* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download L 28 Electricity and Magnetism [5]
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
Electromagnetism wikipedia , lookup
Edward Sabine wikipedia , lookup
Friction-plate electromagnetic couplings wikipedia , lookup
Neutron magnetic moment wikipedia , lookup
Giant magnetoresistance wikipedia , lookup
Magnetometer wikipedia , lookup
Geomagnetic storm wikipedia , lookup
Magnetic field wikipedia , lookup
Magnetic monopole wikipedia , lookup
Electromagnetic field wikipedia , lookup
Van Allen radiation belt 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] Why are magnets magnets? magnetism magnetic forces applications 1 Magnetism • two sources of magnetism • permanent magnets • electromagnets • the earth’s magnetic field • how does a compass work • the north pole is really a south pole! • Van Allen radiation belts 2 Permanent magnetism • certain minerals (magnetite, Fe3O4) 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 has a gravitational field that holds the planets in their orbits • the magnetic field can be visualized with iron filings 3 Earth’s g-field Solenoidal Coil 4 Permanent magnets • Are made from alloys of some of the rare earth elements like neodymium and samarium and cobalt. • 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 cannot have just a north or just a south pole S NS NN 5 Bar Magnet Electromagnet • If you pass current through a loop of wire you get a magnet Oersted discovered this • Ampere figured out the formula relating currents to magnetic fields (Ampere’s Law) 6 Homemade magnets COIL Iron nail Duracell + 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. 7 UNMAGNETIZED atomic magnets N S N S N S N S N S N S N S N S SOUTH MAGNETIZED NORTH PARTIALLY MAGNETIZED 8 Magnetic materials • some materials are naturally magnetic or can be magnetized and retain their magnetism ferromagnetic materials • other materials (iron) can be magnetized temporarily by placing them near magnets • some materials have essentially no magnetic properties copper, aluminum, plastics... • heat can destroy magnetism (Curie effect) 9 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. 10 Activate cnn CNN Report Dec. 12, 2003 Report: Earth's magnetic field fading 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 11 Sun – Earth Connection: space weather earth solar eruption SUN solar eruption Northern Lights 12 Solar eruptions 13 Particles stay on the magnetic field lines electron that originated on the sun part of the solar wind. The earth’s magnetic field traps charged particles. During periods of intense solar activity, satellites can be at risk. 14 Van Allen Radiation Belts 15 Magnetic forces • magnetic fields can cause charges to turn around. 16 Magnetic deflection of electrons in a TV tube. 17 Magnetic forces on wires N S Wire pushed OUT N Wire pulled IN S 18 Forces on parallel wires Opposites repel Likes attract 19 Applications Magnets are not just for holding things on the refrigerator! 20 The electric motor When a current is present in a coil, it experiences a torque and rotates. 21 Magnets make speakers work The force between the permanent magnet and the voice coil moves the speaker cone 22 MAGLEV Trains 23 Magnetic tape recording 24