8th Grade. Slide 1 / 134. Slide 2 / 134. Slide 3 / 134. Types of Interactions. Table of Contents

Transcription

1 Slide 1 / 134 Slide 2 / 134 8th Grade Types of Interactions Table of ontents Slide 3 / 134 lick on the topic to go to that section Transfer of Forces Interactions between Electric harges Electric Forces Electric Fields Magnetism Magnetic Fields Electromagnetic Interactions

2 Slide 4 / 134 The Transfer of Forces Return to Table of ontents Forces in the Universe Slide 5 / 134 Let's review Newton's Laws of Motion. With a partner, describe Newton's Three Laws of Motion. Record your answers on the next slide. Review: Newton's Laws Slide 6 / 134 First Law: Second Law: Third Law:

3 QUESTION Slide 7 / 134 What are some ways we can apply a force to an object? Work in your group to brainstorm some ways that forces can be applied to an object.? Write them down on your notes and be prepared to share your groups ideas. Forces cting on Objects Slide 8 / 134 Some forces can be transferred by actually touching an object. Other forces are able to work without touching an object, even through empty space! Let's lassify the Forces into 2 ategories Forces that act by Direct ontact (by touching) Forces that ct without Direct ontact (without touching) Slide 9 / 134

4 Forces cting Over a Distance Slide 10 / 134 The forces that act over a distance are going to be exerted over what we call a "field". These forces are called field forces. Definition of field (from Physics): region of space characterized by a physical property, such as gravitational or electromagnetic force or fluid pressure, having a determinable value at every point in the region. 1 Which of the following is NOT an example of a force being exerted through a field? Slide 11 / 134 D Gravity pulling on a falling apple man pushing a car magnet attracting a steel ball n electrically charged balloon pushing on another balloon from across the room 1 Which of the following is NOT an example of a force being exerted through a field? Slide 11 (nswer) / 134 D Gravity pulling on a falling apple nswer man pushing a car magnet attracting a steel ball n electrically charged balloon pushing on another balloon from across [This the object room is a pull tab]

5 2 balanced force acting on an object will cause it to accelerate (change velocity). Slide 12 / 134 True False 2 balanced force acting on an object will cause it to accelerate (change velocity). Slide 12 (nswer) / 134 True False nswer False [This object is a pull tab] Force cting Through Fields Slide 13 / 134 Here's one example of a force acting through a field over a distance without touching. Is the red ball affected by Earth? What force is at work in this diagram?

6 Newton's Universal Law of Gravitation Slide 14 / 134 ny two objects with mass will exert a force of attraction to each other even over vast distances. This force acts on both objects, pulling them towards each other. teacher can even exert a force of gravitation on their students! lick here to see a video on the Law of Gravitation 3 What factors affect the force of gravity between two objects? (hoose all that apply.) Slide 15 / 134 mass of the objects weight of the objects distance between the objects D force of the objects 3 What factors affect the force of gravity between two objects? (hoose all that apply.) Slide 15 (nswer) / 134 mass of the objects weight of the objects nswer distance between the objects & D force of the objects

7 4 What happens to the force of gravity between two objects as they move apart? Increases due to distance Slide 16 / 134 Decreases due to distance Nothing because the masses dont change D impossible to tell without knowing what the objects are 4 What happens to the force of gravity between two objects as they move apart? Increases due to distance Slide 16 (nswer) / 134 Decreases due to distance nswer Nothing because the masses dont change D impossible to tell without knowing what the objects are 5 When talking about the gravity between you and Earth, Earth has a larger force acting on it than you do. Slide 17 / 134 True False

8 5 When talking about the gravity between you and Earth, Earth has a larger force acting on it than you do. Slide 17 (nswer) / 134 True False nswer False Mathematical Relationships in Physics Slide 18 / 134 efore we discuss the law of gravitation in great detail, it is important to understand basic mathematical relationships used in science. We can "read" equations to determine how the variables in the equations affect each other. Mathematical relationships tend to be classified into two main categories. Directly Proportional & Inversely Proportional Directly Proportional What is meant by the term "directly proportional"? Slide 19 / 134 In an equation, as one amount increases, another amount increases at the same rate. Example: child is paid $1.00 per paper delivered on his/her newspaper route. If they deliver more papers, they earn more money. This works in reverse as well, if the child's bicycle chain breaks and they deliver less papers, then he/she makes less money.

