# Magnetic Fields Produced by Conductors

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Magnetic Fields Produced by Conductors
13.3 and 13.4: The Right Hand Rule and Magnetic Fields of Solenoids And how to switch on and off the strangely attractiveness

Effects of Domain Theory
Magnetic Induction Demagnetization Reverse Magnetization Breaking a Bar Magnet Magnetic Saturation Induced Magnetism by Earth Keepers for Bar Magnets Magnetic Induction The process of magnetizing an object from a distance by aligning the domains in the same direction Demagnetization When iron becomes demagnetized, its aligned dipoles return to random directions. Reverse Magnetization Bar magnets reversing direction. Breaking a Bar Magnet Breaking a bar magnet produces two pieces of iron whose dipole alignment is identical to the original piece. Magnetic Saturation Occurs when the maximum amount of dipoles in a material are aligned. Induced Magnetism by Earth If a piece of iron is held in Earth’s magnetic field and its atoms are agitated, either by heating or by mechanical vibration, its dipoles will align. Keepers for Bar Magnets Keepers are stored with bar magnets across the ends to stop demagnetization.

Oersted’s Discovery In 1819, the Danish physicist Hans Christian Oersted ( ) discovered the connection between electricity and magnetism by accident while lecturing at the University of Copenhagen. He noticed that a compass needle placed closely to a current carrying wire would take up a position nearly perpendicular to the direction of the current.

Principle of Electromagnetism
Whenever an electric current moves through a conductor, a magnetic field is created in the region around the conductor. Oersted discovered the Principle of Electromagnetism. Whenever an electric current moves through a conductor, a magnetic field is created in the region around the conductor.

Magnetic Field of a Straight Conductor
The magnetic field lines for a straight conductor are concentric circles around the conductor. The magnetic field lines for a straight conductor are concentric circles around the conductor. As the distance from the conductor increases, the field gets weaker and the lines become more widely spaced. There are no poles; the field lines are continuous and give the direction of the plotting compass at every point. Reversing the direction of electric current through the conductor causes the field lines to point in the opposite direction, though their pattern remains the same. A circle (wire) with an X represents current flowing into the page and a circle with a dot represents current flowing out of the page.

If a straight conductor is held in the right hand with the right thumb pointing in the direction of the electric current, the curled fingers will point in the direction of the magnetic field lines. The Right-Hand Rule

Parallel Wires Currents travelling through two parallel wires in the same direction will attract. Currents travelling through two parallel wires in the opposite direction will repel.

How is the scrap metal held up by the crane?
If magnet -> how is it released? Electromagnet

Electromagnets A device that exerts a magnetic force using electricity. The magnetic field around a straight conductor can be intensified by bending the wire into a loop. The magnetic field around a straight conductor can be intensified by bending the wire into a loop. The loop can be thought of as a series of segments, each an arc of a circle, and each with its own magnetic field. The field inside the loop is the sum of the fields of all the segments. The field lines become more like lopsided ovals.

Coil or Solenoid The magnetic field can be further intensified by combining the effects of a large number of loops would close together to form a coil, or solenoid. The field lines are straight, almost equally spaced, and all point in the same direction. We call this a uniform magnetic field. The magnetic field is of the same strength and is acting in the same direction at all points. If the direction of electric current is reversed, so are the field lines.

The Right-Hand Rule If a coil is grasped in the right hand with the curled fingers representing the direction of electric current, the thumb points in the direction of the magnetic field inside the coil.

Parallel Coils Coils with currents travelling in the same direction will attract. Coils with currents travelling in the opposite direction will repel.

Factors Affecting the Magnetic Field of a Coil
Current in the Coil The more current, the greater the concentration of magnetic field lines in the core. Number of Loops The more loops, the stronger the magnetic field since the magnetic field is the sum of the field of each loop. Type of Core Material The core of a coil can greatly affect the coil’s magnetic field strength. A core of iron will increase the strength compared to that of air.

Type of Core Material The core material becomes an induced magnet, as its atomic dipoles align with the magnetic field of the coil. The core itself becomes an induced magnet. The factor by which a core material increases the magnetic field strength is called the material’s relative magnetic permeability (K).

Ferromagnetism Materials that become strong induced magnets when placed in a coil. Iron, nickel, cobalt, and their alloys. Paramagnetism Materials that magnetize slightly when placed in a coil and increase the field strength by a barely measurable amount. Oxygen and aluminum. Diamagnetism Materials that cause a very slight decrease in the magnetic field of a coil. Copper, silver, and water. Core materials are divided into three groups according to their relative magnetic permeability.

Applications of Electromagnetism
Lifting Electromagnet Electric Bell Electromagnetic Relay – switch is closed by the action of an electromagnet.