Electricity Grade 9 Science Mr. Frittenburg

1. ElectricityGrade 9 ScienceMr. Frittenburg

2. Montreal Ice Storm 1998 • On the morning of January 6th. 1998, residents of Southern Quebec, Eastern Ontario and the Northern New England States awoke to find themselves in the midst of a severe ice storm, the likes of which had not been witnessed in recent memory. • At the height of the storm in excess of one million households were without electricity. Bridges and roads were closed. • http://archives.cbc.ca/environment/extreme_weather/topics/258/

3. Characteristics of Electricity • Disasters such as ice storms make us realize how much modern societies depend on electricity. Everyone uses it, but how many people know how electricity is generated, how the energy is transmitted through those kilometers of power lines, and how it operates your toaster or your television set? • Understanding electricity is the first step toward proper use and conservation of this very important modern convenience.

4. Static Electricity • A: What causes lightning and why does it strike tall buildings and trees? • B: Why do you sometimes, but not always, get an electric shock from a doorknob? • C: Why do clothes taken from a clothes dryer sometimes cling together? • Think about the above questions, attempt to give a detailed answer on a reflection page to put in your SLLOG. As you study this chapter, return to your SLLOG if you want to change any of your answers.

5. Static Electricity Lightning looks like a giant spark. Is it? What causes a spark or a bolt of lightning? Electricity out of control can cause serious damage. Can we control it? If so, how? What are some other noticeable effects of electrical activity? Perform the Starting Point Activity from page 295 of your text to begin to get an understanding of static electricity.

6. Static Electricity • The shocks you get from walking across a carpet and touching a metal doorknob look like exceedingly small lightning bolts. This is exactly what they are. • In a thunderstorm, water droplets and ice crystals in the clouds are buffeted by the strong winds, colliding and rubbing against each other. When you walk across a room, your shoes or socks rub against the carpet. But why would rubbing create the condition that results in sparks?

7. Static Electricity - Thales lived in Greece about 600 B.C.E. he was the first to record observations about a change in properties of amber when rubbed with fur. • Thales noticed when he rubbed amber with fur, the amber attracted small pieces of straw and wood shavings. • Scientists studied this in detail hundreds of years later discovering that many combinations of materials, when rubbed against each other attract straw, small pieces of paper, and various other objects.

8. Static Electricity • Scientists used the word charged to describe materials that attracted other materials after rubbing. • They said that the materials carried an electric charge. • Since the charges remained stationary on the surface of the charged object, they called it static electricity. • Electrostatics is the science of static electricity. • Materials that do not carry a charge are said to be neutral.

9. Static Electricity • For many materials such as the balloon, the charge stays on the spot where you rub the object. Such materials fit into a class called insulators. • Insulatorsare materials that do not allow charges to move freely on or through the object.

10. Static Electricity • Materials that do allow charges to move freely are classified as conductors. • Most metals are conductors and most non-metals are insulators. • Classify each as either an insulator or conductor: • Aluminum foil • Piece of wood • Paper clip • Eraser • Potato • Gold bracelet

11. Static Electricity Check Your Understanding • What is similar about a spark and a lightning bolt? • How do some charged objects interact with each other differently from the way a charged object interacts with neutral objects? • How do charged conductors and insulators differ from each other? • Explain why a person can get a shock after walking across a carpet. • What do you think would happen if you rubbed two identical objects together? Would they attract each other, repel each other, or neither attract nor repel each other? Why?

12. Static Electricity • As scientists studied more and more types of charged materials, they discovered that all charged objects fit into two categories. • Every charged object in category A repels every other charged object in A, but attracts all charged objects in category B. The same is true of charged objects in category B. • From these studies scientists devised a model that states that there are two types of charges (category A objects carry one type of charge and B objects carry the other). • From this model and data they concluded that “Like charges repel and unlike charges attract”, this is written as the law of attraction and repulsion.