9 Inversely Proportional Slide 20 / 134 In an equation, as one amount increases, another amount decreases at the same rate. Example: s the paperboy increases his/her speed of delivery, the time it takes to complete his/her route decreases! nd as the paperboy decreases his/her speed of delivery, the time it takes to complete his/her route increases! 6 person increases their distance away from a light bulb, the observed brightness decreases. What is the mathematical relationship observed during this event? Slide 21 / 134 Inversely Proportional Directly Proportional 6 person increases their distance away from a light bulb, the observed brightness decreases. What is the mathematical relationship observed during this event? Slide 21 (nswer) / 134 nswer Inversely Proportional Directly Proportional [This object is a pull tab]

10 7 college student increases her time studying. Her test grades also increase. What is the relationship between time studying and earned grades? Slide 22 / 134 Inversely Proportional Directly Proportional 7 college student increases her time studying. Her test grades also increase. What is the relationship between time studying and earned grades? Slide 22 (nswer) / 134 nswer Inversely Proportional Directly Proportional [This object is a pull tab] 8 s the voltage in a circuit is increased, the amount of electrical current is also increased. What is the mathematical relationship observed during this event? Slide 23 / 134 Inversely Proportional Directly Proportional

11 8 s the voltage in a circuit is increased, the amount of electrical current is also increased. What is the mathematical relationship observed during this event? Slide 23 (nswer) / 134 Inversely Proportional nswer Directly Proportional [This object is a pull tab] Slide 24 / s the resistance in a circuit is increased, the amount of electrical current is decreased. What is the mathematical relationship observed during this event? Inversely Proportional Directly Proportional Slide 24 (nswer) / s the resistance in a circuit is increased, the amount of electrical current is decreased. What is the mathematical relationship observed during this event? nswer Inversely Proportional Directly Proportional [This object is a pull tab]

12 10 We know that the force of gravity between two objects increases as the masses get larger. This relationship is proportional. Slide 25 / 134 directly inversely 10 We know that the force of gravity between two objects increases as the masses get larger. This relationship is proportional. Slide 25 (nswer) / 134 directly inversely nswer omparing Forces of Gravity Slide 26 / 134 ompare the force of gravity acting on you (your weight) on Earth compared to the moon: Which is larger? WHY?

13 omparing Forces of Gravity Slide 27 / 134 What happens to the force of gravity on an object as we move farther away from a massive object like Earth? With your group, compare the force of gravity (weight of boy) at points,, & and be ready to share. Distance and Forces of Gravity Slide 28 / 134 The force of gravity exerted by an object decreases as it moves away from an object like Earth. s the boy moves away from Earth, his weightwill decrease. 11 s the same boy from the last slide moves farther from Earth, will his mass change? Slide 29 / 134 Yes No

14 11 s the same boy from the last slide moves farther from Earth, will his mass change? Slide 29 (nswer) / 134 Yes No nswer No Why can't we feel the forces of Gravitation acting between two people? Slide 30 / 134 Even though there is always a gravitational force acting between masses, it is only noticeable when the objects' masses are relatively large. If we were to compare our mass to that of a planet, a person's mass is so small that the gravitational force they produce is almost unmeasurable. Small Masses = Small Force of Gravitation 12 The force of gravity as the object's mass increases. Slide 31 / 134 Increases Remains onstant Decreases

15 12 The force of gravity as the object's mass increases. Slide 31 (nswer) / 134 Increases Remains onstant Decreases nswer 13 The force of gravity as the distance between two objects increases. Slide 32 / 134 Increases Remains onstant Decreases 13 The force of gravity as the distance between two objects increases. Slide 32 (nswer) / 134 Increases Remains onstant Decreases nswer

16 Distance and Forces of Gravity Slide 33 / 134 The force of gravity does not decrease at a constant rate as an object moves away from a planet. The Force of Gravity actually decreases exponentially as distance increases! Distance and Forces of Gravity Slide 34 / 134 If we graph the force of gravity (Newtons) vs. distance of separation (m) of an object as it moves away from a planet, this is what we get: Distance and Forces of Gravity Slide 35 / 134 The decrease in the force of gravity does not decrease at a constant rate. If it did the graph would look like this: Note: This graph is not the real pattern we observe in nature.

