Download
slide1 n.
Skip this Video
Loading SlideShow in 5 Seconds..
Magnetism PowerPoint Presentation

Magnetism

281 Vues Download Presentation
Télécharger la présentation

Magnetism

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Magnetism

  2. Strange Stones • A young Shepard named Magnes discovered Magnetism when iron nails of his sandal stuck to a stone.

  3. History of Magnets • Over 2,000 years ago, Greeks discovered a mineral that attracted things made of iron • Found in a part of Turkey called Magnesia, so they called it Magnetite

  4. Magnets have been known for centuries. The Chinese and Greeks knew about the “magical” properties of magnets. The ancient Greeks used a stone substance called “magnetite.” They discovered that the stone always pointed in the same direction. Later, stones of magnetite called “lodestones” were used in navigation.

  5. What is a Magnet? • A magnet is any material that attracts iron or things made of iron.

  6. What is Magnetism? Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons.

  7. What are the atoms inside of a magnet doing? • As negatively charged electrons move around, they make, or induce, a magnetic field. • In most material the magnetic field of individual atoms cancel each other. • In some materials the north and south poles line up in a domain (place where groups of atoms are found). • If most of the domains in an object align they can combine to make an entire object magnetic.

  8. Atoms themselves have magnetic properties due to the spin of the atom’s electrons. • Domains: Groups of atoms join so that their magnetic fields line up • These areas of atoms are called “domains”

  9. What does the inside of a magnet look like? Inside a non-magnetic object Inside a magnetic object

  10. An unmagnetized substance looks like this…

  11. While a magnetized substance looks like this…

  12. Kinds of magnets Temporary Magnets Permanent Magnets • Difficult to magnetize and keep their magnetic properties longer than temporary magnets. • Some permanent magnets are made with alnico-an alloy made up of aluminum, nickel, cobalt, and iron. • Made from materials that are easy to magnetize, but lose their magnetism easily. • Soft iron is iron that has not been mixed with any other materials and can be made into temporary magnets • The paper clip and nail in the mini-lab were temporary magnets.

  13. Can magnets be demagnetized? • When a magnet’s domains move, the magnet is demagnetized and loses its magnetic properties. • This can be done by: • Dropping a magnet • Hitting it too hard • Putting a magnet in a strong magnetic field that is opposite to its own • Increasing the magnet’s temperature-with a higher temperature, atoms vibrate faster and the atoms in the domains may no longer line up

  14. Magnetic Properties • Magnetic Poles • Magnetic Forces • Magnetic Fields

  15. PROPERTIES OF A MAGNET: POLES The ends of a magnet are where the magnetic effect is the strongest. These are called “poles.” Each magnet has 2 poles – 1 north, 1 south.

  16. Attraction/Repulsion • Example of Attraction: • Examples of Repulsion:

  17. Like repels like… Opposites attract!

  18. Poles of a magnet always Come in pairs!

  19. If you cut a magnet in half, you get 2 magnets! Why? A magnet has poles because its domains are lined up, and each domain is like a very tiny magnet with a north and south pole, so even the smallest pieces of a magnet have a north and south pole.

  20. Magnetic Force • The force around a magnet that attracts or repels.

  21. Magnetic fields • Region around a magnet in which magnetic forces can act • Shape is shown with lines drawn from the north pole of the magnet to the south pole, called magnetic field lines • The closer together the magnetic field lines are the stronger the magnetic force is • What part of the magnet has the strongest magnetic force? How can you tell? • AT THE POLES – magnetic field lines are closest together!

  22. Magnetic Field Interactions Two Opposite Poles Two Like Poles

  23. William Gilbert, an English physician, first proposed in 1600 that the earth itself is a magnet, and he predicted that the Earth would be found to have magnetic poles.

  24. The Earth is a magnet: It exerts magnetic forces and is surrounded by a magnetic field that is strongest near the North and South magnetic poles Geographic North Pole Magnetic South Pole Magnetic North Pole Geographic South Pole

  25. The earth as a magnet. • Scientists think that the earth’s magnetic field is made by the movement of electric charges in the Earth’s liquid outer core, which is made out of iron and nickel. • When the Earth rotates, the liquid in the core flows • When the liquid flows, electric charges move, which makes a magnetic field

  26. Magnetic North Pole Sometimes, the Earth’s magnetic poles flip. This happens every half-million years or so. Magnetic South Pole

  27. Using a compass • How does a compass work? • The compass needle points north because its north pole is attracted to the earth’s magnetic south pole. • What does this mean then? • The earth has a very strong magnetic field

  28. The sun has a magnetic field, too. It extends far above the sun’s surface. Other planets in the solar system also have these magnetic fields

  29. The solar wind is constantly bombarding the Earth’s magnetic field. Sometimes these charged particles penetrate that field. These particles are found in two large regions known as the Van Allen Belts.

  30. The Earth’s magnetic field extends far into space. It is called the “magnetosphere.” When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called…

  31. The Aurora Borealis in the Northern Hemisphere And the Aurora Australis in the Southern Hemisphere

  32. Video