* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download L 28 Electricity and Magnetism
Maxwell's equations wikipedia , lookup
Magnetosphere of Jupiter wikipedia , lookup
Mathematical descriptions of the electromagnetic field wikipedia , lookup
Magnetosphere of Saturn wikipedia , lookup
Lorentz force wikipedia , lookup
Magnetic stripe card wikipedia , lookup
Friction-plate electromagnetic couplings wikipedia , lookup
Edward Sabine wikipedia , lookup
Electromagnetism wikipedia , lookup
Giant magnetoresistance wikipedia , lookup
Neutron magnetic moment wikipedia , lookup
Geomagnetic storm wikipedia , lookup
Magnetometer wikipedia , lookup
Magnetic nanoparticles wikipedia , lookup
Magnetic field wikipedia , lookup
Magnetic monopole wikipedia , lookup
Van Allen radiation belt wikipedia , lookup
Electromagnetic field wikipedia , lookup
Magnetotactic bacteria wikipedia , lookup
Earth's magnetic field wikipedia , lookup
Multiferroics wikipedia , lookup
Magnetohydrodynamics wikipedia , lookup
Magnetoreception wikipedia , lookup
Magnetochemistry wikipedia , lookup
Electromagnet wikipedia , lookup
Magnetotellurics wikipedia , lookup
Superconducting magnet wikipedia , lookup
Force between magnets wikipedia , lookup
L 28 Electricity and Magnetism [5] Magnetism • two sources of magnetism • permanent magnets • electromagnets Why are magnets magnets? • the earth’s magnetic field magnetism magnetic forces applications • how does a compass work • the north pole is really a south pole! • Van Allen radiation belts 2 1 Permanent magnetism • certain minerals (loadstone) are naturally magnetic • a piece of loadstone will attract bits of iron • a magnet produces a magnetic field in the space around it, just like the Sun produces a gravitational field that holds the planets in their orbits • the magnetic field can be visualized with iron filings Bar Magnet Permanent magnets • Are made from alloys of some of the rare earth elements like neodymium and samarium • Always have a north and a south pole • like poles repel and unlike poles attract • if you break a magnet in half you get 2 magnets S N S NN 3 Electromagnet 4 Homemade magnets COIL Nail Duracell + • If you pass current through a loop of wire you get a magnet Î Oersted’s discovery • Î currents make magnetic fields (Ampere’s Law) 5 You can think of the nail as a collection of little magnets that are randomly aligned. The magnetic field of the coil aligns these little magnets giving a larger field than that of the coil alone. We say that the nail becomes “magnetized”, but the effect is not permanent. 6 1 N S N S N S N S S N N S N S N S N S S N S N S N S atomic magnets N S N S N S N S SOUTH MAGNETIZED NORTH N S N S N S S N S PARTIALLY MAGNETIZED N N N S UNMAGNETIZED N S Magnetic materials • some materials are naturally magnetic or can be magnetized and retain their magnetism Æ ferromagnetic materials • other materials (iron) can be magnetized temporarily by placing them near magnets • some materials have essentially no magnetic properties Æ copper, aluminum, plastics... • heat can destroy magnetism 7 8 Acnn c tiv a te CNN Report Dec. 12, 2003 The earth is a big magnet • The earth’s north geographic pole is the south pole of a big magnet. • A compass needle is attracted to the earth’s north geographic pole • The earth’s magnetism is the magnetic north pole is due to currents flowing in inclined about 14° from the its molten core (not geographic north pole, or entirely understood!) by about 600 miles. Slight chance of flipping magnetic poles The strength of the earth’s magnetic field had decreased10% over the last 150 years. At this rate, the field will disappear altogether in 1,500 to 2,000 years. North time South 9 Sun – Earth Connection: space weather 10 Particles stay on the magnetic field lines earth electron that originated on the sun Æ part of the solar wind. solar eruption SUN Report: Earth's magnetic field fading The earth’s magnetic field traps charged particles. solar eruption Northern Lights 11 During periods of intense solar activity, satellites can be at risk. 12 2 Van Allen Radiation Belts Magnetic forces • magnetic fields can cause charges to turn around. 13 14 Magnetic forces on wires Magnetic deflection of electrons in a TV tube. N 15 Forces on parallel wires S Wire pushed OUT N S Wire pulled IN 16 Applications Magnets are not just for holding things on the refrigerator! Opposites repel Likes attract 17 18 3 The electric motor Magnets make speakers work The force between the permanent magnet and the voice coil moves the speaker cone When a current is present in a coil, it experiences a torque and rotates. 19 MAGLEV Trains 20 Magnetic tape recording 21 22 4