Electric Force

1. Electrostatics Electric Force EQ: How can an object be charged and what affect does that charge have upon other objects around it? LO: We will identify the basic properties of an electric charge and learn how to apply Coulomb’s Law CT: I will differentiate between conductors and insulators and distinguish between the different methods of charging a material.

2. Electrostatics Electric Force pg. 62 EQ: How can an object be charged and what affect does that charge have upon other objects around it?

3. Electrostatics-the Basics • Electric charges at rest (static electricity) • Electric Force, which is a force between objects with charge, just as the gravitational force is a force between objects with mass.

4. The Basics-Atomic structure

5. The Basics- 2 types of charges A charge is present if there is an imbalance of protons and electrons - + + - + - electrons are migrants - constantly on the move and always ready to try out a new atomic environment or persuade other electrons to try out their atomic environment.

6. The Basics-checkpoint  ____ are the charged parts of an atom • a. Only electrons • b. Only protons • c. Neutrons only • d. Electrons and neutrons • e. Electrons and protons • f. Protons and neutrons

7. Neg Neg Neg Pos Pos Pos The Basics-the fundamental law Like charges repel; unlike charges attract.

8. The Basics-checkpoint Electrical forces ____. a. can cause objects to only attract each other b. can cause objects to only repel each other c. can cause objects to attract or repel each other d. have no effect on objects

9. The Basics-checkpoint Upon entering the room, you observe two balloons suspended from the ceiling. You notice that instead of hanging straight down vertically, the balloons seems to be repelling each other. You can conclusively say ... a. both balloons have a negative charge. b. both balloons have a positive charge. c. one balloon is charge positively and the other negatively. d. both balloons are charged with the same type of charge.

10. The Basics-conductors and insulators The movement of charge is limited by the substance the charge is trying to pass through. There are generally 2 types of substances. Conductors:Allow charge to move readily through it (metals such as copper, gold, aluminum) Insulators:Restrict the movement of the charge (plastic, rubber, glass) Charged conductor Charged insulator

11. The Basics-conductors and insulators • Semiconductors: Are materials characterized by electrical properties that are somewhere between those of insulators and conductors. A foundation of modern electronics • Superconductors: Are materials that will conduct electricity without any resistance when cooled below their critical temperature. Benefit-energy would not be lost. Downfall- cooling constraints.

12. The Basics-conservation of charge Electrons are never created nor destroyed, but are simply transferred from one material to another • No case of the creation or destruction of net electric charge has ever been found

13. The Basics-checkpoint A conductor differs from an insulator in that a conductor ________. a. has an excess of protons b. has an excess of electrons c. can become charged and an insulator cannot d. has faster moving molecules e. does not have any neutrons to get in the way of electron flow f. when charge is placed on a conductor, it redistributes to the outer surface.

14. The Basics-polarization Polarization is the separation of charge In a conductor, “free” electrons can move around the surface of the material, leaving one side positive and the other side negative. In an insulator, the electrons “realign” themselves within the atom(or molecule), leaving one side of the atom positive and the other side of the atom negative. Polarization is not necessarily a charge imbalance!

15. The Basics-Closing Task • Title pg. 63 “Electric Field Hockey • Answer the questions on the handout on pg. 63. Do not write on the handout

16. Electrostatics- Charging Methods • Friction – friction by rubbing • Induction –method used to charge an object without actually touching the object to any other charged object then grounding the conductor • Conduction - involves the contact of a charged object to a neutral object

17. negative -- -- positive + + + + Charging Methods-contact When a rubber rod is rubbed against fur, electrons are removed from the fur and deposited on the rod. Electrons move from fur to the rubber rod. The rod is said to be negatively charged because of an excess of electrons. The fur is said to be positively charged because of a deficiency of electrons.

18. positive glass + + + + negative - - - - silk Charging Methods-contact Which material gives up the electrons? Triboelectric effect

19. Charging Methods-induction Induction uses the influence of one charged object to “coerce” charge flow. Step 1. A charged rod is brought near an isolated conductor. The influence of the charge object polarizes the conductor but does not yet charge it. Step 2. The conductor is grounded to the Earth, allowing charge to flow out between it and the Earth.

