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Magnetism: Intro

Magnetism: Intro . Physics 12. Clip of the day:. Minutephysics….. How far is a second? http://www.youtube.com/watch?v=Wp20Sc8qPeo&list=PLED25F943F8D6081C. Review Question:.

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Magnetism: Intro

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  1. Magnetism: Intro Physics 12

  2. Clip of the day: • Minutephysics….. • How far is a second? • http://www.youtube.com/watch?v=Wp20Sc8qPeo&list=PLED25F943F8D6081C

  3. Review Question: • A soccer ball is kicked horizontally off a 22.0-meter high hill and lands a distance of 35.0 meters from the edge of the hill. Determine the initial horizontal velocity of the soccer ball. • ANSWER: 16.5 m/s

  4. Magnet Brainstorm….and play time! • Are all magnets alike? • What kind of things do magnets attract? • Which part of the magnets are strongest? • How can you tell where the poles are? • How can you tell which is which? • Do magnets work through other materials? • What does it depend on? • Can you make a magnet out of a nail?

  5. Shall we start with Bill Nye on magnets? • http://www.youtube.com/watch?v=ak8Bh9Zka50

  6. Magnetism: • Magnets have 2 poles (north and south) • Like poles repel • Unlike poles attract • Magnets create a MAGNETIC FIELD around them

  7. Magnetic Force: • Magnetic forces have properties that are similar to electric and gravitational force in that: • The force varies following an inverse square relationship due to the separation of poles • The force varies directly with the strength of the poles • However, since we don’t have magnetic monopoles there is no equation for magnetic force

  8. Magnetic Domains: • Within a magnetic compound, there are many different magnetic domains • If these are randomly arranged, the material is not magnetic • If they are aligned, the material will be magnetic

  9. Temporary vs Permanent Magnets: • Some materials will easily align the domains in the presence of a magnetic field; however they will usually return to a random arrangement after the field is removed; these are called temporary magnets (like iron) • Other materials will not easily align the domains, however once aligned they will remain aligned; these are called permanent magnets (like steel)

  10. Magnetic Field Lines: • It is possible to map a magnetic field in a manner similar to that of electric or gravitational fields • Convention says field lines go from north to south

  11. Magnetic Field: • Symbol =B • SI units =tesla (T) T = N__ A• m

  12. Electric Charges and Magnetic Poles: • In 1819, Oersted noticed that a current carrying wire would create a magnetic field • This was the first step into the realm of electromagnetism • Oersted’s experiment led to Right Hand Rule #1

  13. Oersted’s experiment • When there is no current the needle of the compass points north • When the circuit is complete, electricity flows and the compass needles deflected • There must be some forces causing the deflection…magnetic force!

  14. Why does the needle move? THE WIRE ITSELF MUST BE MAGNETIC!!! In other words the wire has its own INTERNAL MAGNETIC FIELD that is attracted or repulsed by the EXTERNAL FIELD. As it turns out, the wire’s OWN internal magnetic field makes concentric circles round the wire.

  15. Electromagnetism: • Moving electrons produced a magnetics field • A changing magnetic field causes electrons to move

  16. Right Hand Rule 1: • The direction of magnetic field lines around a current carrying wire can be determined using a right hand rule • Thumb = direction of current • Fingers curl around in direction of magnetic field

  17. Ampere’s experiment: • Ampere discovered that when compasses were placed close to a current carrying wire the compass would be deflected based on the direction of the current

  18. A the needles are moving counter clock wise • B the needles are moving clock wise

  19. Ampere theorized that the magnetic fields between two charge carrying wires would either result in attractive or repulsive forces • Based on this, Ampere was able to develop an equation to describe the magnetic field

  20. Magnetic Field: Force (N) Magnetic field (T) Length of wire (m) Current (A) Number of turns For a solenoid: Length of each turn (m)

  21. Sample problem:

  22. Try it: • Page 767 • 1 a, b, c and 2 • Page 778 • 1-4

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