1. Magnetism Unit Notes 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 Magnetic Materials 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 Magnetic Materials 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 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.cf m?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: