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Electromagnets. Oersted noticed that a compass needle moves whenever it is placed near a conducting wire. Oersted`s Principle : A charge moving through a conductor produces a circular magnetic field around the conductor.

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Presentation Transcript
slide2

Oersted noticed that a compass needle moves whenever it is placed near a conducting wire.

Oersted`s Principle: A charge moving through a conductor produces a circular magnetic field around the conductor.

  • To determine the direction of the circular magnetic field (clockwise or counter clockwise) we use the Left Hand Rule (LHR) for straight conductors
slide3

Using your left hand,

Your thumb shows the direction of electron flow and your fingers wrap around the conductor in the direction of the magnetic field lines.

slide4

Don’t confuse LHR with RHR (in the book) that shows flowof positive charges.

  • We use the designation of an X to show the flow of electrons going into the paper (face on), and the designation of a to show the flow of electrons coming out of the paper.
  • Dashed lines in concentric circles represent the magnetic field lines which are closest together (strongest) nearest the conducting wire.
solenoids
Solenoids

We can straighten out these magnetic field lines by “bending” the conductor into circles. This actually strengthens the magnetic field since the field lines become superimposed on one another. The advantage of this strategy is being able to create a strong magnet that can be turned on or off with current flow (electromagnet). This has many applications like stereo speakers, school bells, car remote devices.

slide6

To determine the direction of the magnetic field when current is travelling through a coiled conductor we use the Left Hand Rule (LHR) for coiled conductors.

Using your left hand,

Your thumb shows the direction of north magnetic fieldand your fingers wrap around the conductor in the direction of the electron flow.

strength of coiled magnets
Strength of Coiled Magnets

The magnetic field strength can be varied by:

  • Current (more current increases magnetic field)
  • Number of coils (more coils increases magnetic field)
  • Size of coil (smaller diameter increases field strength)
  • Type and amount of ferromagnetic conductor can increase magnetic field strength
slide9

Magnetic field strength is measured in units of Tesla (T)

  • 1 Tesla equals 1 Newton of magnetic force when 1 Ampere of current travels through 1 metre of conductor
  • Or 1 T = 1 N

mA