# CHAPTER 6 Magnet and Magnetism_revised.doc.pdf - PHY150...

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PHY150 JMS/2019 1 CHAPTER 6: MAGNET & MAGNETISM 6.1 The Modern Theory of Magnetism Magnetism in matter is currently believed to result from the movement of electrons in the atoms of substances. The magnetic polarity of atoms is thought to arise primarily from the spin of electrons about their own axis and partially due to their orbital motions around the nucleus. The atoms in a magnetic material are grouped into microscopic magnetic regions called domains. In this domain, all the atoms are believed to be magnetically polarized along a crystal axis. In unmagnetized material, these domains are oriented in random direction. a) unmagnetized material b) magnetized material 6.2 Magnetic Field A magnetic field is a space around a magnetic material in which a charged particle will be exerted by a magnetic force.

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PHY150 JMS/2019 2 Magnetic field is represented by magnetic field lines. A magnetic field line has direction and its strength is indicated by the concentration of field lines. The higher the concentration of field lines, the stronger is the magnetic field. The magnetic flux density B is a measure of the strength of magnetic field at a point. It is a vector quantity also known as magnetic field strength. Its unit is weber per square meter (Wb m -2 ). 1 Wb m -2 = 1 tesla (T). 1 T = 10 -4 gauss (G) The direction of the magnetic field at a given location is the direction in which the north pole of a compass points when placed at that location. S N Magnetic field lines exit from the north pole of a magnet and enter at the south pole. The field lines continue even
PHY150 JMS/2019 3 within the body of a magnet. In fact, magnetic field lines always form closed loops. This means that there is no monopole. 6.3 Types of Magnetic Field Permanent magnet Magnets always have two poles. The magnetic field line exits from the north pole and enter at the south pole.

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