13. Static Electricity • The famous American inventor and politician Benjamin Franklin (1706-1790) named the charges “positive” and “negative” As a scientist he was a major figure in the Enlightenment and `the history of physics for his discoveries and theories regarding electricity. He invented the lightning rod, bifocals, the Franklin stove, a carriage odometer, and a musical instrument

14. Static Electricity • Why do charged objects attract neutral ones?

15. Static Electricity • An electroscope is a device used to detect the presence of a charge.

16. Static Electricity • If you bring a negatively charged rod near, but not touching, the sphere, it will repel the negative charges in the sphere. The negative charges will move down to the leaves. • The sphere will be left with a temporary positive charge. Take away the negative rod and the negative charges on the leaves will go back to the sphere and the leaves will go back to their original position. • This is called charging by induction.

17. Electroscopes

18. Static Electricity Check Your Understanding • Describe the evidence that led the way for scientists to discover the law of attraction and repulsion. • What makes objects neutral? • How can you tell the difference between a positively charged object and a negatively charged object by using an electroscope? • Why must the sphere, rod, and leaves of an electroscope be conductors? • Explain the difference between a negatively charged object and a positively charged object.

19. Static Electricity Answers (Recap) • Many charged items were put into two categories; category A and B. It was found that all charged items in category A repelled each other but were attracted to the charged items in category B. The same was true of items in category B. From this it was derived that like charges repel while unlike charges attract. • Neutral objects have the same number of positive and negative charges. • You can’t, because the metal leaves repel each other in both instances.

20. Static Electricity Answers (Recap) 4. The sphere, rod and leaves of an electroscope must be conductors so it will let a charge move through freely. 5. When an object is rubbed with something (fur) it receives a negative charge (amber). The object used to rub onto an object is left with a positive charge. Negatively charged objects attract positively charged objects, and repel other negatively charged objects. The same is true of positively charged objects.

21. Explaining Static Electricity • In 1600, William Gilbert (1544-1603) proposed that electricity was a fluid, separate from the matter that made up the objects. This “fluid theory” was accepted by scientists for over a hundred years.

22. Explaining Static Electricity • In 1897, when J.J. Thomson (1856-1940) discovered the electron, the fluid theory of electricity had to be discarded.

23. Explaining Static Electricity Review of the Bohr-Rutherford model of the atom

24. Explaining Static Electricity • As you have learned in earlier studies, all matter consists of atoms with positively charged nuclei, containing protons and neutrons, and negatively charged electrons surrounding the nucleus. • Atoms of some elements hold their electrons more loosely than others. Rubbing removes the more loosely held electrons from one material and deposits them on the other. • Positively charged protons remain in place. Materials that gain electrons become negatively charged and those that lose electrons become positively charged.

25. Explaining Static Electricity • Since electrons are the charges that move through solids, a conductor must be a material that holds on to its electrons loosely. • Electrons can jump from one metal atom to the next. However, some metals allow much more free movement of electrons than others. Example: silver is a much better conductor than aluminum because electrons move much more freely within silver than within aluminum. • Insulators are materials that hold their electrons very tightly. As well, some insulators hold their electrons much more tightly than others. • Some materials are in between insulators and conductors, these fair conductors provide a lot of resistance to the movement of electrons (fish swimming upstream).

26. Explaining Static Electricity Question: What causes a spark?

27. Explaining Static Electricity Answer: • When two oppositely charged objects approach each other, but do not touch, if the charge is great enough you will see a spark or an electrical discharge. • If the two objects carry very large, opposite charges, the strength of the interactions can pull apart some of the gas molecules in the air, creating a path of ionized molecules that acts as a conductor. • The excess electrons on the negatively charged object can now move through this new conductor onto the positively charged object. • The electrons move exceedingly fast and collide with more molecules in the air, exciting these molecules so much that they emit light.

28. Explaining Static Electricity • Grounding a conductor means to connect it, through some conducting material, directly to the ground, or Earth. • Although Earth is not an excellent conductor, it is so huge that it can accept or give up many electrons without any significant change in its charge. You could compare the situation to pouring a cup of water into the ocean.