17 14 Force is proportional to distance. Slide 36 / 134 Directly Indirectly 14 Force is proportional to distance. Slide 36 (nswer) / 134 Directly Indirectly nswer Distance and Forces of Gravity Slide 37 / 134 The true pattern observed by scientists showed that the force of gravity is inversely proportional to distance of separation squared! F = 1 d 2 NOTE: This is almost the same as regular inversely proportional, but the force decreases much more as distance increases because it is squared.

18 Putting it all together Slide 38 / 134 Putting all these ideas together, fill in the blanks below with the correct mathematical relationships. The Gravitational Force between 2 masses is to the product of the masses and to the distance of the separation squared d Gravitational Field Lines Slide 39 / 134 We can represent the gravitational field around a mass with lines of force. The lines point inward and then spread apart as we move away from Earth. Why? ome up with an idea with your table. 15 The force of gravity decreases at a constant rate as we move away from a planet like Jupiter. Slide 40 / 134 True False

19 15 The force of gravity decreases at a constant rate as we move away from a planet like Jupiter. Slide 40 (nswer) / 134 True False nswer False 16 s we move away from the Sun, the force of gravity gets weaker by an inverse of the: Slide 41 / 134 distance cubed distance distance squared 16 s we move away from the Sun, the force of gravity gets weaker by an inverse of the: Slide 41 (nswer) / 134 distance cubed distance nswer distance squared

20 Slide 42 / 134 Interactions etween Electric harges Return to Table of ontents What is Electric harge? Slide 43 / 134 Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter. There are two types of electric charges: positive and negative Positive or Negative? Slide 44 / 134 Do you know who coined the terms positive and negative charge? Remember all atoms are composed of 3 basic subatomic particles. What were those particles?

21 Positive harge Slide 45 / 134 Objects that are positively charged are out of balance, meaning they have more protons than electrons Since the box has more protons (+) than electrons(-), it is POSITIVELY HRGED. Negative harge Slide 46 / 134 Objects that are negatively charged are out of balance, meaning they have more electrons than protons Since the box has more electrons(-) than protons (+), it is NEGTIVELY HRGED. hemistry onnection Slide 47 / 134 lick on the simulation image to the left. Hit the green plus sign on NET HRGE to show the overall charge on the atom. What gives an atom a net: a) positive charge? b) negative charge? c) neutral charge? Note the effect on net charge when you: dd protons dd electrons dd neutrons

22 hemistry onnection Slide 47 (nswer) / 134 lick on the simulation image to the left. What gives an atom a net: a) positive charge? b) negative charge? c) neutral charge? Teacher Notes Hit the green plus sign on NET HRGE to show the overall charge hoose on the the atom. "run in HTML 5" option. Note the effect on net charge when you: dd protons dd electrons dd neutrons [This object is a teacher notes pull tab] 17 What makes an object exhibit an overall positive charge? Slide 48 / 134 D more protons in the object more electrons than protons in the object more protons than electrons in the object less electrons in the object 17 What makes an object exhibit an overall positive charge? Slide 48 (nswer) / 134 more protons in the object nswer more electrons than protons in the object more protons than electrons in the object D less electrons in the object

23 18 What makes an object exhibit an overall negative charge? Slide 49 / 134 D equal protons and electrons in the object more electrons than protons in the object more protons than electrons in the object less electrons in the object 18 What makes an object exhibit an overall negative charge? Slide 49 (nswer) / 134 D equal protons and electrons in the object nswer more electrons than protons in the object more protons than electrons in the object less electrons in the object 19 What makes an object exhibit an overall neutral charge? Slide 50 / 134 D equal protons and electrons in the object more electrons than protons in the object more protons than electrons in the object less electrons in the object

