magnets

magnetic force and magnetic field

The force that a magnet exerts on certain materials, including other magnets, is called magnetic force. The force is exerted over a distance and includes forces of attraction and repulsion. North and south poles of two magnets attract each other, while two north poles or two south poles repel each other. A magnet can exert force over a distance because the magnet is surrounded by a magnetic field. In the Figure 1.2, you can see the magnetic field surrounding a bar magnet. Tiny bits of iron, called iron filings, were placed under a sheet of glass. When the magnet was placed on the glass, it attracted the iron filings. The pattern of the iron filings shows the lines of force that make up the magnetic field of the magnet. The concentration of iron filings near the poles indicates that these areas exert the strongest force. You can also see how the magnetic field affects the compasses placed above the magnet. When two magnets are brought close together, their magnetic fields interact. You can see how they interact in the Figure 1.3. The lines of force of north and south poles attract each other whereas those of two north poles repel each other.

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magnetic poles

A magnet is an object that attracts certain materials such as iron. Youre probably familiar with common bar magnets, like the one shown in the Figure 1.1. Like all magnets, this bar magnet has north and south magnetic poles. The red end of the magnet is the north pole and the blue end is the south pole. The poles are regions where the magnet is strongest. The poles are called north and south because they always line up with Earths north-south axis if the magnet is allowed to move freely. (Earths axis is the imaginary line around which the planet rotates.) Q: What do you suppose would happen if you cut the bar magnet pictured in the Figure 1.1 along the line between the north and south poles? A: Both halves of the magnet would also have north and south poles. If you cut each of the halves in half, all those pieces would have north and south poles as well. Pieces of a magnet always have both north and south poles no matter how many times you cut the magnet.

instructional diagrams

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questions

only bar magnets have north and south magnetic poles.

a. true

-->  b. false

if you cut a bar magnet in half, one half will have just a north pole and the other half will have just a south pole.

a. true

-->  b. false

a magnets force is

a) a force of repulsion only.

b) a force of attraction only.

-->  c) exerted over a distance.

d) two of the above

when two magnets are brought close together, their magnetic fields interact.

-->  a. true

b. false

lines of force around two magnetic poles push apart when

a) both poles are north poles.

b) both poles are south poles.

c) one pole is a north pole and one pole is a south pole.

-->  d) two of the above

diagram questions

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