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AWIM Basic Electricity Class Experiment No. 5 On Magnetism (Physics CH 19) January 2017

Learn about magnets, magnetic poles, magnetic field direction, and the Earth's magnetic field in this informative session. Discover how a solar storm creates the stunning celestial light show known as the Aurora Borealis.

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AWIM Basic Electricity Class Experiment No. 5 On Magnetism (Physics CH 19) January 2017

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  1. AWIM Basic Electricity ClassExperiment No. 5On Magnetism(Physics CH 19)January 2017

  2. How a solar storm creates a celestial light show: Aurora Borealis? October 2012 WSJ

  3. What should we learn in this session? Magnets, Magnetic Poles, and Magnetic Field Direction (Ch 19.1) Experiment with a magnet and Iron dust Geomagnetism: The Earth’s Magnetic Field (Ch 19.8) Does the Earth behave like a big magnet? Magnetic Field Strength and Magnetic Force (Ch 19.2) Electromagnetism: Define Magnetic Field strength and Magnetic Force exerted on a moving electric charge. Rigth-Hand Force Rule Quiz No. 5a Magnetic Forces and Current Carrying Wire (Ch 19.4) How to create a magnetic field? Oersted’s experiment in 1820 What is the significance of Ampère experiment? What are some important magnet applications? New Terminology Quiz No. 5b Homework No. 5

  4. Magnets, Magnetic Poles, and Magnetic Field Direction (Ch 19.1) Is lodestone a magnet? A piece of lodestone like that shown above was used by ancient mariners because of its magnetic features. Ancient people knew that lodestones, when suspended from a string and allowed to rotate freely, would come to rest horizontally, pointing North-South. A lodestone attracts iron nails and has polarity. It exhibits two poles, North and South. The lodestone can be found on Earth’s surface. It consists of magnetite (a ferromagnetic material).

  5. What is a magnet? A magnet (from Greek magnetis) is a material or object that produces a magnetic field with two poles, North and South. Its magnetic field is invisible but is responsible for the most notable property of a magnet: A force that pullson other ferromagnetic materials, such as iron, and attracts or repels other magnets. N N N S Repels Attracts

  6. Ferromagnetic Materials Iron, Ferrite, a classic ferromagnetic material; Nickel mixed with Iron (Earth’s inner core); Cobalt; Permalloy is 20 % Iron and 80% Nickel (1000 times stronger magnetic field that of Steel); Samarium-Cobalt is very brittle and has a three times higher magnetic field permeability than Ferrite. It is characterized by a small externally imposed magnetic field that causes its magnetic “domain” to line up and be magnetized. Alnico refers to a family of iron alloys which in addition to iron are composed primarily of aluminum (Al), nickel (Ni) and cobalt (Co) hence al-ni-co. They also include copper and sometimes titanium. Alnico alloys are ferromagnetic, with high resistance to loss of magnetism and are used to make permanent magnets. Rare earth magnets are developed in search of even higher magnetic strength (usually scandium and yttrium are hard to separate). Ferromagnetic materials can be divided into magnetically "soft" materials like annealed iron (steel for example), which can be magnetized but do not stay magnetized, and “hard” materials, which do, like permanent magnets.

  7. Magnetic field lines of force of a bar magnet With a typical bar magnet for example, the magnetic field B (magnetic field strength), extends from the north pole to the south pole outside the magnet, and back from south to north inside the magnet. Unlike the electric field the magnetic field always forms a closed loop. The iron filings behave like tiny compasses and line up with the magnetic field. The field is not made up of positive or negative charges but pairs of poles. It is measured in terms of its force F and its direction. The direction of the magnetic field, B at any location is the direction that the north pole of the compass would point if placed at that location. 7

  8. Experiment with a Magnet and Iron Dust With magnetic field’s presence, the iron fillings become magnetized and line up within the direction of the field. Just as electric fields exist in the neighborhood of electric charges (E = F/q), magnetic fields surround permanent magnets. However since magnetic monopoles don’t exist, the magnitude of the magnetic field, B is defined in terms of the magnetic force exerted on a moving electric charge as (B = F/qv), discussed in section 19.2. In the following magnet field experiment a compass could follow the strongest of magnetic field around and demonstrate an invisible magnetic field’s presence.

