1. Unit 5: Electricity and magnetism
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)
In contact
At distance
By friction
By conduction
By induction
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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.
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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).
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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.
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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).
(a) A positively charged rod is brought near a neutral metal sphere, polarizing it.
(b) The sphere is grounded, allowing the electrons from Earth to be attracted and to enter inside the sphere
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).
(a) A positively charged rod is brought near a neutral metal sphere, polarizing it.
(b) The sphere is grounded, allowing the electrons from Earth to be attracted and to enter inside the sphere
(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).
(a) A positively charged rod is brought near a neutral metal sphere, polarizing it.
(b) The sphere is grounded, allowing the electrons from Earth to be attracted and to enter inside the sphere
(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.
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22. 5.2.5.3. Methods of Charging (at distance, by induction)
b.1. Charging insulators by induction
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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.
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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.
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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
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27. 5.2.6. Static electricity and static discharge
b. Lighting
Rain particles in a cloud are more dense than snow particles
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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.
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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.
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30. 5.2.6. Static electricity and static discharge
b. Lighting
Sometimes they collide to each other and friction occurs.
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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.
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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.
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33. 5.2.6. Static electricity and static discharge
b. Lighting
As the raindrops go down, they take a negative charge.
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34. 5.2.6. Static electricity and static discharge
b. Lighting
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.
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35. 5.2.6. Static electricity and static discharge
b. Lighting
Separation of charges in the cloud.
The ground is still neutral.
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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.
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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?.
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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?.
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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
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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
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42. 5.2.6. Static electricity and static discharge
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43. 5.2.6. Static electricity and static discharge
c. How a lighting rod works
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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.
If the strike contacts a material that is not a good conductor, the material will suffer massive heat damage
The lightning rod is an excellent conductor that allows the current of electrons to flow to ground without causing any heat damage.
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45. U.5_2 d84