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Magnetism
This document discusses magnetism and magnetic fields. It begins by defining a magnet and different types of magnets. It then explains magnetic materials, domains, and magnetic field lines. The document discusses how cutting a magnet in half would affect its poles. It also covers permanent and temporary magnets, as well as how magnetism can be induced using electricity or electromagnets. The final section provides a sample lab experiment to test magnetic fields and determine which magnet has the strongest field.
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Magnetism
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- 2. In your labnotebook, please answer as best you can: 1. What do I, V, and R stand for in Ohm’s Law? • I = current, V = voltage, and R = resistance 2. What does current measure? • 1 ampere = 1 Coulomb per second of electrons flowing past a point 3. Explain electrical resistance. • Resistance = opposition to electron flow. The more tightly a material’s atoms hold onto electrons, the greater the electrical resistance. Resistance is measured in units of ohms (Ω). 4. How are static electricity and current electricity different? • Static is a momentary discharge of accumulated electrons while current electricity is a continuous flow of electrons. 4. What do DC and AC stand for in electricity? • DC = Direct Current, AC = Alternating Current Bonus Question: Is it possible to have lightning in outer space? Why or why not? No: electrical discharge of lightning requires matter (atoms to donate electrons and matter to move through). Review Quiz 9
- 3. Experiment 9 Magnetic Fields • Observation –What do you know about magnets and magnetic fields? • – What do you want to figure out? (Ask a question) • Which magnet has the strongest field? • Where is the field strongest in each magnet? • Hypothesis – What do you think will happen? (Answer your questions) • • Experiment – How can we test our hypothesis? • Which side picks up staples? • How close to staples can magnet go? – What data should be recorded? • Conclusion – Was your hypothesis correct? – How was/should the experiment be modified?
- 4. Magnets • A magnetis any material that produces a magnetic force (push or pull) on a magnetic material (such as iron) – closely related to electricity, but different • Where there is electricity, there's a magnetic field • Where there's magnetic field, electricity can be created
- 5. Magnetic Materials • Notall metals are magnetic – 3 Are naturally magnetic (ferromagnetic) • Iron • Nickel • Cobalt • Aluminum is NOT magnetic • Some Lanthanides form strong magnets – Rare Earth magnets – Neodymium & Samarium – Gadolinium is magnetic only at low temperatures • Must be cooled to be magnetic • Used in MRIs (Magnetic Resonance Imaging)
- 6. Magnetite • Lodestone is magnetizedmagnetite – means "leading stone" – used in early compasses – possibly made by lightning • Naturally occurring magnetic igneous rock – Contains iron oxide (Fe3O4) • Found on black sand beaches and deserts • Largest US deposit in NY (Adirondack mountains)
- 7. Types of Magnets AlnicoMagnetsFlexible Magnets Ceramic Magnets Neodymium Rare Earth Magnets: (very strong) Samarium Cobalt (SmCo)
- 8. Magnetic Poles • Everymagnet has two poles – North & South • same poles repel • opposites attract
- 9. Magnet Interactions • Likepoles repel – North repels North – South repels South • Opposite poles attract
- 10. Magnetic Fields • Linesshow areas of force exerted in a region around a magnet – closer lines show greater force – force is strongest near the magnet • Force originates from N pole and moves towards S pole
- 11. Magnetic Domains • Thespin of electrons create tiny magnetic regions called domains –In some atoms, these domains cancel out –In magnets, domains are all lined up in same direction • Whenever all electrons spin in the same direction, a magnetic field is produced
- 12. • Domains stayaligned within the magnet – dipoles present in each new piece • What would happen to the poles if we cut this magnet in half? • Does size determine magnetic strength? - In general, yes. • But it’s not the only factor.
