Magnetic Field

Content  
  • Method of Finding Magnetic Field Pattern
    1. Using Iron Filings
    2. Using Plotting Compass
  • Magnetic Field Pattern
    1. A Magnet
    2. Two Magnets
    3. Flat Magnets
    •   
    A magnetic field is the region around a magnet where a magnetic material experiences a magnetic force.

    Magnetic field is a vector quantity! It can be graphically represented by magnetic field lines which indicate its strength and direction.

    Using Iron Filings

    Procedure:
    Step 1: Place a hard thin piece of plastic on the magnet;
    Step 2: Sprinkle iron filings around it;
    Step 3: Tap the plastic gently and the iron filings will arrange themselves in a pattern that is similar to the magnetic field pattern.
    Step 4: Use a plotting compass to find the direction of the magnetic field lines.
    magnetic field Using Iron Filings
    Courtesy of PMT 4th Grade Science

    Using Plotting Compass

    Procedure:
    Step 1: Trace out the magnet at the center of the paper;
    Step 2: Start by positioning the compass near one pole of the magnet.
    Step 3: Mark out two dots, A and B that are aligned with the direction of compass needle.
    Step 4: Move the compass so that the end of the needle is now directly over B and mark out third dot C.
    Step 5: Repeat the process until the compass comes back to another pole of magnet.
    Step 6: Join all the dots and this will give the pattern of magnetic field line.
    Step 7: Repeat the whole process by starting at different points of magnet, a magnetic field pattern will be obtained.

    Magnetic Field Pattern of a Magnet

    • Outside the magnet, the magnetic field lines always start from N pole to S pole while Within the magnet, the lines continue from S pole to N pole. (However, these lines cannot be traced.)
    • Magnetic field lines must not cross each other.
    • The closer the field lines, the stronger the magnetic field.
    Note:
    • Magnetic field pattern is not just 2-dimension. It occurs in 3-dimension. This means when we place a compass above or below the magnet, it will still point from N pole to S pole of the magnet.
    • Without a magnet (external force), the compass always points to N pole of Earth.
    • With a magnet, under the influence of magnetic effect from the magnet, the compass will align and point along the direction of the magnetic field lines from the magnet at that point where it placed.
    3D Magnetic field
    Courtesy of UniServePhysics

    Magnetic Field Pattern between Magnets

    Note that point X is a neutral point where the magnetic fields from both magnets cancel out each other. There is no magnetic effect at X.

    Magnetic Field Pattern between Flat Magnets

    Note
    • Arc only occurs at the edge of flat magnets.
    • The magnetic field between two flat magnets are uniform, thus parallel magnetic field lines.
    Excel@Physics