2Properties of MagnetsYou can investigate the properties of magnets by bringing two magnets together.The ends of the magnets attract each other and stick together.The ends of the magnets repel each other and the magnets move apart.
3Magnetic PolesMagnetic poles: One of the two ends of a magnet where magnetic force is strongest.When a magnet spins freely it always points the same directionThe end of a magnet that points north is called the north pole, and the end pointing south is the south pole.All magnets have a north and a south pole.
4When two north poles or two south poles are brought near each other, they repel. But if the north and south magnetic poles are brought near each other they will attract.Magnetic poles can’t be separated from each other.If you break a magnet in half each piece is still a magnet with a north and south pole.
5Magnetic Field: The area of magnetic force surrounding a magnet. The magnetic fields is strongest at the poles of a magnet, but exists around the entire magnet.Magnetic field lines exists from one pole to the other.
6The number of field lines in any given region indicates the relative strength of the field Although the magnetic field is invisible you can see its effect around a magnet by placing a piece of paper on top of a magnet and then sprinkling iron fillings over the paperIf you were to place a magnetic material, such as iron, near the magnet it would be most attracted to either the north or south pole
10Magnetic MaterialsThe electrons of all atoms spin as they move about the nucleusA spinning electron produces a magnetic field with both a north and south poleIn most materials, the magnetic fields of individual atoms cancel each other, so the materials aren’t magneticIn certain materials this isn’t the case
11The poles line up in the same direction in microscopic magnetic regions, called magnetic domains When all the domains are arranged with their poles in the same direction, the iron bar becomes a permanent magnetWhen the domains are arranged randomly, the iron bar is not magnetized
14Earth As A MagnetIf you hang a magnet by a string, the north seeking pole will always point north because the earth itself is a huge magnetAn instrument that takes advantage of the earths magnetic field is the compassA compass has a magnetized needle in it that turns freelyThe north and south pole of the earth’s axis are referred to as geographic north pole sometimes called true north
16Evidence suggests that the earths magnetic field is caused by the movement of molten metals near the earths coreMeasurements show that the earths magnetic poles change position over timeChanges in the flow of the molten metals inside the earth may cause the magnetic poles to move
17Magnetic EffectsThe most visible effect of the earths magnetic field is a colorful light display, called an auroraAn aurora hangs like a curtain of light stretching over the polar regions of the earthCollisions between the charged particles and other particles in the upper atmosphere create glowing lights
21The color of aurora depends on the kind of atoms in the atmosphere Magnetic storms interfere with compass needles and radio and television waves.Magnetic storms occur when solar flares produce charged particles that become trapped in the earth’s magnetic field.
22Earth’s magnetic field affects living things. They have magnetic particles inside their bodiesThese particles help organisms using the magnetic field to find their way.
23ElectromagnetismIn 1820, Christian Oersted, a Danish physicist made an observation that when a compass was brought near electric current, the compass needle no longer pointed north. It turned 90 degrees.The compass needle turned in the opposite direction when he reversed the current.
24He hypothesized that when an electric current flowed through it, the wire acted like a magnet. Somehow electricity could produce magnetism.
27ElectromagnetsOersted’s discovery is responsible for the invention of new tools based on the principles of electromagnetism.Electromagnet: a magnet made of a soft-iron core surrounded by a coil of wire through which an electric current passed.The strength depends on the number of turns in the coil, the amount of current, and the size of the iron core.
29The greater number of turns a coil has, the stronger the magnetic field can produce. The greater the size of the soft-iron core, the stronger the magnet is.When a magnet is turned on an electric current flows through the wire coil, creating a magnetic field around the coil.The magnetic domains in the soft-iron core align with the magnetic field of the coil.
30The soft-iron core becomes magnetized. One end of the soft-iron core is a north pole, and the other end is the south pole.The magnetic field of the magnetized soft-iron core combines with the magnetic field of the wire coil. The combined magnetic fields create a very strong magnet.
31Pure iron is referred to as soft iron. An electromagnet exerts a magnetic force that can make things move.
32Electric MotorsAn electromagnet, called an armature, is placed in the magnetic field of permanent magnet.When current flows through the electromagnet, its poles repel the like poles of the permanent magnets.When the direction of the current changes, the poles on the electromagnet reverse, and the electromagnet spins
34The commutator is split metal ring that acts as as a switch The communicator reverses the current in the electromagnetElectric current enters the electromagnet through brushes that touch the spinning communtator rings
36Current MetersThe response of magnetic forces between an electromagnet and a permanent magnet is used in various kinds of meters
37Current MetersThe two springs connected to the rod through the electromagnet control the pointer of the galvanometerWhen an electric current passes the electromagnet, the poles of the electromagnet respond to the poles of the permanent magnet
38Electromagnetic induction: The process of inducing a current by moving a magnetic field through a wire coil without touching it.This occurs any time motion takes place between the wire and the magnetic field.A weak current is produced when the movement of the wire is slow.A strong current is produced when the movement is fast.
39GeneratorsDevices for converting mechanical energy to electrical energy.Spin a coil of wire through a magnetic fieldWill make a current flow through wireMake alternating current as the go past the different poles of the magnet.
41Transformer Changes the voltage of alternating current Power comes at high voltage because the power company loses less energy.A step-down transformer lowers the voltage to 120V or 240V for your houseUses two coils of wire and a soft iron corePrimary coil inSecondary coil out
42Step-down Transformer Has more coils on primary than secondaryDecreases voltage
43Step-Up Transformer Has more coils on secondary than primary Increases voltage
44Transformers As the alternating current changes direction So does the magnetic fieldWhich makes the alternating current in the other coil