* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Magnetism
Van Allen radiation belt wikipedia , lookup
Skin effect wikipedia , lookup
Magnetosphere of Jupiter wikipedia , lookup
Magnetosphere of Saturn wikipedia , lookup
Electromotive force wikipedia , lookup
Maxwell's equations wikipedia , lookup
Geomagnetic storm wikipedia , lookup
Edward Sabine wikipedia , lookup
Friction-plate electromagnetic couplings wikipedia , lookup
Mathematical descriptions of the electromagnetic field wikipedia , lookup
Magnetic stripe card wikipedia , lookup
Electromagnetism wikipedia , lookup
Neutron magnetic moment wikipedia , lookup
Magnetometer wikipedia , lookup
Magnetic nanoparticles wikipedia , lookup
Magnetic monopole wikipedia , lookup
Giant magnetoresistance wikipedia , lookup
Lorentz force wikipedia , lookup
Electromagnetic field wikipedia , lookup
Earth's magnetic field wikipedia , lookup
Magnetotactic bacteria wikipedia , lookup
Magnetohydrodynamics wikipedia , lookup
Multiferroics wikipedia , lookup
Magnetoreception wikipedia , lookup
Superconducting magnet wikipedia , lookup
Magnetotellurics wikipedia , lookup
Electromagnet wikipedia , lookup
Force between magnets wikipedia , lookup
Magnetochemistry wikipedia , lookup
What is a Magnet? Magnets are made from a very small handful of chemical elements who have special magnetic properties Iron, Cobalt and Nickel are the three elements that are normally used to make magnets- all are metals close to each other on Periodic Table Some “rare earth” elements can make very powerful magnets- Neodymium is one commonly used Magnets in History Magnets named after area of Turkey called Magnesia in ancient times Strange “magic” stone that stuck to iron; regarded as curiosity by Greeks Used by Chinese as first compasses for ship navigation (shaped piece of magnetite floated in bowl of water) or on specially marked boards Suspended magnetized needle used in modern compasses What is a Magnet ctd… A magnet creates a magnetic field around it that can exert a force Magnetic forces take the form of loops that curve from one side of a magnet to the other, like a closed electric circuit No-one really knows what a magnetic field actually is- proposed to be distortions in space-time itself Magnetic Poles The loops of magnetic forces are produced by magnetic poles, one on each side of a magnet. Every magnet has both a North and South pole. Like poles repel, unlike poles attract. Magnetic Fields Magnetic fields transmit magnetic forces. Direction of the field is from N to S. Field is stronger where field lines are closer. Unit of magnetic field strength is the Tesla. What Causes a Magnetic Field? Magnetic fields are produced by moving electric charges. Electrons in atoms both orbit and “spin”. In most materials, electron spin contributes more to magnetism than electron orbital motion. Electrons are (very) tiny magnets. What Causes a Magnetic Field? Electrons with opposite spins cancel each other’s magnetic fields. Electrons with spins aligned strengthen each other’s magnetic fields. Iron, nickel, cobalt (and a few other rare earth elements) commonly have some aligned electrons. An iron atom is a (very) tiny magnet. Magnetic Domains A region in which many atoms have their magnetic fields aligned is called a magnetic domain. A typical magnet that has many domains with their atoms all aligned in the same direction creates a strong magnetic field; if there are fewer domains, the magnet is weaker How Magnets Attract A magnet near an unmagnetized piece of iron causes: Growth of aligned domains in the iron Rotation of domains to align with the magnetic field Attractive magnetic force on the iron This causes the iron to become temporarily magnetized Making a Magnet You can make a magnet by: Placing a magnetic material like iron in a strong magnetic field Stroking a magnetic material like iron with a strong magnet In both cases, the magnetic field physically “turns around” the iron atoms so they all spin in the same direction, including the spin of their electrons Electric Currents & Magnetism Since moving charges create magnetic fields, an electric current creates a magnetic field. A coil of wire can concentrate the magnetic field and create an electromagnet. Magnetism and electricity are really just different aspects of the same force- you cannot have one without the other!! Making an Electromagnet A battery and coil of wire creates a magnetic field- as the electrons move they create a “sleeve” of magnetic force around the wire You can make the electromagnet stronger in 3 ways: Increase the current (moving charges) Increase the nmber of loops in the coil Add an iron, cobalt or nickel core or else increase its size if one is already present Magnetic Forces on Charges A static electric charge does not “feel” a magnetic field. No magnetic force is exerted on it. If an electric charge moves, it generates its own magnetic field, which interacts with the original magnetic field, so: A magnetic field exerts a force on a moving electric charge. This means you can use magnetic fields to “steer” electrons in different directions This is how an old TV works- a shaped, modulated electron beam is aimed at a screen to make a desired pattern that changes and moves. This produces the picture that you see Motors An electric motor uses a magnet to exert a force on a current-carrying coil of wire. An electric motor uses brushes and an armature to reverse the flow of current so that the coil of wire can rotate 360o. One magnet repels the armature half a turn, the other attracts half a turn to make it move. This happens fast- armature spins very quickly to create mechanical motion Generators If you rotate a magnet in a coil of wire, it induces a current to flow through the wire- electromagnetic induction Used for generators, which turn mechanical movement into electric power Used in car engines to recharge a battery by reversing the chemical reaction inside the battery The Earth as a Magnet Earth itself is a huge magnet. The outer core is molten iron and nickel; spins inside the Earth and produces magnetism N and S poles do not correspond exactly to the geographic poles. The discrepancy is called magnetic declination. Strength of Earth’s field varies with time. N/S Poles have switched in the past. The Earth as a Magnet The Earth’s magnetic field is powerful enough to deflect high energy particles streaming out from the Sun towards us (solar wind) Interaction of solar wind with magnetic field produces light in a hazy, beautifully colored display Called Aurora Borealis- Northern Lights