R Ch 36 Magnetism pg 1 Text Qs pg 575 RQ 1, 2, 4, 5, 7-9,12,13,19
R Ch 36 Magnetism pg 2 Magnets are essential for modern life, they are used in generators, motors, lights etc. Originally called loadstones they were found naturally in Magnesia, Greece about 2,000 yrs ago They contain a form of iron called Magnetite Magnetism & electricity were linked in 1820 by Hans Oersted while playing with a compass and a current carrying wire
R Ch 36.1 Magnetic Poles pg 3 Magnets have these properties; 1) are a no touch force 2) attract or repel 3) their effect follows the inverse square law for distance 4) Magnetic force = mag. Pole strength x mag. Pole strength / d2 5) Magnets always have two poles ( N & S )
R Ch 36.2 Magnetic Fields pg 4 The space around a magnet is filled with a magnetic force field 1) The direction of the field is N -> S 2) The field is strongest at the poles 3) Lines can be drawn to represent the field & the closer the lines the stronger the field
R Ch 36.3 The nature of the Magnetic Field pg 5 Magnetism is produced by the motion of an electric charge, magnets get their moving charges from the electrons moving around inside
R Ch 36.3 The nature of the Magnetic Field pg 6 Remember that electrons 1) orbit the nucleus 2) spin on their axis, stronger than orbit
When the spin & orbit match-up, the magnetic fields add When the spin & orbit are opposite they cancel R Ch 36.3 The nature of the Magnetic Field pg 7
R Ch 36.3 The nature of the Magnetic Field pg 8 Electron usually exist in pairs When electrons are paired up, their spins are opposite they cancel The canceling effects of the various spins & orbits are the reason most materials are not magnetic
R Ch 36.3 The nature of the Magnetic Field pg 9 Iron, cobalt & nickel all are magnetic because they have single electrons with spin that is not canceled by a partner electron Iron is the strongest with four unpaired electrons, cobalt next with three unpaired electrons, nickel weakest with two unpaired electrons
R Ch 36.3 The nature of the Magnetic Field pg 10 Iron, cobalt & nickel are mixed with aluminum (for weight) to make common magnets
R Ch 36.4Magnetic Domains pg 11 Magnetic domains are clusters of atoms aligned with their N & S poles all pointed in the same direction.
R Ch 36.4 Magnetic Domains pg 12 Permanent magnets are made by placing iron in a strong magnetic field and; 1) tapping the iron to help the domains align 2) sliding a magnet along the iron to the domains align Permanent magnets are destroyed by 1) heating 2) dropping the magnet because it knocks the domains out of alignment
R Ch 36.5 Electric Currents & Magnetic Fields pg 13 Electric current produces a magnetic field because it is the movement of charges. Looping wire around a piece of Iron will create an electromagnet that can be switched off and on.
R Ch 36.5 Electric Currents & Magnetic Fields pg 14 MRI (magnetic resonance imaging) machines do this by using a strong magnetic field to flip all of your electrons up and then letting them flip back to their natural position. When your electrons flip back they move giving off a weak magnetic signal that the machine detects and uses to construct an image of your insides
R Ch 36.6 Magnetic Forces on Moving Charge Particles pg 15 Moving charged Particles behave weirdly in a magnetic field; 1) static charge & static field = no interaction 2) charge & field not moving relative to each other = no interaction 3) Charge & magnetic field moving at right angles to each other = creating a force perpendicular to the magnet motion & the charge motion
R Ch 36.6 Magnetic Forces on Moving Charge Particles pg 16 This right angle motion is how TV sets bend the electrons that make the picture
R Ch 36.7 Magnetic Forces on Current Carrying Wires pg 17 Wires also feel the force of a magnet field if the current is moving through the wire and the wire is at a right angle to the magnetic field. This is how motors, generators, speakers & microphones work
R Ch 36.8 Meters to Motors pg 18 Voltmeter – measures volts Ammeter – measures amps (current) Electric motors changed the world by replacing human & animal power. Electric motors spin because a permanent magnet puts a force on an electromagnet by switching the poles to keep like poles together so they always repel and keep moving
R Ch 36.9 The Earth’s Magnetic Field pg 19 The earth has two North poles; 1) Magnetic north (where a compass points) near Hudson’s Bay in Canada. It moves a little every year. 2) True north is at the north pole. In Chicago magnetic north & true north line up. The magnetic field is not perfectly understood but it caused by the magma moving around inside the earth
R Ch 36.9 The Earth’s Magnetic Field pg 20 Even weirder and not understood; 1) the earth’s magnetic field has reversed and the poles switched places. 2) the magnetic field has switched off for long periods and compasses didn’t work
R Ch 36.9 The Earth’s Magnetic Field pg 21 The average time of the magnetic reversals is every one million years and the time is about up so the next switch may be soon. The earth’s magnetic field has decreased 5% in the last 100 yrs. At this rate magnetic field will change in 2,000 yrs.