Física y química 3º E.S.O.

1. Física y química 3º E.S.O. Unit 5: Electricity and magnetism U_5_2_II_Methods of charging at distance U.5_2 d1

2. 5.2.5.3. Methods of Charging (at distance, by induction) At distance In contact By friction By conduction By induction U.5_2 d41

3. 5.2.5.3. Methods of Charging (at distance, by induction) a.- Induced polarization of a conductor. Electric dipole If a positively charged glass rod is brought near the left side of a conducting sphere, it attracts the negative charges, leaving the other side of the sphere positively charged. The result is the formation of what is called an electric dipole, from a Latin phrase meaning “two ends.” U.5_2 d42

4. 5.2.5.3. Methods of Charging (at distance, by induction) a.- Induced polarization of a conductor. Electric dipole When a negatively charged rod is brought near a metal sphere without touching it, the electrons of the metal sphere are repelled. Then some of the positive and negative charges in the sphere are separated. U.5_2 d43

5. 5.2.5.3. Methods of Charging (at distance, by induction) a.1. Charging a conductor by induction using a ground connection (first example). U.5_2 d44

6. 5.2.5.3. Methods of Charging (at distance, by induction) a.1. Charging a conductor by induction using a ground connection (first example). It is also possible to charge a conductor in a way that does not involve contact U.5_2 d45

7. 5.2.5.3. Methods of Charging (at distance, by induction) a.1. Charging a conductor by induction using a ground connection (first example). (b) A negatively charged rod is brought near a metal sphere without touching it. In the sphere, the free electrons closest to the rod move to the other side and some of the positive and negative charges in the sphere are separated. U.5_2 d46

8. 5.2.5.3. Methods of Charging (at distance, by induction) a.1. Charging a conductor by induction using a ground connection (first example). (c) Under most conditions the earth is a good electrical conductor. So when a metal wire is attached between the sphere and the ground, some of the free electrons leave the sphere and distribute themselves over the much larger earth. U.5_2 d47

9. 5.2.5.3. Methods of Charging (at distance, by induction) a.1. Charging a conductor by induction using a ground connection (first example). (d) The result is that the sphere acquires a positive net charge U.5_2 d48

10. 5.2.5.3. Methods of Charging (at distance, by induction) a.2. Charging a conductor by induction using a ground connection (second example). (a) A positively charged rod is brought near a neutral metal sphere, polarizing it. U.5_2 d49

11. 5.2.5.3. Methods of Charging (at distance, by induction) a.2. Charging a conductor by induction using a ground connection (second example). (b) The sphere is grounded, allowing the electrons from Earth to be attracted and to enter inside the sphere (a) A positively charged rod is brought near a neutral metal sphere, polarizing it. U.5_2 d50

12. 5.2.5.3. Methods of Charging (at distance, by induction) a.2. Charging a conductor by induction using a ground connection (second example). (b) The sphere is grounded, allowing the electrons from Earth to be attracted and to enter inside the sphere (a) A positively charged rod is brought near a neutral metal sphere, polarizing it. (c) The ground connection is broken. U.5_2 d51

13. 5.2.5.3. Methods of Charging (at distance, by induction) a.2. Charging a conductor by induction using a ground connection (second example). (b) The sphere is grounded, allowing the electrons from Earth to be attracted and to enter inside the sphere (a) A positively charged rod is brought near a neutral metal sphere, polarizing it. (c) The ground connection is broken. (d) The positive rod is removed, leaving the sphere with an induced negative charge. U.5_2 d52

14. 5.2.5.3. Methods of Charging (at distance, by induction) a.3. Charging conductors by induction without a ground connection. (a) We see two neutral metal spheres in contact with one another but insulated from the rest of the world. U.5_2 d53

15. 5.2.5.3. Methods of Charging (at distance, by induction) a.3. Charging conductors by induction without a ground connection. (a) We see two neutral metal spheres in contact with one another but insulated from the rest of the world. (b) A positively charged rod is brought near one of them, attracting negative charge to that side, leaving the other sphere positively charged. U.5_2 d54

16. 5.2.5.3. Methods of Charging (at distance, by induction) a.3. Charging conductors by induction without a ground connection. (a) We see two neutral metal spheres in contact with one another but insulated from the rest of the world. (b) A positively charged rod is brought near one of them, attracting negative charge to that side, leaving the other sphere positively charged. (c) The spheres are separated before the rod is removed, thus separating negative and positive charges. U.5_2 d55

17. 5.2.5.3. Methods of Charging (at distance, by induction) a.3. Charging conductors by induction without a ground connection. (a) We see two neutral metal spheres in contact with one another but insulated from the rest of the world. (b) A positively charged rod is brought near one of them, attracting negative charge to that side, leaving the other sphere positively charged. (c) The spheres are separated before the rod is removed, thus separating negative and positive charges. (d) The spheres retain net charges without having been touched by a charged object. U.5_2 d56

18. 5.2.5.3. Methods of Charging (at distance, by induction) b. Induced polarization of an insulator. In an unpolarized atom or molecule, a negatively charged, electrons are evenly distributed around the positively charged centers U.5_2 d71

