Permanent magnets, Grade 10 Physics

Physics 10.VII Magnetism T.Trường 10/6/17 962 0
  1. Permanent magnets, Grade 10 Physics
    1/ The poles of permanent magnets

    Because the domains in a permanent magnet all line up in a particular direction, the magnet has a pair of opposite poles, called north (usually shortened to N) and south (usually shortened to S). Even if the magnet is cut into tiny pieces, each piece will still have both a N and a S pole. These poles always occur in pairs. In nature we never find a north magnetic pole or south magnetic pole on its own.
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    Magnetic fields are different to gravitational and electric fields. In nature, positive and negative electric charges can be found on their own, but you never find just a north magnetic pole or south magnetic pole on its own. On the very small scale, zooming in to the size of atoms, magnetic fields are caused by moving charges (i.e. the negatively charged electrons).

    2/ Magnetic attraction and repulsion
    Like poles of magnets repel one another whilst unlike poles attract. This means that two N poles or two S poles will push away from each other while a N pole and a S pole will be drawn towards each other.
    Definition: Attraction and Repulsion
    Like poles of magnets repel each other whilst unlike poles attract each other.
    Worked Example : Attraction and Repulsion
    Question:
    Do you think the following magnets will repel or be attracted to each other?
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    Answer
    Step 1 : Determine what is required

    We are required to determine whether the two magnets will repel each other or be attracted to each other.
    Step 2 : Determine what is given
    We are given two magnets with the N pole of one approaching the N pole of the other.
    Step 3 : Determine the conclusion
    Since both poles are the same, the magnets will repel each other.

    Worked Example : Attraction and repulsion
    Question:
    Do you think the following magnets will repel or be attracted to each other?
    [​IMG]
    Answer
    Step 1 : Determine what is required

    We are required to determine whether the two magnets will repel each other or be attracted to each other.
    Step 2 : Determine what is given
    We are given two magnets with the N pole of one approaching the S pole of the other.
    Step 3 : Determine the conclusion
    Since both poles are the different, the magnets will be attracted to each other.

    3/ Representing magnetic fields
    Magnetic fields can be represented using magnetic field lines. Although the magnetic field of a permanent magnet is everywhere surrounding the magnet (in all 3 dimensions), we draw only some of the field lines to represent the field (usually only 2 dimensions are shown in drawings).
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    In areas where the magnetic field is strong, the field lines are closer together. Where the field is weaker, the field lines are drawn further apart. The strength of a magnetic field is referred to as the magnetic flux
    Important:
    1. Field lines never cross.
    2. Arrows drawn on the field lines indicate the direction of the field.
    3. A magnetic field points from the north to the south pole of a magnet.
    Activity :: Investigation : Field around a Bar Magnet
    Take a bar magnet and place it on a flat surface. Place a sheet of white paper over the bar magnet and sprinkle some iron filings onto the paper. Give the paper a shake to evenly distribute the iron filings. In your workbook, draw the bar magnet and the pattern formed by the iron filings. Draw the pattern formed when you rotate the bar magnet as shown.
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    As the activity shows, one can map the magnetic field of a magnet by placing it underneath a piece of paper and sprinkling iron filings on top. The iron filings line themselves up parallel to the magnetic field.
    Another tool one can use to find the direction of a magnetic field is a compass. The compass arrow points in the direction of the field.
    [​IMG]
    Activity :: Investigation : Field around a Pair of Bar Magnets
    Take two bar magnets and place them a short distance apart such that they are repelling each other. Place a sheet of white paper over the bar magnets and sprinkle some iron filings onto the paper. Give the paper a shake to evenly distribute the iron filings. In your workbook, draw both the bar magnets and the pattern formed by the iron filings. Repeat the procedure for two bar magnets attracting each other and draw what the pattern looks like for this situation. Make a note of the shape of the lines formed by the iron filings, as well as their size and their direction for both arrangements of the bar magnet. What does the pattern look like when you place both bar magnets side by side?
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    As already said, opposite poles of a magnet attract each other and bringing them together causes their magnetic field lines to converge (come together). Like poles of a magnet repel each other and bringing them together causes their magnetic field lines to diverge (bend out from each other).
    [​IMG]

    High School Students Studying the Sciences Physics
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