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Magnetic Forces, Fields, and Oersted

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MAGNETIC FORCES, FIELDS, AND OERSTED S PRINCIPLE Lesson 10 A magnet is a material or object that produces a magnetic field. The distribution of a magnetic force in ... – PowerPoint PPT presentation

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Title: Magnetic Forces, Fields, and Oersted


1
Magnetic Forces, Fields, and Oersteds Principle
  • Lesson 10

2
  • A magnet is a material or object that produces a
    magnetic field.
  • The distribution of a magnetic force in the
    region of a magnet.
  • Magnets are labelled North and South and have the
    same field laws as electric charges.
  • Similar magnetic poles repel and dissimilar poles
    attract.

3
  • To map a magnetic field a test compass can be
    used. Much like a test charge, a test compass
    will point north in line with the south field.

4
  • Magnetic forces can act between some metals that
    are not magnetic. These metals are called
    Ferromagnetic metals and include metals such as
    cobalt, iron, nickel, or mixtures of the three.

5
  • The atomic structure of these metals seems to
    make them strongly magnetic. Think of magnetic
    materials, being made up of a lot of smaller
    magnets.

6
Domain Theory of Magnets
  • All large magnets are made up of many smaller and
    rotatable magnets, called dipoles, which can
    interact with other dipoles close by. If dipoles
    line up, then a small magnetic domain is
    produced.

7
Electromagnets
  • Force at a distance is the common element between
    electrostatics and magnetism. Hans Oersted
    studied this and came up with the following
    principle.
  • Charge moving through a conductor produces a
    circular magnetic field around the conductor.

8
  • Mapping the magnetic field of a conductor enables
    one to be able to predict the direction of the
    electromagnetic force from the current.
  • There are several hand signs developed to predict
    how magnetic forces will act.

9
Left-hand rule 1 for Conductors (LHR 1)
  • Grasp the conductor with your left hand such that
    the thumb points in the direction of the electron
    (-) current flow. The curved fingers point in the
    direction of the circular magnetic field around
    the conductor.

10
  • Using this rule allows us to produce a weak
    magnet that we can turn on and off.
  • To make the electromagnet stronger and straighten
    out the field so that it is more like a bar
    magnet, the wire conductor is made into a coil.
    The individual field lines fall on top of each
    other strengthening the entire field. Coiling the
    wires also straightens out the field.

11
Left hand rule 2 (LHR2)
  • Grasp the coiled conductor with the left hand
    such that the curled fingers point in the
    direction of the electron (-) current flow
    through the conductor. The thumb points in the
    direction of the magnetic field within the coil.
    Outside the coil, the thumb represents the north
    (N) end of the electromagnet produced by the
    coil.

12
  • This allows us to create a magnet that acts like
    a bar magnet but that can be tuned off when it
    needs to be. The other advantage is that strength
    of the electromagnet can be controlled by the
    following factors.

13
1. Current in the coil
  • The greater the current flow, the greater the
    field strength. Strength varies directly as the
    current in the coil.

14
2. Number of turns in the coil
  • The greater the number of coils, the greater the
    field strength. Strength varies directly as the
    number of turns in the coil of the current is
    constant.

15
3. Type of material in the coils centre
  • The more ferromagnetic the material within the
    coil, the greater the magnets strength. Iron is
    one of the better materials to use.

16
4. Size of the coil
  • the smaller the diameter of the coil, the
    stronger the magnetic field.

17
Questions
  • Given the direction of current flow in the
    conductor seen below, find the direction of the
    magnetic field.  
  • Given the direction of the magnetic field, find
    the direction of the current in the conductor
    seen to the right.
  • What happens to the strength of the magnetic
    field around a coil if the current through the
    conductor is increased from 1.0 A to 2.5 A?
    (Hint Look at the 4 factors that affect
    electromagnetic strength.)

Current
18
  • What would happen to the field strength if the
    number of turns in the coil of the electromagnet
    were reduced by half and the current remained the
    same? (Hint Look at the 4 factors that affect
    electromagnetic strength.)
  •  
  • What would happen to the strength of an
    electromagnet if over time the conductor started
    to corrode and increased the resistance of the
    conductor?
  •  
  • What would happen to the strength of the
    electromagnet if the coiled conductor started to
    unwind causing the diameter of the coil to
    increase?
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