24 19 What makes an object exhibit an overall neutral charge? Slide 50 (nswer) / 134 D equal protons and electrons in the object nswer more electrons than protons in the object more protons than electrons in the object less electrons in the object Slide 51 / 134 Electric Forces Return to Table of ontents Forces etween harged Objects Slide 52 / 134 There is one very common way we can see forces between charged objects. You can see it in the picture of the boy below. You might also experience it when you take clothes out of a dryer. What is it? lick here to launch a simulation to explore charging and forces between charges

25 oulomb's Law Slide 53 / 134 In the activity where you had a balloon and a sweater, what happened when you rubbed the balloon on the sweater and then let it go? Just like we saw with masses, forces are exerted between charges! This is called oulomb's Law! 20 Opposite charges repel. Slide 54 / 134 True False 20 Opposite charges repel. Slide 54 (nswer) / 134 True False nswer False

26 21 n electron and a proton are attracted to each other. True Slide 55 / 134 False 21 n electron and a proton are attracted to each other. True Slide 55 (nswer) / 134 False nswer True Electrostatic Force Slide 56 / 134 The interaction between charged objects is a non-contact force that acts over some distance of separation. We call this an electrostatic force. Unlike harges ttract! Opposite harges Repel lick here to see a video on Fun with Static Electricity

27 Electrostatic Force Slide 57 / 134 There are 2 main factors which play into electrostatic forces. 1) harge of the Objects 2) Distance between the 2 objects What other force does this remind you of? Forces between like charges Slide 58 / s the amount of charge increases, what happens to the magnitude (strength) of the force? Electrostatic Force Slide 59 / 134 We observe that the force of repulsion doubles when one of the charge doubles

28 22 Electrostatic force is proportional to the amount of charge present. Slide 60 / 134 directly inversely 22 Electrostatic force is proportional to the amount of charge present. Slide 60 (nswer) / 134 directly inversely nswer Electrostatic Force Slide 61 / 134 The Electrostatic Force direction between 2 charged objects is proportional to the product of their charges. harge harge 1 2 Sign of Product Type of force felt Repulsion Repulsion ttraction

29 Discussion Question Slide 62 / 134 What do you think happens to the force between charges when we move them father apart? Talk about this at your table. d + + s the charges move farther apart, the force between them is decreased. Slide for the answer! Electrostatic Force Slide 63 / 134 Force between charges reduces as the charges move apart. Does this graph look familiar? Putting it all together Slide 64 / 134 The Electric Force between 2 charges is directly proportional to the amount of charge! It also decreases in strength as the charges move farther apart.

30 23 s the amount of charge increases, the force between the charges. Slide 65 / 134 decreases stay the same increases 23 s the amount of charge increases, the force between the charges. Slide 65 (nswer) / 134 decreases stay the same increases nswer 24 s the amount of distance between charges increases, the force between the charges. Slide 66 / 134 decreases stay the same increases

31 24 s the amount of distance between charges increases, the force between the charges. Slide 66 (nswer) / 134 decreases stay the same increases nswer How is oulomb's Law (forces between charges) similar/different to Newton's Law of Gravitation (forces between masses)? Slide 67 / 134 Similarities Differences nswer Slide 68 / 134 Electric Fields Return to Table of ontents

32 Electric Field Diagrams Slide 69 / 134 These forces can be visualized by drawing lines that represent the forces acting between charges. We will call these electric field diagrams. Five Rules for Electric Field Lines Slide 70 / 134 1) Lines exit positive charges. 2) Lines enter negative charges. 3) Lines don't exist around neutral charges. 4) Lines never cross! 5) Lines that are close together represent stronger forces. Field lines between like charges Slide 71 / 134 oth diagrams help us visualize repulsive forces. Do you see how the lines look like they are pushing apart at their closest points?

