they work through foam, paper, ceramic plates with no effect </li></ul><ul><li>Microwaves also reflect and bounce off conductors with no effect </li></ul><ul><li>Microwaves energize water molecules </li></ul><ul><li>Cooking food is essentially making water molecules oscillate and flip-flop which increases thermal motion in food </li></ul>
10. 10. Parts of a microwave
11. 11. Microwaves 10 - ²
12. 12. Water is an electric dipole molecule > the charges are not even, water is a little bit more negative on one end Water is a polar molecule with opposite charges on opposite sides
13. 13. The end… may the force be with you