1. Magnetism
Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons.
Like poles will repel, opposite poles will attract.
Magnetic field lines describe the structure of magnetic fields in three dimensions.
At the poles of a magnet, the magnetic field lines are closer together.
The strength of the magnetic field is greater where the lines are closer together and weaker where they are farther apart.

2. Magnetic Domains Moving electrons produce magnetic fields.
In most materials, these magnetic fields cancel one another and neutralize the overall magnetic effect.
In other materials, such as iron, cobalt, and nickel, the atoms behave as tiny magnets because of certain orientations of the electrons inside the atom.
These atoms are grouped in a tiny region called the magnetic domain.

3. The Earth is a Magnet
It exerts a magnetic forces and is surrounded by a magnetic field that is strongest near the North and South magnetic poles.
The Earth’s magnetosphere extends far out into space and is constantly bombarded by magnetic particles from the sun – “solar wind”.
How to remove magnetism
Drop the magnet
Heat the magnet
The Curie point is the temperature at which the magnetic properties of a substance are removed and is different for each substance.

4. Magnetic Fields Produced by Conductors
And how to switch on and off the strangely attractiveness

5. 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.

6. 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.

7. 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.

8. 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.

9. 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

10. 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.

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

12. 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.

13. 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.

14. 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.
The Right-Hand Rule

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

16. 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.

17. 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).

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

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