33 Field Lines between unlike charges Slide 72 / 134 This diagram indicates electrostatic attraction. The field lines exit the positive charge and enter the negative charge. Unlike the field lines between like charges, these lines look like they are pulling together. Two Oppositely harged Metal Plates Slide 73 / 134 Look at the diagram to the right. What can be said about the spacing and direction of the field lines between the plates? What does this mean? Two Oppositely harged Metal Plates Slide 73 (nswer) / 134 Look at the diagram to the right. What can be said about The the spacing of the field lines spacing and direction of the are field uniform. Therefore, the lines between the plates? field strength is the same at all points between the What does this mean? charged plates. nswer

34 25 Electric field lines exit positive charges and enter negative charges. Slide 74 / 134 True False 25 Electric field lines exit positive charges and enter negative charges. Slide 74 (nswer) / 134 True False nswer True 26 The electric field strength between 2 parallel oppositely charged plates: Slide 75 / 134 Increases as you move towards the postive plate decreases as you move toward the negative plate remains constant at all points between the plates.

35 26 The electric field strength between 2 parallel oppositely charged plates: Slide 75 (nswer) / 134 Increases as you move towards the postive plate nswer decreases as you move toward the negative plate remains constant at all points between the plates. Newton and oulomb omparison Slide 76 / 134 If they are used for both laws place the term on the line. Newton's Law oulomb's Law ttraction Mass Repulsion harge Slide 77 / 134 Magnetism Return to Table of ontents

36 The Discovery of Magnetism Slide 78 / 134 The most popular legend accounting for the discovery of magnets is that of an elderly retan shepherd named Magnes. Legend has it that Magnes was herding his sheep in an area of Northern Greece called Magnesia, about 4,000 years ago. Suddenly both the nails in his shoes and the metal tip of his staff, became firmly stuck to the large black rock on which he was standing. What do you think was special about that rock? Magnetic Rocks? Slide 79 / 134 To find the source of attraction he dug up the Earth to find lodestones (load = lead or attract). Lodestones contain magnetite, a natural magnetic material Fe 3O 4. This type of rock was subsequently named magnetite, after either Magnesia or Magnes himself. What is Magnetism? Magnetism is a class of physical phenomena that includes forces exerted by magnets on other magnets. Slide 80 / 134 It has its origin in electric currents.

37 27 Magnetism is a force. Slide 81 / 134 contact field neither 27 Magnetism is a force. Slide 81 (nswer) / 134 contact field neither nswer William Gilbert Slide 82 / 134 scientist named William Gilbert is given credit to understanding magnetism. William Gilbert made 2 profound discoveries: Earth was a giant magnet and also that magnets could be produced by beating wrought iron!

38 Magnetic Domains Slide 83 / 134 magnetic domain is a microscopic region within a magnetic material which has uniform magnetization. This means that the individual magnetic regions of the atoms are aligned with one another and they point in the same direction. Non-Magnetized Substances Slide 84 / 134 If the magnetic domains (microscopic magnetic regions) are randomized, the substance will have no overall magnetic properties. Slide 85 / 134 Magnetized Substances If the magnetic domains (microscopic magnetic regions) are aligned, the substance will have overall magnetic properties and act as a magnet.

39 Permanent Magnets Slide 86 / 134 permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic. Ferromagnetic Substances Slide 87 / 134 These include iron, nickel, cobalt, some alloys of rare earth metals, and some naturally occurring minerals such as lodestone. On the periodic table of Elements, these 3 elements are grouped together. Is this just a coincidence? Temporary Magnets Slide 88 / 134 Temporary Magnets simply act like permanent magnets when they are within a strong magnetic field. Unlike permanent magnets however, they loose their magnetism when the field disappears. Paperclips, iron nails and other similar items are examples of temporary magnets.

40 Magnetizing an Iron Nail Slide 89 / 134 Un-Magnetized Iron- Domains are random Magnetized Iron- Domains are aligned Electromagnets Slide 90 / 134 Electromagnets have a soft metal core made into a magnet by the passage of electric current through a coil surrounding it. Unlike permanent magnets however, they lose their magnetism when the current disappears. 28 Michael Faraday discovered Earth was a giant magnet. Slide 91 / 134 True False

41 28 Michael Faraday discovered Earth was a giant magnet. Slide 91 (nswer) / 134 True False nswer False 29 Microscopic regions inside iron are called: Slide 92 / 134 magnetic crystals magnetic domains magnetic atoms 29 Microscopic regions inside iron are called: Slide 92 (nswer) / 134 magnetic crystals nswer magnetic domains magnetic atoms

