magnetism

Submitted by:Robina Delos Santos

Brenda PerosJan Denise Espinas

Charmaine Rose Ortiz

♥ The class of phenomena exhibited by a magnetic field.

♥ The study of magnets and their effects. ♥ The force exerted by a magnetic field. ♥ Unusual power to attract, fascinate, or influence. ♥ To describe how materials respond on the

microscopic level to an applied magnetic field; to categorize the magnetic phase of a material.

♥ The force where objects are attracted or repelled to one another. Usually these objects are metals such as iron.

Oersted & the Magic of Magnetism

♥ Hans Christian Oersted - a professor of Physics at the

Copenhagen University, who discovered that there is a magnetic field around current-carrying conductors (or wires).

Some Facts about Magnets♥ The Earth is a giant magnet. It has two poles, the “magnetic north

pole” & the “magnetic south pole”. ♣ Magnetic North Pole - The pole at which the magnetic force

leaves the magnet. ♣ Magnetic South Pole - The pole at which the magnetic force

re-enters the magnet. ♥ Compass needle - is a permanently suspended magnet .♥ In the presence of other magnets, the compass needle deflects

from its usual N-S position. Around a magnet is a “magnetic field”.♥ Magnetic field - is the region in space where the magnet affects another

magnet(such as compass needle) & magnetizable objects( like iron fillings).

- surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field.

♥ Magnetic lines of induction are imaginary lines which is also called “flux lines”.

♣ Flux Lines - The force pattern of a magnet - represented by lines showing direction and strength of force.

♥ In a magnetic field, the N-pole of the compass needles take the direction of the magnetic lines of induction. Outside a magnet, these lines run from the N-pole to the S-pole. They go beyond the S-pole toward the N-pole within the magnet. They form “Closed Loops”.

♥ Lines of induction are not equally distributed within the magnetic field. More lines of induction

are found at the “poles” than at points farther away.

♣ Poles - The concentration of the lines of force - the strongest magnetic point.

Magnetic field pattern of magnets w/ a) like poles b) Unlike poles

Unlike poles-flux pattern. Like poles-flux pattern.

Like poles repel. Unlike poles attract.

♥ Compass needles align themselves in a magnetic field. The N-pole of the compass needle is represented by the shaded portion.

♥ The number of lines passing through a perpendicular area reflects the “strength of the magnetic field” at that portion. The number or group of lines passing through a unit area is called “magnetic flux”(Φ). The “greater the flux per perpendicular unit area, the stronger the magnetic field”.

♥ Thus in a bar magnet, the field is strongest as the poles. This explains why more iron fillings are found than at any other point in the field. Around a magnet, the strength & direction of the magnetic field vary.

♥ The field has a “magnitude or strength” which depends on the magnetic flux per unit area.

♥ B = Φ/A

Where:

B = magnetic field Φ = magnetic flux A = perpendicular unit

areaWeber = the unit of fluxTesla = the unit of magnetic field.

♥ The direction of magnetic lines of induction is “indicated by the N-pole of a compass needle”.

♥ Magnetic field is a “vector quantity”.

Law of Magnets :

♥ “Unlike poles of magnets attract like poles repel”.