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Welcome to our Physics lesson on Magnetic Field Lines, this is the third lesson of our suite of physics lessons covering the topic of Introduction to Magnetism, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
The effect of magnetic field is understood better is we draw some imaginary lines (similar to those of electric field) to represent it. However, first we must do an experiment to determine the direction of magnetic field lines. This experiment is mentioned in the introduction part of this tutorial. When we place some iron filings on a paper and move slightly a bar magnet below the paper, the iron filings will align in the way shown in the figure:
This experiment is a demonstration that:
We represent the magnetic field lines through arrows starting from the North Pole and ending to the South Pole of magnet as shown below.
Magnetic field lines are not always curved. In U-shaped magnets for example, magnetic field lines in the shortest path from N-pole to S-Pole are straight, as shown in the figure.
Like electric field lines, magnetic field lines have a very important property: they do not cross each other. This means the magnetic field changes gradually through a predictable process.
Remark! A magnet is a piece of metal that is coloured in the factory in which it is produced. The red and blue colour are just conventional signs; magnets are coloured to help the user identify which is the N-pole and which is the S-pole of magnet.
The following table summarizes the properties of magnetic field and comperes them to the properties of electric field discussed in Section 14.
From the above table we can deduce other properties of magnets such as:
The magnet in the figure is cut in four equal pieces.
What is the polarity of the new magnets obtained?
Since the edges of the original magnet are not affected by the cutting process, they keep the original polarity and every new polarization is made by taking into account the fact that all magnets have two opposite poles. Therefore, the four small magnets will have the polarities as shown in the figure below.
You have reached the end of Physics lesson 16.1.3 Magnetic Field Lines. There are 9 lessons in this physics tutorial covering Introduction to Magnetism, you can access all the lessons from this tutorial below.
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