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?What is a force of attraction or repulsion between like and unlike poles? –Magnetism Where is this force the strongest?Where is this force the strongest? –The poles What is the Iron Triad?What is the Iron Triad? –Iron, Cobalt, Nickel; only elements to form permanent magnets What are groups of atoms with aligned magnetic poles?What are groups of atoms with aligned magnetic poles? –Magnetic Domains How can a magnet loose some of its magnetic properties?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 current- carrying 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

1. Step-up Increases voltage More coils in secondary coil 2. Step-down Decreases voltage More coils in primary coil Transformers

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 switchReversing switch CommutatorCommutator Compasses point hereCompasses point here Magnetic northMagnetic north A transformer that increases voltageA transformer that increases voltage Step-up transformerStep-up transformer Material which has no electrical resistanceMaterial which has no electrical resistance SuperconductorSuperconductor STUDY VOCABULARY!!!!!STUDY VOCABULARY!!!!!