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Four magnetic materials are nickel, iron, cobalt and steel.
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Poles are ends of a magnet where the magnetic field is strongest.
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Unlike poles attract each other.
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Like poles repel each other.
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Repulsion is the only sure way to find out if an object is a magnet or not.
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Magnetic Induction: When an unmagnetized material is attracted to a magnet, the material itself becomes a magnet. This phenomenon is called magnetic induction.
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Magnetic materials have tiny regions called domains which act as “mini-magnets”. When these domains are lined up, the material becomes a magnet. If the domains point in random directions then the material does not behave as a magnet.
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Methods of making magnets are:
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stroking a steel bar repeatedly with a permanent magnet
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putting the steel bar in a solenoid (coil) having direct current (D.C.)
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Methods of demagnetization of magnets are:
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heat until red-hot
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hammer repeatedly (or subject to some other impact)
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Alternating current (A.C.) in a solenoid (coil) with the magnet inside of it
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Remove magnet slowly from inside of the coil OR
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Gradually decrease the current to zero
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Two variations of Right-hand Grip Rule:
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Magnetic field: It is the region of space where a magnetic object experiences a magnetic force.
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Experiment to plot field lines of a magnetic field.
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Mark at one end of compass needle.
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Move compass so that the other end of compass needle is on the mark AND re-mark.
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Repeat along one line and join the dots.
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Repeat with different start points to draw more lines.
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Direction of field lines is from N-pole to S-pole.
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Iron is easier to magnetize and demagnetize than steel. This means that iron makes a stronger magnet when placed inside a current carrying solenoid. It also loses magnetism when the current is switched off.
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An electromagnet consists of insulated copper wire wound on a core of soft iron.
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The strength of magnetic field of a solenoid can be increased by:
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increasing number of turns
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increasing current
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using iron core
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Iron is used to shield sensitive equipment from magnetic fields. It carries those fields along the metal.
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Reed switch consists of two pieces of soft iron called reeds. When these reeds are magnetized they are attracted to each other. Current flows when they make contact.
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