What have we learned from the labs? Magnets and Magnetism What have we learned from the labs?

Activity: What kinds of objects are attracted to a magnet? Iron, nickel, cobalt and alloys containing these elements are attracted to a magnet.

Diamagnetic have a weak, negative susceptibility to magnetic fields. slightly repelled by a magnetic field does not retain the magnetic properties when the external field is removed most elements in the periodic table, including copper, silver, and gold

Paramagnetic have a small, positive susceptibility to magnetic fields slightly attracted by a magnetic field does not retain the magnetic properties when the external field is removed magnesium, molybdenum, lithium, and tantalum

ferromagnetic have a large, positive susceptibility to an external magnetic field exhibit a strong attraction to magnetic fields able to retain their magnetic properties after the external field has been removed strong magnetic properties due to the presence of magnetic domains iron, nickel, and cobalt

Activity: How can the strength of magnets be compared Different methods can be used to compare the strength of different magnets. They can used to pick up paper clips and the number of paper clips picked up by the magnet can be compared.

Activity: Where is a magnet strongest? A magnet is strongest at the poles. A magnet has two poles – north pole and south pole.

More on Magnet’s poles When a magnet is broken into smaller pieces, each small piece will have its own north and south poles.

Activity: Which way is north? The north direction is when the directional compass points The north pole of a bar magnet points in the north direction. A compass needle is a small bar magnet.

Activity: How do magnets affect one another? Unlike poles attract, like poles repel.

Earth’s poles If like poles repel and unlike poles attract, why is the north pole of a bar magnet pointing towards the north direction? Does this violate the law of magnetic poles?

Earth’s poles Earth has two poles, magnetic and geographic.

Earth’s poles

So what is the cause of all magnetism? Moving charges Electrons circling the nucleus of an atom cause magnetism In most substances, equal numbers of electrons spin in opposite directions, which cancels out their magnetism.  In substances such as iron, cobalt, and nickel, most of the electrons spin in the same direction. This makes the atoms in these substances strongly magnetic.

Magnetic domains The strength of the magnet depends on the arrangement of the magnetic domains of the magnet Magnetic domains are regions of 1012 to 1015 atoms when magnetic moments of these atoms are aligned parallel the material is said to be “magnetized”

Magnetic domains