CH 19: Magnetism

• Magnetic field is a region where magnetic forces are felt, and if we pour some iron fillings around bar magnets, magnetic field line patterns will be formed.
• Magnetic field is felt as repulsion or attraction, and a magnet always has two poles: a north pole (N) and a south pole (S).
• Magnetization in a magnetic material is when electrons orbiting the nuclei or the atoms have magnetic properties, and each atom acts like a miniature magnet.
• A group of atoms form a magnetic domain where the magnetic fields of these atoms are aligned and point in the same direction.
• Magnetization is a process of aligning the magnetic domains in a magnetic material.
• Magnetization can be achieved by stroking a magnetic material with a permanent magnet, or using a solenoid with alternating current.
• Demagnetization is a process of removing the magnetic properties of a magnet, and can be achieved by heating, physical impact, or withdrawing it slowly from a solenoid with alternating current.
• A soft iron block can be induced with a soft pole and another end can be induced as a north pole.
• The earth has a weak magnetic field surrounding it, which gives a compass needle a magnetic force and hence the needle always points towards the earth's geographical north pole.
• Induced magnetism is the process where a magnetized material becomes a magnet when near a magnet, this is known as induced magnetism.
• If a bar magnet is broken into smaller pieces, it will become a smaller magnet.
• A large thin sheet of iron placed below a bar magnet will divert the magnetic field through it, making the area below the sheet a shielded area protected from the influence of the external magnetic fields.
• Permanent magnets have various applications including magnetic door catches in freezers and refrigerators, electric motors, electric generators, and long speakers.
• An iron ring placed between the north pole of one magnetic bar and the south pole of another magnetic part will divert the magnetic field through it, making the area inside the iron ring a shielded area protected from the influence of the external magnetic fields.
• Magnetic field lines represent the magnetic field around a magnet, with the needle of a compass always pointing towards the same direction as the magnetic field lines.
• Temporarily magnet can be used to separate magnetic objects from non-magnetic objects, and can also be used in transformers or to lift heavy objects which it can be found in cranes.
• Magnetic shielding is the process where self-magnetic materials are used to divert magnetic field lines through themselves and away from the components or devices.
• The number of magnetic field lines from the north pole is equal to the number of magnetic field lines terminating at the south pole.
• If a compass is placed at point x, it will not experience any magnetic force from any of the bar magnet, indicating that there is no magnetic field line at this point.
• A magnetic field is a region where a magnet or a magnetic material experiences a magnetic force.
• Induced magnetism can attract other magnetic materials, making it a permanent magnet.