Magnetism Unit Notes 1

1. Magnetism UnitNotes 1 Grade 10 ST

2. Magnetic Behaviour • After watching the demo, what conclusions can you make about what you saw? ______________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. What is Magnetism? • Magnetism is the force of attraction or repulsion in and around a material • Magnetism is present in all materials but at such low levels that it is not easily detected • Certain materials such as magnetite, iron, steel, nickel, cobalt exhibit magnetism at levels that are easily detectable

4. What is a Magnet? • A magnet is any piece of material that has the property of attracting iron (or steel). • Magnetite, also known as lodestone, is a naturally occurring rock that is a magnet. • This natural magnet was first discovered in a region known as Magnesia in Greece and was named after the area in which it was discovered.

5. What is a Magnet? Cont’d • Magnetism may be naturally present in a material or the material may be artificially magnetized by various methods. • Magnets may be permanent or temporary. • After being magnetized, a permanent magnet will retain the properties of magnetism indefinitely. • A temporary magnet is a magnet made of soft iron, that is usually easy to magnetize; however, temporary magnets lose most of their magnetic properties when the magnetizing cause is discontinued.

6. Different Types of Magnetic Materials Magnetic • A permanent magnet • Two magnetized objects can attract or repel each other

7. Different Types of MagneticMaterials Ferromagnetic • Materials which can be magnetized are called ferromagnetic materials • They contain iron, nickel or cobalt • They are attracted to magnetic objects, they become temporarily magnetized • Example: Iron • Iron is made up of a set of regions called domains. • Each domain acts like a tiny magnet with it’s own north and south poles • When iron is not magnetized= domains are not aligned • When iron is magnetized domains are aligned

8. Different Types of MagneticMaterials Non- magnetic • Non-magnetic objects do not react to the presence of a magnet. They are not attracted or repelled!

9. Temporary vs. Permanent Magnets

10. Magnetic Properties • http://www.ndt-ed.org/EducationResources/HighSchool/Magnetism/magneticproperties.htm • After watching the above applet, explain what happens when a magnet is broken into smaller pieces ____________________________________________________________________________________________________________________________________________________

11. Magnetic Properties • Magnets can be cut into smaller and smaller pieces indefinitely • All magnets have a north seeking and south seeking pole • Each new piece makes a new magnet with it’s own north and south poles. • The NORTH POLE of a magnet is the end that naturally seeks the earth’s magnetic pole near the geographic north pole

12. Magnetic Properties • Magnets interact with each other through forces of attraction and repulsion • In general, the following is true of magnetic poles • Opposite magnetic poles attract • Like magnetic poles repel each other Question: Knowing this, is the North Pole a North Pole or a South Pole? _____________________________

13. Magnetic Properties Check • If the north pole of a magnet is moved toward the south pole of another magnet, will the north pole be subjected to an attractive or a repulsive force? Explain your answer. ____________________________________________________________________________________________________________________________________________________

14. Interesting Article • http://www.scientificamerican.com/article.cfm?id=cattle-deer-sense-magnetic-field&print=true

15. Magnetic Fields • In a magnetized object, the domains are all lined up in the same direction. • Any magnetized object produces a magnetic field. The magnetic field is the area around the magnet where the magnetic force can be felt.

16. Magnetic Fields • To draw the magnetic field, we use arrows. • Most magnets have 2 poles: north (N) and south (S) • Two possible forces exist between magnetized objects • Attraction • Repulsion

17. Magnetic Field around a bar magnet Arrows are always pointing towards the south

18. Compasses How do compasses work? • The north needle of a compass always points in the same direction as the magnetic field.

19. Magnetic field around a straight wire • When there is a current flowing through a wire, there is a magnetic field around the wire. • The shape of the magnetic field is individual circles around the wire.

20. Magnetic Field around a Straight Wire To determine the direction of the magnetic field lines we use the “Right Hand Rule” • Place your right thumb along the direction of the current. • Your fingers curl in the same direction as the magnetic field

21. Magnetic Field around a Straight Wire Try it… _ +

22. Magnetic Field around a Straight Wire • In a circuit • With Compass

23. Magnetic Field around Electromagnets • When there is a current flowing through a coiled wire, there is a magnetic field that is created we call it an electromagnet. • The shape of the magnetic field around the electromagnet is exactly the same as around a bar magnet

24. Magnetic Fields around Electromagnets • To determine the location of N and S, we use the “Second Right Hand Rule” • Place your fingers on your right hand so that they curl in the same direction as the current. • Your thumb indicates north

25. Magnetic Fields around Electromagnets • Try it… • With Compass

26. Factors that affect the strength of an electromagnet • To increase the strength of an electromagnet: • Increase current • More coils • Type and gauge of the conductor • The core material

27. Induction in an Electromagnet • To generate a magnetic field:

28. Induction in an Electromagnet • To generate an electric current: