INTRODUCTION TO MAGNETISM

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WHAT IS A MAGNET?

• Magnet:• Material that can

create magnetic effects by itself

• Magnetic:• The ability to exert

forces on magnets or other magnetic materials

TYPES OF MAGNETS

•Permanent Magnet: (hard magnets)• Material that keeps its magnetic properties,

even when it is not close to other magnets.• Example: Lodestone containing magnetite

• Temporary Magnet: (soft magnets)• Acts as a magnet only as long as it is in the

magnetic field produced by a permanent magnet or an electric current.

ELEMENTS THAT CAN BE MAGNETIC:

Elements that can be magnetic

1. Fe: Ironsoft iron loses magnetism easily

2. Co: Cobaltused to harden tools

3. Ni: Nickelused to make jewelry

Other magnets:4. Compass5. Earth

PROPERTIES OF MAGNETS

1. Have lined up atoms

2. Have polarity – North and South poles

3. Cannot have only 1 pole *** magnetic poles cannot be isolated***

4. Like poles repel; Opposite poles attract

WHAT IS A MAGNETIC FIELD

• An area where the force exists; area where force is felt• Leaves north pole & enters south pole• Strongest at the poles

FIELD LINES AROUND A MAGNET

EARTH’S MAGNETIC FIELD

• Compass:• Device containing

a magnet that interacts with Earth’s magnetic field to indicate direction

ELECTROMAGNETISMHTTPS : / /WWW.YOUTUBE .COM/WATCH?V=RV4MJAF_WOWHTTPS : / /WWW.YOUTUBE .COM/WATCH?V=TXMKR69 JGBKHTTPS : / /WWW.YOUTUBE .COM/WATCH?V=NQDOYXJZ J0U

ELECTRIC CURRENT AND MAGNETISM

• In 1819, Hans Christian Oersted, a Danish physicist and chemist, and a professor, placed a compass needle near a wire through which he could make electric current flow.

• When the switch was closed, the compass needle moved just as if the wire were a magnet.

ELECTRIC CURRENT AND MAGNETISM

• Electric current is made of moving charges (electrons), which creates the magnetic field around a current-carrying wire • Magnetism is created by these moving charges

THE MAGNETIC FIELDS OF STRAIGHT WIRE

• The magnetic field lines are concentric circles with the wire at the center of the circles. • The direction of the field depends on the

direction of the current in the wire.

THE MAGNETIC FIELDS OF STRAIGHT WIRE

• The strength of the magnetic field near the wire depends on two factors:

1. The strength is directly proportional to the current, so doubling the current doubles the strength of the field.

2. The field strength is inversely proportional to the distance from the wire. (Decreasing the distance to the wire by half doubles the strength of the field.)