19. 5.2.5.3. Methods of Charging (at distance, by induction) b. Induced polarization of an insulator. Both positive and negative objects attract a neutral object by polarizing its atoms or molecules. A polarized atom or molecule has an excess of negative charge at one side, so that the other side has an excess of positive charge. However, the entire system remains electrically neutral. U.5_2 d58

20. 5.2.5.3. Methods of Charging (at distance, by induction) b. Induced polarization of an insulator. Both positive and negative objects attract a neutral object by polarizing its atoms or molecules. (a) A positive object brought near a neutral insulator polarizes its molecules. (b) A negative object produces the opposite polarization. (c) The same effect occurs for a conductor, but electrons can move U.5_2 d59

21. 5.2.5.3. Methods of Charging (at distance, by induction) b.1. Charging insulators by induction If a negatively charged rod is brought near an insulating material like plastic, the positive and negative charges in the molecules of the insulating material separate slightly, but electrons cannot move freely. The negative charges are “pushed” away from the negative rod. Although no net charge is created, the surface of the plastic acquires a slight induced positive charge and is attracted to the negative rod. U.5_2 d60

22. 5.2.5.3. Methods of Charging (at distance, by induction) b.1. Charging insulators by induction U.5_2 d61

23. 5.2.6. Static electricity and static discharge a. Electrostatic discharge of a person The number of positive and negative charges in our boy is the same, so that we are neutral. When we walk on certain floors, the friction between the soles of our shoes and the floor generates a static charge. When you walk across a carpet, electrons move from the carpet to your body, giving you a negative charge. U.5_2 d62

24. 5.2.6. Static electricity and static discharge These electrons (this static charge) stay in place, on the surface of our body, until we touch someone or something. Then the electrons jump or discharge to that person or object. This release of electricity is called an electrostatic discharge U.5_2 d63

25. 5.2.6. Static electricity and static discharge b. Lighting The number of positive charges in a cloud is the same as the number of negative charges, so a cloud is neutral. It is the same for the ground. U.5_2 d64

26. 5.2.6. Static electricity and static discharge b. Lighting Let´s take a look at what is actually happening inside of the cloud U.5_2 d65

27. 5.2.6. Static electricity and static discharge b. Lighting Rain particles in a cloud are more dense than snow particles U.5_2 d66

28. 5.2.6. Static electricity and static discharge b. Lighting As the particles cool down and freeze, they become less dense so the snowflakes or the ice are going up to the top of the cloud. U.5_2 d67

29. 5.2.6. Static electricity and static discharge b. Lighting The heavier raindrops fall towards the bottom of the cloud and to the ground. U.5_2 d68

30. 5.2.6. Static electricity and static discharge b. Lighting Sometimes they collide to each other and friction occurs. U.5_2 d69

31. 5.2.6. Static electricity and static discharge b. Lighting As we know, friction is a method of charging. Snowflakes get a positive charge while raindrops get a negative one. U.5_2 d70

32. 5.2.6. Static electricity and static discharge b. Lighting Then as the snowflakes are going up to the top of the cloud, they take a positive charge. U.5_2 d71

33. 5.2.6. Static electricity and static discharge b. Lighting As the raindrops go down, they take a negative charge. U.5_2 d72

34. 5.2.6. Static electricity and static discharge b. Lighting https://www.youtube.com/watch?v=9HS08L1EIjQ Particles become charged through friction when they collide. More dense rain particles become negatively charged and less dense snow particles become positively charged. This creates a separation of charges in the cloud. The ground at this point is remaining neutral. U.5_2 d73

35. 5.2.6. Static electricity and static discharge b. Lighting Separation of charges in the cloud. The ground is still neutral. U.5_2 d74

36. 5.2.6. Static electricity and static discharge If the process continues there will be a very important separation of charges in the cloud. U.5_2 d75

37. 5.2.6. Static electricity and static discharge If the process continues there will be a very important separation of charges in the cloud. Will the top of the ground remain neutral now?. U.5_2 d76

38. 5.2.6. Static electricity and static discharge The negative charges in the bottom of the cloud repell the electrons in the ground… Will the top of the ground remain neutral now?. U.5_2 d77

39. 5.2.6. Static electricity and static discharge The negative charges in the bottom of the cloud repel the electrons in the ground… and, by induction, as they become repelled, the very top of the ground is left with its positive charges. If the process continues there will be a very important separation of charges in the cloud. Will the top of the ground remain neutral now?. U.5_2 d78

40. 5.2.6. Static electricity and static discharge As a result there are a lot of positive charges in the top of the cloud, a lot of negative charges in the bottom of the cloud… ...and the ground is positively charged U.5_2 d79

41. 5.2.6. Static electricity and static discharge The negative charges in the bottom of the cloud are attracted by the positive charges on the top of the ground ... … so that, suddenly, the electrons from the cloud jump throught lighting to the ground U.5_2 d80

42. 5.2.6. Static electricity and static discharge U.5_2 d81

43. 5.2.6. Static electricity and static discharge c. How a lighting rod works U.5_2 d82

44. 5.2.6. Static electricity and static discharge Many people believe that lightning rods "attract" lightning, but a lightning rod only provides a low-resistance path to ground. The lightning rod is an excellent conductor that allows the current of electrons to flow to ground without causing any heat damage. If the strike contacts a material that is not a good conductor, the material will suffer massive heat damage U.5_2 d83

45. U.5_2 d84