Fundamentals of Electricity and Charges in Matter

1. Chapter 15 OutlineHonors Physics Created for CVCA Physics By Dick Heckathorn 24 February 2K + 5

2. Father of Electricity • Ben Franklin • positive charge • charge on glass rubbed by silk • negative charge • charge on ebony rubbed by fur

3. Law of Electric Charges • Opposite electric charges attract each other. • 2. Similar electric charges repel each other. • 3. Charged objects attract some neutral objects.

4. Structure of Matter • 1. All matter – composed of atoms. • 2. Electric charges carried by: • electrons and protons • 3. Elementary Charge – charge of electron and proton. • 4. Neutrons – no electrical charge • 5. Are both negative & positive ions

5. Charge Movement • 1. Positive charge – proton, is located in the nucleus, thus not free to move. • 2. Negative charge – electron, free to move • 3. Therefore, all excess in charges in solids result either from an excess or deficit of electrons.

6. Broad categories of substances • Conductor – electrons are able to move freely from one atom to another in a solid. • Insulator – electrons are not free to easily move from one atom to another in a solid. • Liquids & gases: ‘+’ & ‘-’ can move

7. Convention • 1. Charged objects marked with ‘-’ have an excessive of electrons. • 2. Charged objects marked with ‘+’ have a deficiency of electrons. • 3. Number of ‘-’ or ‘+’ signs do not represent the actual number of • ‘-’ or ‘+’ charges on the object.

8. Convention • 4. Neutral objects are not marked with equal number of ‘-’ or ‘+’ signs but are shown with no ‘-’ or ‘+’ signs. • This does not agree with what your text does in some situations.

9. Charging by Friction • 1. There is a transfer of electron from one object to the other according to how tightly each are held to the positive charges in their nucleus.

10. Electrostatic Series • Add from other power point

11. Induced Charge Separation • a. Rub white rod with wool • b. With sphere near the white rod, touch sphere with finger making sure the sphere does not touch the white rod. • c. Check charge using the electroscope.

12. Induced Charge Separation Remove finger. Electrons move to opposite side. Positive charges remain near rod. Electrons escape from sphere Touch with finger. Remove rod. Bring sphere near negative strip. Induction Explanation

13. Induced Charge Separation • 1. Charges are rearranged on an object (A) by the presence of another charged object (B). • 2. Touching object (A) will allow electrons to flow onto or off it. • 3. The charge on object (A) will always be opposite the charge on object (B).

14. Charging by Contact • a. Rub white rod with wool • b. Touch sphere to white rod until it repels. • c. Check charge using the electroscope.

15. Charging by Contact Touch sphere to white rod. Remove white rod Charge of sphere same as rod

16. Electrical Units

17. Electrophorus - Remove plate from foam ‘-’ repelled from bottom to top of plate Foam rubbed with wool Finger touches plate Place plate on negative foam Charges rearrange Electrons leave plate Wool gives ‘-’ to foam Leaving ‘+’ behind Finger removed from plate

18. Electrophorus + Remove plate from foam Finger touches plate Place plate on negative foam Wool takes ‘-’ from foam Foam rubbed with wool Charges rearrange ‘-’ attracted to bottom of plate Leaving ‘+’ behind Electrons added to plate Finger removed from plate

19. Q Q Q Coulomb’s Law q d d The force is positive if the charge on both objects have the same sign and negative if the sign of each charge is different.

20. Coulomb’s Law

21. Coulomb’s Law Restrictions • 1. Objects need to be very far apart so that the charges are considered acting all from one point.

22. Problems • 1. Sample Problems p – 588 • 1 2 • 2. Practice Problems p – 589 • 1 2 3

23. Gravitational & Electrical Forces Force Attractive or repulsive Attractive Direction Range Infinity Infinity Relative Strength 1 1039

24. Force of Electron on Proton in a Hydrogen Atom Electrical

25. Force of Electron on Proton in a Hydrogen Atom • Gravitational

26. Force of Electron on Proton in a Hydrogen Atom

27. Problems • 1. Sample Problems p – 590 • 1 2 • 2. Practice Problems p – 592 • 1 2 3 • 3. End of Chapter Problems – 620 • 13 14 15 16 17 18 19

28. Q Q Q Electric Fields ‘є’ r The direction of the Electric Field is in the direction of the force on a positive test charge due to charge ‘Q’ that causes the electric field.

29. Electric Fields ‘є’ • Electric fields exert a force on an electrical charge that is in the field. The direction of the electric field is in the direction of the force on a positive test charge ‘q’ in electric field ‘Q’.

30. Problems • 1. Sample Problems p – 596 • 1 2 3 • 2. Practice Problems p – 597 • 1 2 3 4 5 6 7 • 3. End of Chapter Problems – 621 • 20 21 22 23

31. Electric Potential Energy ‘Ee’ Q q r The electric potential energy is zero when the two charged objects are an infinite distance apart.

32. Electric Potential Energy ‘Ee’ Q q q r ∞ If negative it means that the force between the two object is attractive. Work is done and thus energy is stored by moving them further apart.

33. Electric Potential Energy ‘Ee’ Q q q r ∞ If positive it means that the force between the two object is repulsive. Work is done and thus energy is stored by moving them closer together.

34. Electric Potential ‘V’ Q ∞ r Electric potential represents the amount of work necessary to move a unit test charge from rest at infinity to rest at any specific point in the electric field of ‘Q’

35. Potential Difference Q B A rB rA The potential decreases in the direction of the electric field and increases in the opposite direction.

36. Electric Field of Parallel Plates • If the charges plates are close together: • 1. The intensity is zero in the region outside the parallel plates. • 2. The intensity is constant everywhere in the space between the plates. • 3. The magnitude of the intensity depends only on the magnitude of charge on each plate. • 4. This is called a uniform electric field.

37. Parallel Plate Calculation - VAB d +

38. Problems • 1. Sample Problems p – 602 • 1 2 3 4 • 2. Practice Problems p – 603 • 1 2 3 4 • 3. End of Chapter Problems – 622 • 24 25 26 27 28

39. Electrical Formulae Force Field Potential Energy Potential

40. Electric Field Inside a Sphere • 1. Like charges dislike each other. • 2. On a conducting surface the want to get as far away from each other. • 3. Thus all charges end up on the outer surface. • 4. Thus, the electric field inside the sphere is zero.

41. That’s all folks!