Magnetism

1. Introduction Magnetism What is the mysterious force that enables some materials to attract others? How could pieces of rock attract and repel each other? Prepared By GhulamHussain Rajeev Sharma

2. HistoryAs early as 600 B.C. the Greeks discovered that a certain type of iron ore , later known as Lodestone, or Magnetite was able to attract other small pieces of iron. Also when pivoted and allowed to rotate freely, a piece of Lodestone would come to rest in a North-South position. Because of this property, Lodestone was widely used in navigation. The Lodestone is the rock that displayed natural magnetism.Chemical analysis has shown that Lodestone gets its magnetic properties from the presence of an oxide of iron, Fe3O4 , Known today as magnetic iron ore.

3. CompassA compass is simply a magnet that is allowed to rotate horizontally to point north and south.Early compass makers shaped lodestones so that one end always pointed towards Earth geographic north and the other towards the geographic south. Later on these ends were named as North and South Poles of a Compass.The invention of the compass enabled sailors to leave the coast and venture out into the ocean knowing they could find their way back with the compass. This resulted in the great global explorations of the fifteenth and sixteenth centuries, including the discovery of the “New World”Albert Einstein recalled that, as a child, he had been fascinated by compass

4. Lab. Activity---- Making a magnet Use a magnet to change a steel paper clip into a magnet. Use a compass to test the results. Materials: Steel paper clips, compass, bar magnet • Straighten out the paper clips. Bring the compass close to the paper clip and move it all the way around the paper clip. Note the effect on the compass needle. • Drag the north end of the magnet in a sweeping motion along the paper clip several times. Make sure the sweeping motion is from left to right and that the magnet is lifted high above the paper clip when moving from right to left. • Bring the compass close to the paper clip and move it all the way around the paper clip. Note the effect on the compass needle. Making list of observations recorded.

5. Domain Theory of MagnetismIn domain theory, the material is affected by the presence of a magnet if the atoms or molecules of the material are magnets. A domain is a group of adjacent atoms whose like poles have “like” orientations within the material. When the domains of a material are randomly oriented, the material shows no permanent magnetism. The presence of an external magnet can induce the domains to become aligned , more or less with that of the external magnet. Thus, the material becomes a magnet in its own right. In some magnetic materials, such as iron, the microscopic domains are easily reoriented in the direction parallel to the external applied field . How ever, when the external magnet is removed, the domains return to their random orientations and the magnetism disappears. The iron and such other materials form temporary magnets. In other materials, such as steel, the internal domains are reoriented only with considerable difficulty. When the external magnet is removed , however random re-alignment of the domains is also difficult. Thus the material will retain its magnetic properties. These types of materials form permanent magnets.

6. FerromagnetismSmall pieces of iron rubbed in one direction with lodestone become magnetized . Even bringing a piece of iron near a magnet causes the iron to be magnetized. Nickel and cobalt , and any alloy containing nickel, cobalt, or iron behave in the same way. These substances are called ferromagnetic, and you can induce them to become magnetized by placing them in a magnetic field.DemagnetizationDropping or heating an induced magnet will cause its aligned poles to return to random directions. Some materials, such as pure iron, revert to random alignment as soon as they are removed from the magnetizing field. Substances that can become instantly demagnetized are called soft ferromagnetic materials. Iron can be alloyed with certain materials, such as Aluminum and Silicon , that have keeping the dipoles aligned even when the magnetizing field is removed. These alloys are used to make permanent magnets and are referred to as hard ferromagnetic materials.Breaking a Bar Magnet Breaking a bar magnet produces two pieces of iron whose dipole alignment is identical to the original piece. Both pieces will also be magnets, with N-poles and S-poles at opposite ends. Continuous breaking will produce the same results, since the domains within the magnet remain aligned even when the magnet is broken.