29. Explaining Static Electricity • Grounding of charges can prevent serious accidents. The grounding of electrical appliance around the home also prevents serious, even fatal, shocks. • Electrical wiring in homes, businesses, and industries is always grounded. A common way to ground wiring is to connect a wire to copper water pipes that go deep into the Earth below the building. • The third prong on plugs that fit into wall sockets connects to this ground wire.

30. Explaining Static Electricity Check Your Understanding • What is the fluid theory of electricity? Why did scientists reject the theory? • What type of charge moves through conductors? Explain how it moves? • What does it mean to say that a conductor is grounded? • List two examples of conductors and two examples of insulators. • Use the electron theory to explain how one object can be negatively charged and another can be positively charged. • What must happen to some of the molecules in the air for a spark to occur?

31. Explaining Static Electricity Answers (Recap) • In 1600 William Gilbert stated that electricity was a fluid, separate from the matter that made up objects. • A negative charge (electrons) moves through conductors, the electrons travel through conductors by moving from one atom to the next. • When a conductor is grounded it is connected through a conducting material directly into the ground. • Conductors: copper, aluminum, gold Insulators: rubber, wood, cotton

32. Explaining Static Electricity Answers continued 5. The electron theory of charge states that rubbing removes loosely held electrons from one material and deposits them on the other. Positively charged protons stay in place. Materials that gain electrons become negatively charged and those that lose electrons become positively charged. 6. Before a spark can occur the molecules in air must split apart making an invisible path of positive and negative ions. This path of ionized molecules that forms in the air acts as a conductor waiting for a charge to pass through it (spark).

33. Dangers of Static Electricity • Now that you know a little about static electricity it is time to address the negative impacts it has on our lives, and the hazardous situations it can cause. • We will address the specific danger of what happens if one builds up a static charge around a very combustible material like gasoline. And there is no better place to find gasoline then at a gas station. • http://www.pei.org/Uploads/static.mov • This will be the topic for your next small assignment. Danger At The Pumps

34. Controlling Static Electricity Question: What causes thunder and lightning?

35. Controlling Static Electricity • http://science.howstuffworks.com/lightning.htm

36. Controlling Static Electricity What causes lightning? • Strong winds and collisions of water droplets and ice particles in the clouds strip electrons from some particles and deposit them on others. • For reasons meteorologists don’t quite completely understand, negative charges collect at the bottom of the clouds, where the temperature is above -20ºC. The higher, colder, parts of the clouds are positively charged. • The negative charges on the bottom of the clouds repel electrons on the surface of the Earth, leaving the ground positively charged just below the cloud.

37. Controlling Static Electricity • The strong attraction between the negative cloud and the positive ground pull electrons off atoms and molecules in the air (usually takes place over the highest point on the ground). • Once this chain of ions forms, a gigantic discharge occurs between the cloud and the ground. • So many electrons crash through the air so fast, colliding with other molecules, the air not only lights up, it heats up. • The temperature of the air near a lightning bolt can reach as high as 33 000 ºC. • The heat causes the air to expand rapidly; air molecules colliding with more air molecules as they move around produce a shock wave that we hear as thunder.

38. Controlling Static Electricity • Now that you understand lightning and how it can be so dangerous, can you think of a way to direct this flow of electrons away from buildings and prevent fires? • If you are thinking of a lightning rod you would be correct. • Lightning rods were originally developed by Benjamin Franklin. A lightning rod is very simple -- it's a pointed metal rod attached to the roof of a building. The rod might be an inch (2 cm) in diameter. It connects to a huge piece of copper or aluminum wire that's also an inch or so in diameter. The wire is connected to a conductive grid buried in the ground nearby.

39. Controlling Static Electricity

40. Controlling Static Electricity • A lightning rod is charged by induction, just like the sphere on your electroscope when you brought a negatively charged rod near it. • The positively charged lightning rod is the highest point in an area. It attracts the negative ions that have formed in the air, while the cloud attracts the positive ions. • A chain of ions acts as a conductor providing a path for a lightning bolt. • The electrons (lightning bolt) are then carried around the building and into the ground by a heavy conductor, often made of braided wire. • Since the electrons do not go through the building, they cannot heat it enough to start a fire.