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Chapter 8. Magnetism & Its Uses. Sec 1: Magnetism. Over 2000 years ago Greeks first discovered magnetism in a mineral they called magnetic. Magnetism —properties and interactions with magnets Magnets attract metal objects. Magnetic Force & Magnetic Fields.

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chapter 8

Chapter 8

Magnetism & Its Uses

sec 1 magnetism
Sec 1: Magnetism
  • Over 2000 years ago Greeks first discovered magnetism in a mineral they called magnetic.
  • Magnetism—properties and interactions with magnets
  • Magnets attract metal objects.
magnetic force magnetic fields
Magnetic Force &Magnetic Fields
  • Magnetic force—the interaction between magnets.
    • The strength of this force increases as magnets move closer together.
  • Magnetic field—the area surrounding a magnet that exerts the magnetic force.
    • Iron and other magnets react to the magnetic force when placed in the magnetic field.
    • Magnetic field can be represented by lines of force, or magnetic field lines.
magnetic poles
Magnetic Poles
  • Magnetic field lines are closest to each other at the ends of the bar magnet
  • These are magnetic poles—where the magnetic force exerted by the magnet is the strongest.
  • All magnets have a north and south pole.
    • Bar magnet—poles are at opposite ends
    • Horseshoe magnet—the poles are the two ends (like a bent bar magnet)
interacting magnets
Interacting Magnets
  • Magnets either attract or repel each other.
  • When 2 north poles or 2 south poles come close, you can feel a force preventing the magnets from touching.
  • North poles always attract south poles.
  • When 2 magnets come close, their magnetic fields combine.
a compass needle
A Compass Needle
  • A compass contains a needle (a small bar magnet) that is free to rotate.
  • When placed near a bar magnet, the north pole of the needle will turn towards the south pole of the magnet.
  • A compass needle will point towards the North Pole of Earth.
  • Earth acts as like a gigantic bar magnet, and its magnetic field extends into space.
earth s magnetic poles
Earth’s Magnetic Poles
  • The north pole of a magnet is the end of the magnet that points towards geographic north.
  • The north pole of a magnet attracts a south magnetic pole.
  • Earth’s south magnetic pole is near the geographic north pole.
    • It is located in Canada about 1500km from the geographic north pole.
magnetic materials
Magnetic Materials
  • A magnet will not attract all metal objects.
  • Only a few elements can be made into permanent magnets
    • Iron, cobalt, & nickel
  • Objects made from these metals are not always magnetic.
    • Put an iron nail next to a refrigerator, let go, and it falls to the floor.
  • You can make these metals behave like magnets temporarily.
permanent magnets
Permanent Magnets
  • Iron, cobalt, or nickel can be made into permanent magnets by placing them in a strong magnetic field.
  • This creates a magnetic field inside the material
  • It can retain magnetic properties for a long time.
  • Permanent magnets can lose their magnetism if heated or dropped.
  • When a magnet is broken, each piece still has a north and south pole!
    • Even the smallest pieces of a magnet have a north and south pole.
sec 2 electricity magnetism
Sec 2: Electricity & Magnetism
  • Electric currents cause magnetic fields.
  • The magnetic field around a current-carrying wire forms a circular pattern around the wire.
  • The strength of the field depends on the amount of current flowing in the wire.
  • Electromagnet—a temporary magnet made by placing a piece of iron inside a current-carrying coil of wire.
    • When current flows through the loop of wire, magnetic field lines form around the wire.
    • The more loops of wire, the stronger the magnetic field.
properties of electromagnets
Properties of Electromagnets
  • Electromagnets are temporary because they are only magnetic when current is flowing through the wire.
  • Electromagnets convert electrical energy into mechanical energy to do work.
stereo speakers
Stereo Speakers
  • The mechanical energy produced from an electromagnet vibrates parts of a speaker to produce sound.
electric motors
Electric Motors
  • Electric motor—a device that changes electrical energy into mechanical energy.
    • Contains an electromagnet that is free to rotate between poles of a permanent magnet connected to the battery.
    • When current flows through the electromagnet, a magnetic field is produced in the coil.