Properties of magnets Magnet- material that can exert forces on magnets or other magnetic materials, like iron and steel. Poles- all magnets have 2- North and south Permanent magnets- keep their magnetic properties- bar, horseshoe, round..called “hard magnets.”- strongest: nickel, cobalt or neodymium. Temporary magnets- lose their magnetism easily. Called “soft magnets” Force of Attraction- opp. Poles( N and S) Force of Repulsion- like poles (N,N, S,S) repel. At this pt. all magnets are dipoles(2 poles), and no monopole(1 pole) exists ! Magnets can exert their forces even thru insulating materials like wood, plastic, and glass if they are strong enough. Conducting materials like iron and steel can block or change the mag. forces. USES OF MAGNETS: •junkyards, weather stripping on doors, zippers, latches, cabinet and fridge doors, handbags, etc. •MAGNETIC FIELD: area around a magnet that exerts a force. ( a force field) •Magnetic field lines– represent the mag. Field, and always go from N pole towards the S pole. The closer the lines, the stronger the force. ferromagnets Magnets made of iron, nickel or cobalt with very strong mag. Properties. Magnetic domains- millions of atoms align themselves with other atoms in groups all facing in the same direction. If a magnet is near a paperclip, the domains in the paperclip will realign with the magnet until the magnet is removed. SOURCE OF MAGNETISM ELECTROMAGNETS- coil of wire wrapped around an iron core, connected to a source of electricity-like a battery—creates a magnet. N and S poles are at each end of the coil..You can switch the poles by switching the direction of the electricity flow. EM can be much stronger than permanent magnets, b/c they can use large currents. Uses: toasters, doorbells, watches, clocks, Where is the north and south pole? Right-Hand Rule If the fingers of your RIGHT hand curl in the direction of the current, your thumb points toward the north pole. •Factors affecting electromagnets: make them stronger: a) add more turns of wire ( this increases the current over and over) b) increase the current ( more batteries) If you dbl. the batteries, you dbl .The current, and the magnet’ strength. However, more wire makes more heat c) Increase the iron core— With an EM, you can turn a switch on and off, and have it work– our doors for fire drills stay open with an EM! SO, MAGNETISM COMES FROM ELECTRIC CURRENTS! Some materials, like lead and diamonds are not magnetic at all, whereas aluminum can be a weak magnet, but is often nonmagnetic, b/c the atoms are not aligned naturally. What destroys magnets? Increasing temperature can ruin the domains Dropping the magnets Changing the domains alignment somehow • Compass needles: As early as 500 B.C., people were using Lodestone(magnetite) as a compass. oCompass needle- free moving magnet. It stops spinning when it is lined up with the magnetic field present. o the needle lines up w/ local mag. Field, w/ N pole of compass attracted to S pole of mag. Field . o The N pole of a compass actually points to the Earth’s SOUTH MAGNETIC POLE, which is near the NORTH GEOGRAPHIC POLE!!! oThe S pole of a compass points to the Earth’s NORTH MAGNETIC POLE, near the S G Pole. A compass does NOT pt. directly to the geo. N pole, but near it. It will always be slightly E or W of the G N Pole. ( mag. S. P is about 600 miles( 1000 km) from GNP). Magnetic Declination. The difference between the direction the needle points, and True G North, is called You can measure the “angle of declination.”– PAGE 371 OF TEXT—LOOK TOGETHER !! INTERESTING FACTS: GAUSS-unit to measure the strength of a mag. Field. Mag. Field of Earth is weak compared to a classroom magnet. The poles of our Earth have reversed about every 500,000 yrs. Last one was about 750,000 yrs. Ago, so we are due!! Location of our mag. Poles is always changing. Chapter 16.1 Objectives and Vocabulary Recognize that magnetic poles always exits in pairs. Decide whether two magnetic poles will attract or repel. Describe the magnetic field and forces around a permanent magnet. magnetic permanent magnet magnetic poles magnetic field magnetic field line The earth’s magnetic field The earth has an imaginary bar magnet going thru its’ core. The mag. Field of earth would look just like the field around the bar magnet; But, the solar winds from the sun, change its shape slightly. WILLIAM GILBERT: 1600--discovered that the E. has a magnetic field around it. The E. core is mostly iron and nickel, creating the mag. Field. Solar winds- from the sun blow on the E. mag. Field, creating a “tail.”-reshaping the Mag. Field of Earth -- called the Magnetosphere. These winds push radioactive particles toward the E. •Van Allen Radiation Belts–“trap” most of the rad. particles from the sun, keeping them from harming us. •Any particles that escape the belts, get attracted to the N and S poles of the Earth, and react with gases in the atmosphere, creating Auroras. Now you draw it with me: PICTURES OF AURORAS Auroras- charged part. From Sun react with gases in the atmosphere at the northern and S. poles, and create brilliant light shows. Northern Lights- A. Borealis Southern lights- A. Australis FACTS TO KNOW: Sunspots: come in pairs, with poles, and are dark circular areas that are cooler, and magnetic. Every 11 yrs. the annual # of sunspots varies, and the sun’s mag. Poles reverse. Jupiter and Saturn also have mag. Fields.