42 30 Ferromagnetics substances include: (select all that are ferromagnetic) Slide 93 / 134 D iron aluminum nickel cobalt 30 Ferromagnetics substances include: (select all that are ferromagnetic) Slide 93 (nswer) / 134 iron aluminum D nickel cobalt nswer,, D 31 n electromagnet produces a magnetic field when current stops flowing through it. Slide 94 / 134 True False

43 31 n electromagnet produces a magnetic field when current stops flowing through it. Slide 94 (nswer) / 134 True False nswer False 32 Soft Iron is an example of. Slide 95 / 134 D an electromagnet a temporary magnet a permanant magnet a superconductor 32 Soft Iron is an example of. Slide 95 (nswer) / 134 D an electromagnet a temporary magnet nswer a permanant magnet a superconductor

44 Slide 96 / 134 Magnetic Fields Return to Table of ontents Magnetic Poles Slide 97 / 134 Every magnet has 2 poles - North and South It's similar to the charge being either positive or negative Forces between Magnetic Poles Slide 98 / 134 Opposite magnetic poles attract. Like magnetic poles repel. lick here to launch a video on magnetic levitation

45 The ompass Slide 99 / 134 The compass is an indicator of Earth's magnetic field. compass is just a bar magnet that is free to swing about. The compass needle is attracted to Earth's magnetic poles. Geographic and Magnetic Poles Slide 100 / 134 Earth's Geographic North Pole is actually a Magnetic South Pole! Earth's Geographic South Pole is actually a Magnetic North Pole! compass' true North Pole is attracted to Earth's Geographic North Pole (Magnetic South Pole), and vice versa. Magnetic Field Line Drawings Slide 101 / 134 Forces around magnets can be visualized by "lines of force" These lines indicate the strength of a magnetic field. Where have we seen force lines like this before?

46 3 Magnetic Field Line Rules Slide 102 / 134 Lines exit North Poles and enter South Poles loser lines equal stronger force Field lines never cross! Magnetic Field Drawings Slide 103 / 134 s we move away from a magnetic pole, What happens to the strength of the magnetic field? ompare the spacing of the field lines at vs. What do you notice? Visualizing Magnetic Fields Slide 104 / 134 y sprinkling iron filings around a magnet, we see that they will line up differently depending on the magnetic field of the magnet.

47 33 This photo depicts magnets which could be aligned Slide 105 / 134 North North North South 33 This photo depicts magnets which could be aligned Slide 105 (nswer) / 134 North North North South nswer 34 This photo depicts magnets which could be aligned Slide 106 / 134 North North North South

48 34 This photo depicts magnets which could be aligned Slide 106 (nswer) / 134 North North North South nswer Magnetic Fields Lines Slide 107 / 134 an you visualize the photos you just saw with these drawings? ttractive force between unlike poles Slide 108 / 134 This magnetic field line diagram shows an attractive force between unlike poles.

49 Repulsive force between like poles Slide 109 / 134 This magnetic field line diagram shows a repulsive force between like poles. Test Magnet compass placed into the magnetic field will act as a "test magnet" and swing to line up with the direction of the magnetic field around a magnet Slide 110 / 134 In oxes &, draw a compass that shows the direction of the field around the magnet. 35 Like magnetic poles: Slide 111 / 134 attract repel don't interact

50 35 Like magnetic poles: Slide 111 (nswer) / 134 attract repel don't interact nswer 36 This type of field drawing represents: Slide 112 / 134 attraction repulsion suspension 36 This type of field drawing represents: Slide 112 (nswer) / 134 attraction repulsion suspension nswer

51 37 test compass at will be oriented like: Slide 113 / 134 D 37 test compass at will be oriented like: Slide 113 (nswer) / 134 nswer D 38 test compass at will be oriented: Slide 114 / 134 D

52 38 test compass at will be oriented: Slide 114 (nswer) / 134 nswer D 39 Magnetic Field lines exit from the south pole of a magnet. Slide 115 / 134 True False 39 Magnetic Field lines exit from the south pole of a magnet. Slide 115 (nswer) / 134 True False nswer False