20. Charging Methods-induction Step 3. The ground is removed while the charge rod is still nearby the conductor. Step 4. The rod is removed and the conductor is now charge (opposite of rod). An object charged by induction has the opposite sign of the influencing body. Notice that the original charged object does not lose charge. https://www.youtube.com/watch?v=-JsVZwc1dOo

21. Charging Methods-induction What is grounding?*Grounding means making objects neutral or uncharged*The ground serves as an infinite source to supply electrons to object or receive electrons from an object until the object has an equal amount of protons and electrons to be considered neutral. *Grounding with an inductor present allows the conducting object to obtain a charge rather than neutralizing it

22. Writing prompt In terms of electron movement, explain what is happening in Diagrams B and C above. Finally, state the charge acquired by the left and the right can as a result of this process.

23. Charging Methods-conduction When a charged conductor makes contact with a neutral conductor there is a transfer of charge. CHARGING NEGATIVELY CHARGING POSITIVELY Electrons are transferred from the rod to the ball, leaving them both negatively charged. Electrons are transferred from the ball to the rod, leaving them both positively charged. Remember, only electrons are free to move in solids. Notice that the original charged object loses some charge.

24. Charging Methods-conduction Writing prompt: Now consider the conducting charging of the person using a positively charged sphere. In terms of electron movement explain what is happening for the person’s hair to have static

25. Electric Forces and Fileds MICHAEL FARADAY (1791-1867) CHARLES COULOMB (1736-1806)

26. The Quantity of Charge The quantity of charge (q) can be defined in terms of the number of electrons The Coulomb (C) is the unit The Coulomb: 1 C = 6.25 x 1018 electrons 1/e Which means that the charge on a single electron is: 1 electron: e- = -1.6 x 10-19 C

27. Units of Charge The coulomb (selected for use with electric currents) is actually a very large unit for static electricity. Thus, we often encounter a need to use the metric prefixes. 1 mC = 1 x 10-6 C 1 nC = 1 x 10-9 C 1 pC = 1 x 10-12 C

28. constant Charges (C) electrostatic force (N) Distance (m) The Electrostatic Force-Coulomb’s (C) Law The force of attraction or repulsion between two point charges is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them. k - The constant of proportionality = 8.99 x 109 Nm2/C2. COULOMB’S LAW OF ELECTROSTATIC FORCE A negative force is attractive, and a positive force is repulsive. The sign (+ or –) is different from a vector direction (left or right)

29. -5 C +3 C + - 2 mm q q’ The Electrostatic Force-Coulomb’s (C) Law Example A –5 C charge is placed 2 mm from a +3 C charge. Find the force between the two charges. F Draw and label givens on figure: r Note: Signs are used ONLY to determine force direction.

30. The Electrostatic Force-Coulomb’s (C) Law EXAMPLE 1 - Find the force between these two charges EXAMPLE 2 - Find the net force on the left charge

31. The Electrostatic Force-Coulomb’s (C) Law EXAMPLE 3 - Find the net force on the upper left charge 425 N, 58˚

32. Electric Field Strength Field Theory Visualizes Force At A Distance DEFINITION OF GRAVITATIONAL FIELD DEFINITION OF ELECTRIC FIELD q0 is a small, positive test charge Electric field is a vector quantity SI unit of electric field click for applet

33. constant charge electric field distance Electric Field Lines Single Point Charges POSITIVE CHARGE NEGATIVE CHARGE Density of field lines indicates electric field strength Inverse square law obeyed click for applet Definition of E Field for single point charge

34. Electric Field Lines Electric fields for multiple point charges POSITIVE AND NEGATIVE POINT CHARGES TWO POSITIVE POINT CHARGES OPPOSITE MAGNETIC POLES ALIKE MAGNETIC POLES

35. Summary of Formulas: Like Charges Repel; Unlike Charges Attract. 1 mC = 1 x 10-6 C 1 electron: e- = -1.6 x 10-19 C 1 nC = 1 x 10-9 C 1 pC = 1 x 10-12 C

36. Draw an atom and label the protons, neutrons and electrons Which of these particles is the easiest to remove? Bell Ringer