  9. Experiment with a Magnet and Iron Dust Instructions: • Use a bar magnet or a speaker magnet, a sheet of paper and a very small amount of fine iron dust. • Lay the sheet of paper on top of the magnet and sprinkle some iron dust on top. • Move the paper and observe the iron dust in motion. • Use of a compass can (visually)demonstrate the invisible presence of a magnetic field. • When finished place the iron dust in the paper cup.

  10. Geomagnetism: The Earth’s Magnetic Field (C19.8) Does the Earth behave like a big magnet? The Earth’s Magnetic field is similar to that of a bar magnet’s. It has the MagneticNorth and South Poles with an axis separate from the Earth’s Geographic axis. What are the general characteristics of the Earth’s Magnetic field?

  11. Earth’s mantle plasma in its liquid form has very high temperatures. At a depth of 100 Km iron Curie temperature is 770oC. The Curie temperature (TC), is the temperature at which certain materials lose their permanent magnetic properties, to be replaced by induced magnetism. The Curie temperature is named after Pierre Curie who showed that magnetism was lost at a critical temperature.

  12. General characteristics of the Earth’s magnetic field; and theories about its possible source The Earth’s magnetic field has similar characteristics to that of a bar magnet. How is it formed? There are several theories. A simple bar magnet theory is ruled out because of very high temperatures at which iron loses its permanent magnetic properties. The Earth’s magnetic field is believed to be associated with motions in the liquid inner core deep within the planet. At the center of the Earth lies the core which is twice as dense as the mantle because its composition is metallic (iron-nickel) rather than stony. It is made up of two parts: a liquid 2,200 km-thick outer layer and a 1,250 km-thick solid inner core. As the earth rotates, the liquid outer core spins thus inducing the Earth’s magnetic field.

  13. Two South East Pacific deep ocean ridges with different magnetic polarity as detected by submarines.

  14. North Magnetic Pole Positions Since 1600 Location of the North Magnetic Pole and the North Geomagnetic Pole in 2016. Victoria Island, Canada, West of Greenland

  15. Ways in which the Earth’s magnetic field affects our planet’s local environment The Geomagnetic poles are the intersections of the Earth's surface and the axis of a bar magnet hypothetically placed at the center the Earth by which we approximate the geomagnetic field. The Magnetic poles are the points at which magnetic needles become vertical. There also are "the magnetic north pole" and "the magnetic south pole". Geographic Pole

  16. Magnetic Declination The angular difference between magnetic north and “true” Geographic North Pole is called magnetic declination which varies with time. The map shows isogonic lines (same magnetic declination) for the USA.

  17. Aurora Borealis: the northern lights Solar particles trapped in the Earth’s magnetic field ionize air atoms; on recombination of the atoms, the light is emitted. “As the Sun nears the height of its 11-year cycle, the eerie northern lights caused by charged solar particles spewing across space are becoming more intense, stretching as far south as Michigan. Sunspot activity, geomagnetic storms and solar flares are expected to peak next year (2013), when the current solar cycle reaches its peak.”October 2012 WSJ

  18. Magnetism in Nature • Humans navigating by use of compass • Birds migration • Magnetotactic bacteria migration in oceans N

  19. Magnetic Forces and Current Carrying Wire (Ch 19.2, 19.4) How to create a magnetic field? Oersted’s experiment in 1820 What is the significance of Ampère experiment? Oersted noted to his surprise that every time the electric current was switched on, the compass needle moved.

