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Magnetism Chapter 7

Magnetism Chapter 7. J. C. Rowe Course Instructor. Basic Facts: Magnet originates from the G reek word “ magnetite ” A magnetite is a naturally magnetic ore. Natural elements that are strongly attracted to magnets are called ferromagnetic ex. Iron, nickel, cobalt.

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Magnetism Chapter 7

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  1. MagnetismChapter 7 J. C. Rowe Course Instructor

  2. Basic Facts: • Magnet originates from the Greek word “magnetite” • A magnetite is a naturally magnetic ore. • Natural elements that are strongly attracted to magnets are called ferromagnetic ex. Iron, nickel, cobalt

  3. Magnetic properties are shown by the charges of an element, so all the electrons in atoms are charges in motion. Therefore all moving electrons should act like tiny magnets. But this isn't true because the magnetic fields produced by individual electrons are very weak but when tiny magnetic fields overlap in proper orientation in areas called magnetic domains, they become a bigger and stronger magnetic field. In natural magnets enough magnetic fields work together to produce a noticeable magnetic properties that we can actually see

  4. Magnetic Poles • A magnet has 2 poles • South pole or negative pole • North pole or positive pole • Like poles repel while opposite poles attract • If you break a bar magnet you will end up 2 magnets

  5. All magnets make a magnetic field. You can not see this field but you can map it by placing a piece of paper over a magnet and pour iron fillings on top. You would something like the picture below.

  6. Earth and Magnetism • The south pole of earths magnetic field is actually located near the earths geographic north pole. • The earths magnetic poles change on a daily basis • So • From a magnetic stand point when we head in the direction of the geographic north, are we headed to the magnetic North or Magnetic South ?

  7. Magnetic field around current carrying wires Danish physist Hans Christian Oersted discovered the connection between electricity and magnetism. He completed a circuit which caused a deflection of a near by compass

  8. Determining the Direction of the Current by Right Hand Rule: Point the thumb of your hand in the conventional currents direction (into or out of the page) opposite to flow if it is given. Curl fingers in. that is the direction of the magnetic field around the wire

  9. Deduce the Magnetic Field Direction • If you are told electron flow is to the Right of this slide… where is the current direction ? • If you are told the electron flow is towards the ceiling… where is the current flow? Where is the direction of the magnetic flow ? Use the Right Hand Rule… • What if the electron flow is pointing to the ground ?

  10. Magnetic Fields Around a Solenoid • A solenoid is a coil around a piece of metal. • Ex. A wire around a nail. • Creates a stronger magnetic field • Solenoid acts as a bar magnet (develops south/north pole)

  11. Right Hand Rule for Solenoids: Find conventional from the front of 1 of the loops Point your finger in the direction of the conventional current Your fingers will be pointing south Curl fingers to show direction of magnetic field

  12. Magnetic Field Strength • All magnets are a different shape, size, and strength • The magnitude of the force experienced by a charged object moving perpendicularly through a magnetic field • F=qvB • F is force • Q is particle charge • V is velocity • B is strength of magnetic field • When it is not perpendicular • F = qsinX • B=F/qvsinX

  13. HOW TO FIND THE MAGNITUDE OF THE FORCE OF A WIRE IN THE MAGNETIC FIELD: F= I L B SINX F = Force I = Current L = Length B = Magnetic Field X = angle (when force is parallel magnetic force is equal to zero)

  14. Right Hand Rule for Straight Wires: Point thumb in the direction of velocity for positive opposite direction for negative Point index finger to the direction of magnetic field Point middle finger of your right hand in the direction that is perpendicular to both thumb and the index. This gives the direction of force

  15. Electromagnetic Induction: Experiments showed that moving or turning a wire will induce a current. found by Michael Faraday and Joseph Henry. This was one of the biggest discoveries in history.

  16. Magnetic flux: Is the change in current by increasing the number of loops or turning the wire. Magnetic flux= magnetic field x area where field passes x Cos of angle Theta  angle = angle between the field lines & the surface of the area they pass through

  17. Faraday’s Law The instantaneous EMF resulting from magnetic induction equals the rate of change of magnetic flux Or…. Any change in the magnetic environment of a coil of wire will cause a voltage (EMF) to be "induced" in the coil. .. This induced EMF is = rate of change of flux

  18. Faradays law: Lenz’s Law: An induced EMF (voltge) gives rise to a current whose magnetic field apposes the change in magnetic flux that produced it.

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