ferromagnetic material

temporary and permanent magnets

Materials that have been magnetized may become temporary or permanent magnets. If you bring a bar magnet close to pile of paper clips, the paper clips will become temporarily magnetized, as all their magnetic domains line up. As a result, the paper clips will stick to the magnet and also to each other (see the Figure 1.2). However, if you remove the paper clips from the bar magnets magnetic field, their magnetic domains will no longer align. As a result, the paper clips will no longer be magnetized or stick together. If you stroke an iron nail with a bar magnet, the nail will become a permanent (or at least long-lasting) magnet. You can see how its done in the Figure 1.3. The nails magnetic domains will remain aligned even after you remove the nail from the magnetic field of the bar magnet. Q: Even permanent magnets can be demagnetized if they are dropped or heated to high temperatures. Can you explain why?

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what makes a material magnetic

Magnetism is the ability of a material to be attracted by a magnet and to act as a magnet. Magnetism is due to the movement of electrons within atoms of matter. When electrons spin around the nucleus of an atom, it causes the atom to become a tiny magnet, with north and south poles and a magnetic field. In most materials, the north and south poles of atoms point in all different directions, so overall the material is not magnetic. Examples of nonmagnetic materials include wood, glass, plastic, paper, copper, and aluminum. These materials are not attracted to magnets and cannot become magnets. In other materials, there are regions where the north and south poles of atoms are all lined up in the same direction. These regions are called magnetic domains. Generally, the magnetic domains point in different directions, so the material is still not magnetic. However, the material can be magnetized (made into a magnet) by placing it in a magnetic field. When this happens, all the magnetic domains line up, and the material becomes a magnet. You can see this in the Figure 1.1. Materials that can be magnitized are called ferromagnetic materials. They include iron, cobalt, and nickel.

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magnetite

Some materials are natural permanent magnets. The most magnetic material in nature is the mineral magnetite, also called lodestone (see Figure 1.4). The magnetic domains of magnetite naturally align with Earths axis. The picture on the left shows a chunk of magnetite attracting small bits of iron. The magnetite spoon compass shown on the right dates back about 2000 years and comes from China. The handle of the spoon always points north. Clearly, the magnetic properties of magnetite have been recognized for thousands of years.

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instructional diagrams

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questions

all materials respond to magnetic force.

a. true

-->  b. false

nonmagnetic materials include

a) wood.

b) glass.

c) plastic.

-->  d) all of the above

magnetism is due to the movement of electrons within atoms.

-->  a. true

b. false

all of the following materials can be magnetized except

a) iron.

-->  b) carbon.

c) cobalt.

d) nickel.

if you stroke an iron nail with a bar magnet, the nail will become a temporary magnet.

a. true

-->  b. false

a permanent magnet can be demagnetized by

a) dropping it.

b) heating it.

c) cooling it.

-->  d) two of the above

diagram questions

No diagram questions associated with this lesson