7. Earth Magnet In 1600, William Gilbert, an English Scientist showed that the earth has the properties of a magnet. He fashioned a lodestone into the shape of a sphere (a model of Earth) . After using a compass to locate the poles of his lodestone sphere , he decided that, since it attracted the North pole of a compass, the magnet pole in the Arctic region of the Earth had to be a magnetic South-pole. The Antarctic region must contain a magnetic North-pole. A compass needle placed on the surface of Gilbert’s lodestone sphere behaved like a compass on the surface of Earth. He argued that Earth itself must be a giant spherical magnet. (Gilbert’s lodestone Sphere)Long before Gilbert’s time, it was noticed that a compass did not point directly towards true geographic north. In 1580, in London, it was recorded that a compass needle pointed 11 degree east of north. This is known as Magnetic Declination. To use a magnet compass effectively, you must be aware of the magnetic declination at your location on Earth. Detailed maps have been prepared that provide very accurate readings of the magnetic declination everywhere on Earth.

8. Law of Magnetic PolesOpposite Magnetic Poles attract.Similar Magnetic Poles repel. Magnetic Field of ForceThe space around a magnet in which magnetic forces are exerted.A magnetic field is represented by a series of lines around a magnet ,showing the path the N-pole of small test compass would take if it were to move freely in the direction of the magnetic force. Then, at any point in the field , a magnetic field line indicates the direction in which the N-pole of the test compass would point.

9. Lab. Activity: Magnetic Fields Instuctions:- • Cover the bar magnet with the sheet of acetate(or paper).Carefully sprinkle the iron filings onto the sheet of acetate around the bar magnet and look for any patterns formed by the iron fillings, especially near the poles of the magnet . Sketch any patterns that you find. • Use the compass to indicate the direction of the field around the space above the bar magnet. Draw a three-dimensional picture of the magnetic field around the magnet. • Repeat the procedure for the following cases:- (1) Like poles close to each other (2)opposite poles close to each other (3)magnets side by side To observe the magnetic force at a given point in a magnetic field we can use a small test compass with clearly marked poles. To demonstrate the magnetic field around a magnet, iron filings are sprinkled around the magnet. Materials: Two bar magnets, Iron filings, Sheet of Acetate (or paper), Small compass. Precautions: Be careful not to get iron fillings in your eyes. Wash your hands after handling iron filings.

10. Electromagnetism Hans Oerstead accidently discovered Electromagnetism. Prior to his discovery, Scientists believed that electricity and magnetism were separate phenomena. He proved that whenever electric current passes through a conductor , a magnetic field is produced around that conductor. The discovery of Electromagnetism has revolutionized the field of Magnetism. Now we are surrounded by magnetism. The supplies for electronic devices such as answering machines and calculators use magnetism to produce safe voltages. Electric motors, big cranes, cassette tapes, computer disks, credit cards, and pass cards involve magnetism.

11. Magnetism - a Gizmo- (a Computer-Based Simulation) In this activity students will observe the following activities on computer:- • Warm-up – Students discover which materials are ferromagnetic. • Activity A – Students determine when magnets attract one another and when they repel one another. • Activity B – Students observe magnetic field lines produced by lone magnets and pairs of magnets. • Extension – Students observe magnetic field lines produced by a magnet and other materials, some of which are ferromagnetic. All the students will work on this Gizmo at the following web site address:- http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=631 In this activity students will work in small groups. They will have to follow the code of conducts about the constructive use of computers. After this activity students will be able to Determine which materials are attracted to a bar magnet. Define the term "ferromagnetic." Observe the interaction of bar magnets. Determine that like poles repel and opposite poles attract. Understand that magnets exert force at a distance. Observe magnetic field lines for attracting and repelling magnets. Use magnetic field lines to predict if an object will be attracted to a magnet or repelled. Observe magnetic field lines produced by ferromagnetic materials At the end of the activity, students will be handed over a “Student Activity Sheet "to fill it out and return to the teacher. It will help to assess the students performance.

12. Applications of Magnetism in every day lifeThere are numerous applications of Electromagnetism in almost every field of life. Lifting electromagnets, electromagnetic relay, door chimes, electric bell, motors, transformers are few examples. Kitchen appliances, such as blender, food processor, vacuum cleaner, washing machine, dryer, Electric shaver. Most people are familiar with magnets primarily as toys, or as simple objects for keeping papers attached to a metal surface such as a refrigerator door.The invention of Magnetic Resonance Imaging(MRI) has revolutionized the field of Medical Science. It is a diagnostic technique that produces high quality images of the inside of the human body. It is a very clear improvement over X-rays and other methods of diagnosing illnesses. This life saving technology enables to see and study soft tissues of the body without the need for invasive exploratory surgery. Maglev Trains can move at speeds around 500 Km/hour . These high speed trains are already in operation in Japan, Germany and China. They rely upon magnetic fields to lift the train off the tracks( to reduce friction) and so are called Magnetic Levitation Trains. Magnetic fields are also used to propel the trains forward. They run on electricity and release no pollutants.