53 40 s distance is increased away from a magnetic field source, the magnetic field intensity will. Slide 116 / 134 Increase Decrease Stay the same 40 s distance is increased away from a magnetic field source, the magnetic field intensity will. Slide 116 (nswer) / 134 Increase Decrease nswer Stay the same Slide 117 / 134 Electromagnetic Interactions Return to Table of ontents

54 Magnetism and Electricity Slide 118 / 134 In 1820, Hans hristian Oersted, a Danish Physicist, demonstrated that magnetism was related to electricity. y bringing a wire carrying an electric current close to a magnetic compass he noticed a deflection of the compass needle. Electrical urrent and Magnetic Fields Slide 119 / 134 n electrical current (moving charge) placed through a wire produces a magnetic field around the wire! In this diagram, the red lines circling the wire are the magnetic field lines! Electrical urrent and Magnetic Fields Slide 120 / 134 The greater the electrical current, the greater the strength of the magnetic field produced. The magnitude of magnetic field produced by a straight current-carrying wire at a given point is: Directly proportional to the current passing in the wire. Inversely proportional to the distance of that point from the wire.

55 Simulating the affect of current on the magnetic field produced around a wire Slide 121 / 134 lick on the picture to the left to launch the simulation. lick Electromagnet on the top. hange # of loops to 1, click show field meter. Vary the voltage to change the amount of current What happens to the field strength as we change current? What happens to the field strength as we move the meter away from the loops? Visualizing Magnetic Fields in the Lab Slide 122 / 134 y sprinkling iron filings around a magnet, we see that they will line up with the magnetic field of the magnet. The Right Hand Rule Grab a wire with your right hand with your thumb pointing in the same direction as the current. I Slide 123 / 134 Your fingers point in the direction of the magnetic field!

56 Visualizing Magnetic Fields Slide 124 / 134 If we look down the wire, from either end, the magnetic field will turn clockwise (W) or counter-clockwise (W) Magnetic Field round a oil Slide 125 / 134 The magnetic field around a coil is similar to the field that we see around a bar magnet. The Left Hand Rule Slide 126 / 134 For a OIL, use the LEFT HND RULE. - When the fingers point in the direction of the current in the loops, your thumb points in the North direction of the magnetic field lick for a video on the Left Hand Rule

57 What happens when we move a bar magnet near a wire/coil? Slide 127 / 134 Let's run a simulation to explore what happens Slide 128 / 134 lick on the image to the left to launch the simulation. Move the bar magnet through the coil. What happens in the coil? Move the coil around the magnet. What happens in the coil? This process of producing electricity from magnetism is called "Induction". Electrical urrent and Magnetic Field Slide 129 / 134 We have seen that moving magnetism can can produce an electrical current in a wire. How might this be put to use in our modern society?

58 Michael Faraday- The Father of Electromagnetism Slide 130 / 134 ritish physicist and chemist, best known for his discoveries of electromagnetic induction and of the laws of electrolysis. His biggest breakthrough in electricity was his invention of the electric motor. lick here to see a video on Michael Faraday's Electromagnetism 41 Moving electricity causes a magnetic field to form. Slide 131 / 134 True False 41 Moving electricity causes a magnetic field to form. Slide 131 (nswer) / 134 True False nswer True

59 42 The rule is the rule that relates the direction of a magnetic field surrounding a wire carrying current. Slide 132 / 134 D left thumb right hand right arm left hand 42 The rule is the rule that relates the direction of a magnetic field surrounding a wire carrying current. Slide 132 (nswer) / 134 left thumb right hand nswer right arm D left hand 43 The father of modern electromagnetic theory is: Slide 133 / 134 D en Franklin Sir Isaac Newton Michael Faraday Richard Feinman

60 43 The father of modern electromagnetic theory is: Slide 133 (nswer) / 134 D en Franklin Sir Isaac Newton nswer Michael Faraday Richard Feinman 44 The rule is used to determine the direction of the magnetic field around a current carrying coil. Slide 134 / 134 D right hand left hand right thumb left thumb 44 The rule is used to determine the direction of the magnetic field around a current carrying coil. Slide 134 (nswer) / 134 right hand left hand right thumb nswer D left thumb