1. Advanced Physics Chapter 16 Electric Charge and Electric Field

2. 16-1 Static Electricity16-1 Static Electricity 16-2 Electric Charge in the Atom16-2 Electric Charge in the Atom 16-3 Insulators and Conductors16-3 Insulators and Conductors 16-4 Induced Charge: the Electroscope16-4 Induced Charge: the Electroscope 16-5 Coulomb’s Law16-5 Coulomb’s Law 16-6 Solving Problems Involving Coulomb’s Law and Vectors16-6 Solving Problems Involving Coulomb’s Law and Vectors 16-7 The Electric Field16-7 The Electric Field 16-8 Field lines16-8 Field lines 16-9 Electric Fields and Conductors16-9 Electric Fields and Conductors 16-10 Electric Forces in Molecular Biology (DNA)16-10 Electric Forces in Molecular Biology (DNA)

3. Static Electricity Static Electricity = ? Electric charge = ? TypesTypes InteractionsInteractions Giving an object a net electric chargeGiving an object a net electric charge

4. Static Electricity Law of conservation of electric charge—the net amount of electric charge produced in any process is zero This means = ?This means = ?

5. Electric Charge in the Atom So what are the electric charges in an atom?So what are the electric charges in an atom? What happens if we “charge” an atom?What happens if we “charge” an atom? What is a polar molecule?What is a polar molecule?

6. Insulators and Conductors What are insulators and conductors?What are insulators and conductors? What are examples of insulators and conductors?What are examples of insulators and conductors? Can you charge insulators and/or conductors?Can you charge insulators and/or conductors? –Explain how. What is a semiconductor?What is a semiconductor?

7. Induced Charge: the Electroscope What is an electroscope?What is an electroscope? Can you use an electroscope to find the type of charge on an object?Can you use an electroscope to find the type of charge on an object?

8. Induced Charge: the Electroscope How do you charge an electroscope by conduction?How do you charge an electroscope by conduction? What charge does it get?What charge does it get?

9. Induced Charge: the Electroscope How do you charge an electroscope by induction?How do you charge an electroscope by induction?

10. Induced Charge: the Electroscope How do you charge an electroscope by induction?How do you charge an electroscope by induction? What is grounding?What is grounding? What charge does it get?What charge does it get?

11. Coulomb’s Law F = (kQ 1 Q 2 )/r 2 Where:Where: –F = force between two charged objects (1 & 2) –k = Coulomb's constant (9 x 10 9 N*m 2 /C 2 ) –Q = net charges on objects (Coulomb) 1 electron has the charge of 1.6 x 10 -19 C1 electron has the charge of 1.6 x 10 -19 C –r = distance between objects

12. Coulomb’s Law F = (kQ 1 Q 2 )/r 2 k can be represented byk can be represented by k = 1/(4  0 ) Where  0 = permittivity of free spaceWhere  0 = permittivity of free space –8.85 x 10 -12 C 2 /N*m 2 You will see  0 again laterYou will see  0 again later

13. Coulomb’s Law F = (kQ 1 Q 2 )/r 2 What is the relationship between F, Q’s and r?What is the relationship between F, Q’s and r?

14. Coulomb’s Law F = (kQ 1 Q 2 )/r 2 If the force is between two objects with the same charge the force is repulsive and positiveIf the force is between two objects with the same charge the force is repulsive and positive If the force is between two objects with the opposite charges the force is attractive and negativeIf the force is between two objects with the opposite charges the force is attractive and negative

15. Solving Problems Involving Coulomb’s Law and Vectors The net force acting on an object is the sum of all the forces acting on itThe net force acting on an object is the sum of all the forces acting on it For charged objects, these forces can be calculated using Coulomb’s Law and remembering that force vectors have directionFor charged objects, these forces can be calculated using Coulomb’s Law and remembering that force vectors have direction It is usually better to ignore signs and just deal with direction of force when looking at net force acting on an objectIt is usually better to ignore signs and just deal with direction of force when looking at net force acting on an object