13. Curriculum Expectations Overall Expectations • F1. Analysethe social, economic, and environmental impact of electrical energy production and technologies related to electromagnetism, and propose ways to improve the sustainability of electrical energy production; • F2. Investigate, in qualitative and quantitative terms, magnetic fields and electric circuits, and solve related problems; • F3. demonstrate an understanding of the properties of magnetic fields, the principles of current and electron flow, and the operation of selected technologies that use these properties and principles to produce and transmit electrical energy. Specific Expectations • F3.1 Describe the properties of magnetic fields in permanent magnets and electromagnets (e.g., the three-dimensional nature of fields, continuous field lines, fields around current carrying conductors and coils) • F1.1Analysethe social and economic impact of technologies related to electromagnetism

14. Lesson Sequence for Magnetism • Introduction and History • Lab Activity, Making a magnet • Domain Theory, ferromagnetism and other important concepts of the topic. • Class demonstration about Magnetic Field lines with the help of iron fillings • Electromagnetism, its origin . Applications and uses in every day life. • A computer simulation “ Magnetism” in the form of a Gizmo • Review and Test

15. Teaching ideas and Assessment Strategies Teaching Ideas • Lecture Method including diagrams. • Journal Entries • Lab. demonstration • Group work on computer • Use of Internet • Problem Solving in Pairs • Jigsaw strategy to discuss applications of magnetism in important fields of life • Activity Sheets/ Revision Sheets. • Home work Assessment Strategies Students will be assessed from the activity sheets passed on by the teacher at the end of the class in addition to observation and journal entries Self- Assessment method will also be used In order to meet the achievement chart categories following tools will be used:- K/U Rubric, Inquiry Sheets, Communication Rubric, Applications marks sheets

16. Addressing common misconceptions of students • Some time students are confused about the poles of a magnet and geographical poles. It can be addressed from the idea of “ north seeking pole” and “south seeking pole” • In understanding the domain theory which is the basic of magnetization. They should try to memorize and understand the “Principals of Magnetism” • Students do not understand the three-dimensional nature of the magnetic field along a long, straight conductor. Careful observations during any activities and close attention to the construction of diagrams can help with this.

17. Back ground Knowledge • As this topic has not been studied in depth in previous grades, the students should refresh themselves with the following basics about the topic for their benefit • How did it all begin? • Who discovered magnets? • Who were the scientists who helped us to understand magnets? • What is magnetite? • What are magnetic force fields? • What is the rule of magnetism? • How does a compass work? • Who first used a compass? • Digging deeper into terrestrial magnetism. • What are some uses of magnets?

18. Safety First The slogan of work place “ Safety First” also applies in the Lab. work and class demonstrations. It is also covered under the curriculum expectations. • Be careful not to get iron fillings in your eyes. Wash your hands after handling iron filings. • Computer use should be constructive. Searching irrelevant sites is not allowed. • Be careful about the Paper clips and Bar magnets. Do not try to lift the other personal items with the help of magnets. • Lab. safety Policy is also in effect. Every one has to follow the sections of the policy in letter and spirit.

19. Accommodations Special need students and English Language Learners will be accommodated. Differentiated Learning will be in effect. Students who still have trouble in understanding the concepts can meet the teacher during break/recess or after school and they will have chance to take individual help from the teachers. Extra time will be given to ELL students to complete activity and test sheets. Group strategy will be used for problem solving. It will help special need students. Teacher will provide help to such students during the Gizmo lesson with reference to use of computer.

20. References • Grade 11 text books from Nelson, Addison Wesley, Pearson. • Ministry curriculum document grade 11 and 12 Science. • www.science.nelson.com • http://www.4dneuroimaging.com/html-pages/index.html • http://www.physics.ucla.edu/~msimon/ • http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=631