  20. Magnetic Field Strength and Magnetic Force (Ch 19.2) Define magnetic field strength and determine the magnetic force exerted by a magnetic field on a moving charge particle. • Experiments indicate there is a connection between electrical properties of objects and how they respond to magnetic fields. Electromagnetism is a study of interactions between electrically charged particles and magnetic fields. • Consider the horseshoe magnet in the presence of a moving electric charge q+.There must exist a centripetal force that is perpendicular to the particle’s velocity to cause its particle’s velocity deflection. An electric force is not present. The gravitational force is too weak. Therefore, the force must be due to the interaction of the moving charge and the magnetic field, B. B = F/qv [T (Tesla) = N/Am] F = qvB (v perpendicular to B) F = qvB sin θ Note: 1 T, N/Am is too large for most applications. 1 G (Gauss) = .0001T; Earth’s magnetic field = .0 to3G; Superconducting material = 25T

  21. Magnetic Forces and Current Carrying Wire (Ch 19.4) Calculate the magnetic force on the current carrying wire. F = Σq x vB; v = L/t [m/s] F = Σq/t x LB; Σq/t = I [A] F = I x LB; [ N= AxmxN/Am] F = ILB sin θ; Electric current is composed of many electric charges. Each electric charge moving in a magnetic field is acted on by a force unless it is moving parallel to or directly opposite the direction of the field. θ θ

  22. Exercise, Ch. 19.4: Magnetic Forces on Current Carrying Wire A 2 m long current carrying wire of 20A in a magnetic field of 50mT whose direction is at an angle of 370 from the direction of the current. Find the force on the wire. X perpendicular to B B 370 I 530 Ix Ix θ Vertical current component to the magnetic field axis, Ix is applied to determine the projected current vector value. Ix = I x sin530 = 20 A x .62; L= 2m; B = 50mT =20x10-3T; F = IxLBsinθ F = 20 x.62 x 2 x 50x10-3 [AmTx(N/AmT)]; Reminder: B=F/qv [T=N/Am] F = 1.24 N

  23. What did Ampère demonstrate? If a current in a wire created a magnetic force on a compass needle, two such wires also should interact magnetically. while the opposing currents in two loops repel each other.

  24. Magnetism is a physical phenomenon produced by the motion of electric charge • Magnetism is a physical phenomenon produced by the motion of electric charge, resulting in attractive and repulsive forces between objects. Magnetic field is a region around magnetic material or around a moving electric charge within which acts the force of magnetism. • All magnetism is due to circulating electric currents. In magnetic materials the magnetism is produced by electrons orbiting within the atoms; in some materials such as iron, a net magnetic field can be induced by aligning the atoms. • Solar flairs for example, that emit a stream of electric charges reach our planet. They are deflected by the the Earth’s magnetic field. It is a good example of interactive relationship between between magnetic field and electrons in motion. (See the introductory slide.)

  25. Oersted's and Ampère’s Compass Experiment Needed: a compass; a one-foot (30 - 35cm) length of wire, insulated and scraped bare at the ends; a 1.5 volt electric size “D” battery. Use sand paper to strip the wire varnish one inch at each end. Lay the compass on a table, face upwards. Wait until it points north.   Lay the middle of the wire above the compass needle, also in the north-south direction. Bend the ends of the wire so that they are close to each other. Use the putty to stabilize the two ends of the wire close to the compass.

  26. Oersted's Compass Experiment Cont’d Test No. 1: Grab one end of the wire in one hand and press against one end of the battery. Grab the other end with your other hand, and press momentarily against the other terminal of the battery. The needle will swing strongly by up to 90 degrees. Quickly disconnect! The needle will swing back to the north-south direction. Note that no iron is involved in producing the magnetic effect! Test No. 2: Repeat with the connections of the battery cell reversed. Note that the needle now swings up 90 degrees in the opposite direction. Test No. 3: Move the wire 4-5 inches above the compass. Repeat with the connections of the battery cell reversed as in Test No. 2. Note that the needle now swings up 90 degrees in the opposite direction but less than in Test No. Record all test measurements on the Data Sheet