- 13. Experiment 9 Magnetic Fields • Observation •A magnet is any material that produces a magnetic force • Iron, nickel & cobalt are naturally magnetic (ferromagnetic) • Some rare earth metals form strong magnets • Flexible magnets are plastic with tiny iron bits mixed in • Opposite poles attract, like poles repel • Magnetic fields extend all around a magnet – Different fields interact/combine – More/closer field lines = stronger force – QUESTION: • Which magnet has the strongest field? • Where is the field strongest in each magnet? • Hypothesis • I think the largest magnets will be the strongest because they have the most “pulling” material. • The magnetic field will be strongest at the North Pole. • Experiment – Procedures: • Describe each magnet • Draw field using iron filings & compass • Record # of staples lifted off table. – Touch pile for 2 seconds, then lift slowly – Test N, S, and middle of each magnet • Conclusion – Summarize results – Was your hypothesis correct? – How was/should the experiment be modified? Magnet Type Magnetic Field # of Staples Ceramic bar N:15 S: 16 Mid: 7 Neodymium disc N: 43 S: 45 Mid: 15 Oval hematite N: 27 S: 18 End: 11
- 14. Permanent Magnets • Fieldcan be lost or removed – Heating to the Curie Point – Sending an Electric Current through • Degaussing • Magnetic storage media erased – Banging It • dislodges aligned domains Substance Curie temp °C Iron (Fe) 770 Cobalt (Co) 1130 Nickel (Ni) 358 Iron Oxide (Fe2 O3 ) 622 • Electron spins (domains) are aligned • Retains its own magnetic field • Examples: Refrigerator Magnets, Bar Magnets, Lodestone, Horseshoe Magnets, Hematite, etc…
- 15. Temporary Magnets • Domainstemporarily line up • Will keep magnetic field only until tampered with –Examples: • Paperclips, scissors, staples, thumb tacks, pins, screwdrivers, refrigerator door, car door locks, etc… • Anything that is magnetic, but will not keep its field
- 16. Making a TemporaryMagnet • Magnetic Induction – domains are aligned by touching or bringing it near a magnet – only in some materials • Strength of magnet determines: – strength of induced field – how long induced magnetism lasts • Object loses its magnetism once magnet is removed – Temporary magnets can also be made using electric currents
- 17. Magnetism From Electricity •Electricity is the movement of electrons in a single direction through a conductor – Aligned flow of electrons creates a magnetic field • Similar to electron domains lining up in a permanent magnet • Every wire carrying electricity has a weak magnetic field around it • Ever wonder why dust bunnies collect around power cords?
- 18. Electromagnets • An electromagnetis created by running electric current around a magnetic material – usually a copper solenoid with an iron core • magnetic field disappears when electric flow is removed • poles are reversed if terminals are swapped • More current = stronger field
- 19. Adjustable Magnets Strength controlledby: –Neatness of coiling –Number of loops –Wire gauge –Battery strength –Magnetic permeability of the core material –Temperature
Editor's Notes
- #3 1 Coulomb = 6.25 x 1018 electrons
- #6 Raw data: 10130 101270 99130 95120 8860 8770 84180 8335 8315 82150 8090 8090 72120 6760 6560 6520
- #7 Write on Dry Erase board what you want them to write in lab book. Experiment Procedure: Write a brief description of a magnet in a table in your lab notebook. (1 inch ceramic bar, 5mm neodymium disc, etc.) Using iron filings and/or a compass, draw the magnetic field surrounding the magnet. Record the # of staples the magnet can pick up. Which pole will be used in each magnet & how will that be determined? How close can the magnet come to the pile of staples? Any other variables to control?
- #9 Gadolinium is ferromagnetic at temperatures below 20 C (68F) - Must be frozen to be magnetic
- #10 Fe(II)Fe(III)2O4
- #11 Flexible magnets are manufactured by mixing Ferrite or Neodymium magnet powders and synthetic or natural rubber binders. Flexible is manufactured by rolling (alendaring)or extrusion methods. Versatility, low cost, and ease of use are among the reasons to choose ferrite based flexible magnets for your application. This magnet material is usually manufactured in strip or sheet form and it is used in micro-motors, gaskets, novelties, signs, and displays. Ferrite flexible magnet material is very low energy and it does not usually replace fully dense magnet materials. Ceramic magnets are made of ferrite (iron). Ceramic magnet material (Ferrite) is Strontium Ferrite. This material is one of the most cost effective magnetic materials manufactured in industry. The low cost is due to the cheap, abundant, and non-strategic raw materials used in manufacturing this alloy. The permanent magnets made with this material lend themselves to large production runs. This magnet material has a fair to good resistance to corrosion and it can operate in moderate heat. The majority of the world¡¯s Ceramic magnetic material comes from China because of the alloy¡¯s commodity nature and the high tooling costs found in the west. Ceramic magnets have a low Energy Product and they are usually used in an assembly containing mild steel. Alnico magnet alloy is largely comprised of Aluminum, Nickel, Cobalt and Iron. Alnico is a moderately expensive magnet material because of the Cobalt and Nickel content. This alloy has very good corrosion resistance and a high maximum operating temperature. Some grades of this alloy can operate upwards of 550•C. Magnets made with this alloy are available in a variety of grades and dimensions and they are usually cast and finish ground to size. Alnico magnet material is a mature technology and it has a relatively low Energy Product (BHmax) . This material is now mainly used in military, aerospace, older proprietary designs and in applications where the magnet will be exposed to elevated temperatures Rare Earth Magnets are called such because Neodymium and Samarium (of which they are made are found in the rare earth elements on the periodic table. Both Neodymium and Samarium Cobalt alloys are powdered metals which are compacted in the presence of a magnetic field and are then sintered. Neodymium, or Neo, is made up of Neodymium Iron and Boron and is moderate in price. With poor corrosion resistance this alloy is usually plated or coated (Examples: Nickel Plated, Epoxy Coated, Parylene Coated). Neodymium is offered in a range of operating temperatures depending on your application (80•C to 200•C). Premium Neodymium Alloys capable of operating above 120•C can become quite expensive. This permanent magnet material has many intellectual property rights associated with it and there are a limited number of licensed manufacturers in the world. Many infringing manufacturers from the Pacific-rim dump sub par material into the Western markets. This magnet material is extremely powerful and it has allowed for the miniaturization of many products from HDD (Hard Disc Drives) and motors to novelties and audio devices. Neodymium permanent magnets usually offer the best value when comparing price and performance. Samarium Cobalt (SmCo) Magnets are alloys of the Lanthanide group of elements. SmCo magnets are available in a number of different grades that span a wide range of properties and application requirements. Rare Earth magnets are the most advanced commercialized permanent magnet materials today. SmCo magnets are brittle and machining operations should be performed prior to magnetization, using diamond tools. SmCo magnets are anisotropic, and can only be magnetized in the orientation direction.
