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Ch 21-Magnetism Magnetism • a property of matter in which there is a force of attraction or repulsion between like and unlike poles Magnetic Poles • force is strongest at the magnetic poles: North & South • Like poles repel, unlike attract •Force of attraction decreases as distance between magnets increases If a bar magnet is suspended so it turns freely (like a compass), it will point magnetic N Permanent Magnets • made from iron-Fe,cobalt-Co,or nickel-Ni (aka the IRON TRIAD) • retain magnetic properties for a long time Temporary Magnets • happens when object is near or is touching a magnet • lose magnetic properties soon after they are separated from a magnet Magnetic field • area around the magnet where forces act Magnetic domains • groups of atoms w/ aligned magnetic poles • magnets can lose some magnetic properties if dropped or heated “drop it like it’s hot” •if a magnets breaks, you have lots of little magnets Star questions • What is a force of attraction or repulsion between like and unlike poles? – Magnetism • Where is this force the strongest? – The poles • What is the Iron Triad? – Iron, Cobalt, Nickel; only elements to form permanent magnets • What are groups of atoms with aligned magnetic poles? – Magnetic Domains • How can a magnet loose some of its magnetic properties? – Heat it or Drop it Uses of Magnetic fields • Hans Christian Oersted – observed that a current moving through a wire moved the needle on a nearby compass; moving electric charges create a magnetic field. Uses of Magnetic fields Solenoid – coil of currentcarrying wire that produces a magnetic field Uses of Magnetic fields • Electromagnet – strong, temporary magnet made by inserting an iron core into a wire coil & passing an electric current through the coil. Strength of electromagnet can be increased by: • inserting iron core • adding more turns to the wire • increasing the amount of current Electromagnetic Devices • Electromagnets change electrical energy to mechanical energy Motor using an electromagnet to turn an axle •Commutator – reversing switch Electromagnetic Devices • Galvanometer – detects electric current, using a solenoid Generating Electric Current • Michael Faraday discovered electromagnetic induction; according to his law, a voltage is induced in a conductor by a changing magnetic field Electromagnetic induction Generating Electric Current • Generators – produce electric current by rotating a loop of wire in a magnetic field. Generators • Mechanical energy produces electrical energy FORCE • Moving electric charges produce magnetic force • Moving magnets produce electric force Two types of generators 1. Direct current (DC) - current flows in one direction, example is dry cell batteries 2. Alternating current (AC) current reverses direction in a regular pattern Transformers 1. Step-up • Increases voltage • More coils in secondary coil 2. Step-down • Decreases voltage • More coils in primary coil Transformers Voltage converters like in USA, Europe, Asia, Africa, Australia Superconductors • Material that has no electrical resistance • Occurs at OK Advantages • current flows indefinitely • eliminates electrical waste Disadvantages • brittle, hard to shape into wires • need to be cold in order for it to work LAST Star questions • • • • • • • • • Reversing switch Commutator Compasses point here Magnetic north A transformer that increases voltage Step-up transformer Material which has no electrical resistance Superconductor STUDY VOCABULARY!!!!!