  27. Test No. 4 Repeat Test No. 1. The compass is pointing North. Note the measurement. Add another cell with an opposite polarity. Align this wire with the compass. Note the final angular direction: ________ degrees. Has the compass returned to its original position? ____________ Explain why___________________________________________ Copy your results on the Data Sheet: Test No. 4

  28. Test No. 5 What is needed to conduct the Test no. 5? 1. Team of two students; 2. Two batteries and two wires; 3. One compass; Test instructions: Repeat Test No. 1 with exception that each student uses a separate battery cell and apply a separate wire loop with the same current polarity across the compass. The compass moves either East or West. Note the angular position: ________ degrees. Is the measured angular position larger than in Test No. 1? Compare the results in Test No. 1 with Test No. 5 and explain the difference: _____________________________________________________________________ Copy your results on the Data Sheet: Test No. 5

  29. Test No. 6 Repeat Test No. 5 with exception that student 1 apply in the electric wire loop the opposite current polarity from student 2. Note the compass final angular position:________ degrees. Is the compass pointing North? Explain why? __________________________________________________________________ Copy your results on the Data Sheet: Test No. 6

  30. Compass Test Data Sheet Name:_____________________ Test No. 1: Note the compass final angular direction: 0 to + _____ degrees Test No. 2: Note the compass final angular direction: 360 to _____ = _____ degrees Why has the compass moved in the opposite direction: __________________________ _______________________________________________________________________ Test No. 3: Note the compass final angular direction: 360 to _____? =_____degrees Why has compass moved less in Test No. 2: ___________________________________ _______________________________________________________________________ Test No. 4: Note the compass final angular direction: ________ degrees. Has the compass returned to its original position? ____________ Explain why___________________________________________ Test No. 5: Note the compass final angular direction: ________ degrees. Compare the results in Test No. 1 with Test No. 5 and explain the difference: _____________________________________________________________________ Test No. 6: Note the compass final angular direction: ________ degrees. Is the compass pointing North? Explain why? ___________________________________________

  31. Devices that use Permanent Magnets • Permanent magnets are used in many situations where a fixed and constant magnetic field is required. • Magnets are used in permanent magnet motors. These motors control the power windows and windshield wipers of your car. • They’re found in acoustic transducers, magneto mechanical devices, imaging systems, televisions, telephones, computers, audio systems. • Alnico magnets are used in radar and telephones. Ceramic magnets are even used on lawnmowers. • Rare earth magnets can ruin computer monitors, media and even credit cards. 35

  32. SI Electromagnetism Units Symbol Name Unit SI Conversion I Electric current Ampere A = C/s q Electric charge Coulomb C = As F Capacitance Farad F = As/V or q/V E Electromotive force, Potential difference Volt J/C = (kgm2/s3)/A) ρ Resistivity Resistivity Ωm P Electric power Watt W = kgm2/s3 E Electric field strength Volt per meter V/m H Magnetic field strength Ampère per meter A/m μ Permeability henry per meter H/m = Tm/A = kgm/(As) B Magnetic flux density, Induction (F/qv) Tesla T = Wb/m2 = N/Am T Magnetic Field Tesla T Vs/m2 = N/Am = Wb/ms2 μ0 Permeability of free space 4 π x 10-7 N/A-2 F Force of motion N 1 N = 1 kg m/s2 v Velocity m/s Ω Resistance Ohm V/A = 1 Ω = 1 kg·m2·s-3·A-2 in Length Inch 0.0254 m or 25.4 mm Wb Magnetic Flux Weber 1 V·s = 1 T·m2 = 1 J/A; J Joule (work, electric energy, heat) 1Nm; 1kgm2/s2 = Nm = Ws = CV = 2.39 x 10-4 kcal = 9.48 x10-4 BTU P Power hp or W or Vxq/t 550 ft-lb/s = 1 W Kg Kilogram mass 1N N= 1.0 kg x 9.8m/s2

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