- #12 Write on Dry Erase board what you want them to write in lab book. Experiment Procedure: Write a brief description of a magnet in a table in your lab notebook. (1 inch ceramic bar, 5mm neodymium disc, etc.) Using iron filings and/or a compass, draw the magnetic field surrounding the magnet. Record the # of staples the magnet can pick up. Which pole will be used in each magnet & how will that be determined? How close can the magnet come to the pile of staples? Any other variables to control?
- #13 Similar to electric charges: negative and positive - you can never have a monopole magnet (with just one pole)
- #15 If you bring two like-poles of magnets together, you can feel the force opposing them. Similarly, you feel (and see) the attraction between two opposite poles.
- #16 Write on Dry Erase board what you want them to write in lab book. Experiment Procedure: Write a brief description of a magnet in a table in your lab notebook. (1 inch ceramic bar, 5mm neodymium disc, etc.) Using iron filings and/or a compass, draw the magnetic field surrounding the magnet. Record the # of staples the magnet can pick up. Which pole will be used in each magnet & how will that be determined? How close can the magnet come to the pile of staples? Any other variables to control?
- #19 Write on Dry Erase board what you want them to write in lab book. Experiment Procedure: Write a brief description of a magnet in a table in your lab notebook. (1 inch ceramic bar, 5mm neodymium disc, etc.) Using iron filings and/or a compass, draw the magnetic field surrounding the magnet. Record the # of staples or paper clips the magnet can pick up. OR record distance first attraction is noted Which pole will be used in each magnet & how will that be determined? How close can the magnet come to the pile of staples? Any other variables to control? (time/distance held, person holding/recording)
- #20 Write on Dry Erase board what you want them to write in lab book. Experiment Procedure: Write a brief description of a magnet in a table in your lab notebook. (1 inch ceramic bar, 5mm neodymium disc, etc.) Using iron filings and/or a compass, draw the magnetic field surrounding the magnet. Record the # of staples the magnet can pick up. Which pole will be used in each magnet & how will that be determined? How close can the magnet come to the pile of staples? Any other variables to control?
- #21 A cow magnet is a preventive veterinary medical device for cattle. Traditionally, cow magnets were strong alnico magnets about 1cm by 8cm (0.4 by 3.1 inches) in the shape of a smoothed rod, but today they are more commonly several ring-shaped ferrite magnets attached to a stainless-steel or plastic core, in the same shape as the single-piece original. A rancher or dairy farmer feeds a magnet to each calf at branding time; the magnet settles in the rumen or reticulum and remains there for the life of the animal. When the cow grazes, it often consumes and swallows what is called tramp iron: baling and barbed wire, staples, nails, and other metallic objects. These objects are indigestible and would lodge in the reticulum and cause inflammation resulting in lower milk production (for dairy cattle) or lower weight gain (for feeder stock). This condition is called hardware disease. The cow magnet attracts such objects and prevents them from becoming lodged in the animal's tissue. While the resultant mass of iron remains in the cow's rumen as a pseudobezoar (an intentionally introduced bezoar), it does not cause the severe problems of hardware disease. Cow magnets cannot be passed through a cow's 4th bonivial meta-colon.
- #23 The term was first used by (then) Cmdr Charles F. Goodeve, RCNVR, during World War II while trying to counter the German magnetic mines that were playing havoc with the British fleet. The mines detected the increase in magnetic field when the steel in a ship concentrated the Earth's magnetic field over it. Admiralty scientists, including Goodeve, developed a number of systems to induce a small "N-pole up" field into the ship to offset this effect, meaning that the net field was the same as background. Since the Germans used the Gauss as the unit of the strength of the magnetic field in their mines' triggers (this was not yet a standard measure), Goodeve referred to the various processes to counter the mines as degaussing. The term became a common word. Until recently, the most common use of degaussing was in CRT-based TV sets and computer monitors. For example, many monitors use a metal plate near the front of the tube to focus the electron beams from the back. This plate, the shadow mask, can pick up strong external fields and from that point produce discoloration on the display.
- #25 Demo/Lab: U