16. Solving Problems Involving Coulomb’s Law and Vectors Example Three charged particles Q 1, Q 2, and Q 3 are arranged in a straight line. They have charges of –8.0  C, 3.0  C and – 4.0  C respectively. Q 1 is 0.3 m from Q 2 and 0.5 m from Q 3. Find the net force on Q 3Three charged particles Q 1, Q 2, and Q 3 are arranged in a straight line. They have charges of –8.0  C, 3.0  C and – 4.0  C respectively. Q 1 is 0.3 m from Q 2 and 0.5 m from Q 3. Find the net force on Q 3Answer 1.5 N toward Q 11.5 N toward Q 1

17. Solving Problems Involving Coulomb’s Law and Vectors Example Three charged particles Q 1, Q 2, and Q 3 are arranged where Q 1 is 52 cm east of Q 2 and Q 3 is 30 cm north of Q 2 They have charges of –86.0  C, 50.0  C and 65.0  C respectively. Find the net force on Q 3Three charged particles Q 1, Q 2, and Q 3 are arranged where Q 1 is 52 cm east of Q 2 and Q 3 is 30 cm north of Q 2 They have charges of –86.0  C, 50.0  C and 65.0  C respectively. Find the net force on Q 3Answer 282.36 N at 64.6° north of east or 25.4° east of north282.36 N at 64.6° north of east or 25.4° east of north

18. The Electric Field Electric field—property of all charged objects the vector sum of the force exerted on a test charge when it is by charged object divided by the charge on the test chargethe vector sum of the force exerted on a test charge when it is by charged object divided by the charge on the test charge Test charge must be ______ and _______. Why?

19. The Electric Field Electric field E = F/q' Why is the electric field not just determined by the force on the test charge?Why is the electric field not just determined by the force on the test charge? What is the unit for electric field strength?What is the unit for electric field strength?

20. The Electric Field Electric field E = F/q' So…F = Eq' So…F = kQq‘/r 2 = Eq' So…E = kQ/r 2 for an electric field generated by charge Q

21. The Electric Field Electric field When the electric field is due to more than one charge, the total field at any point is the vector sum of the individual fields (superposition principle) E = E 1 + E 2 + …..

22. Field Lines Electric field How do you diagram electric field?How do you diagram electric field? –Positive charge How do the lines tell an electric field’s magnitude and direction?How do the lines tell an electric field’s magnitude and direction?

23. Field Lines Electric field How do you diagram electric field?How do you diagram electric field? –Negative charge

24. Field Lines Electric field How do you diagram electric field?How do you diagram electric field? –Two negative charges

25. Field Lines Electric field How do you diagram electric field?How do you diagram electric field? –Two positive charges

26. Field Lines Electric field How do you diagram electric field?How do you diagram electric field? –One negative and one positive charge

27. Field Lines Electric field How do you diagram electric field?How do you diagram electric field? –Between two parallel plates of opposite charge

28. Electric Fields and Conductors The electric field inside a good conductor is zero in the static situation (when charges are at rest)The electric field inside a good conductor is zero in the static situation (when charges are at rest) Any net charge on a good conductor distributes itself on the surfaceAny net charge on a good conductor distributes itself on the surface The direction of the electric field is perpendicular to the surface of the conductorThe direction of the electric field is perpendicular to the surface of the conductor

29. Electric Fields and Conductors For a hollow sphere with a charge in it; there is an electric field due to net charges on inside and outside surface so there is an electric field inside and outside but not within the metalFor a hollow sphere with a charge in it; there is an electric field due to net charges on inside and outside surface so there is an electric field inside and outside but not within the metal

30. Electric Fields and Conductors For a hollow box inside an electric field; there is no electric field because of the accumulation of charges along its surface (safety in a car)For a hollow box inside an electric field; there is no electric field because of the accumulation of charges along its surface (safety in a car)

31. Electric Forces in Molecular Biology (DNA) What are the four bases in DNA?What are the four bases in DNA? –Thymine, cytosine, adenine, and guanine How do they match up?How do they match up? –Thymine and adenine –Cytosine and guanine What holds the two DNA strands together?What holds the two DNA strands together? –Hydrogen bonds