Ch. 8 - Magnetism

Ch. 8 - Magnetism

I. Characteristics of Magnets Magnetism Magnetic poles Magnetic field Magnetic domain

A. MagnetismMagnetism

force of attraction or repulsion between unlike or like poles

due to the arrangement of electrons

closely related to electricity

B. Magnetic PolesMagnetic Poles

like poles repel

unlike poles attract

a broken magnet creates new poles

C. Magnetic FieldMagnetic Field

area around a magnet where magnetic forces act

field lines show direction of field (NS)

D. Magnetic DomainMagnetic Domain

groups of atoms with aligned magnetic poles

in a magnetized object, domains are all aligned

domain

Strength of magnets and magnetic fields

Attraction and repulsion of magnets increases as they get closer to one another

…and decreases as they get farther apart.

Magnetic fields are strongest at the poles.

Permanent magnetsNot all metals can become magnetic.

Aluminum foil – for instance, does not. Iron, cobalt and nickel are the only metals

that can become magnets. Permanent magnets are created when these

metals are placed within a strong magnetic field.

Loss of magnetismPermanent magnets can lose their

magnetism when heated …or when they suffer a large impact.

Ch. 8 - Magnetism

Ch. 8 - Magnetism

II. Uses of Magnetic Fields Electromagnet Speaker Motor

A. ElectromagnetElectromagnet

strong, temporary magnet formed when current is passed through a coil of wire surrounding an iron core

acts like a bar magnet when current is on

B. SpeakerSpeaker

electrical energy mechanical energy

wire coil moves back & forth as its magnetic field interacts with a fixed magnet

forced vibration causes the cone to move sound

C. MotorMotor

electrical energy mechanical energy

electromagnet rotates between the poles of a fixed magnet

commutator reverses the poles of the e’magnet

C. Motor

brushes & wires to battery field magnet

armature & commutatorassembled motor

D. GalvanometersDevices that use electromagnets to measure

electric current (ex. sensors or gauges in your car.

Ch. 8 - Magnetism

Ch. 8 - Magnetism

III. Producing Electric Current

Electromagnetic Induction Electric Generator DC & AC Transformer

A. Electromagnetic InductionElectromagnetic Induction

producing a current by moving a wire through a magnetic field

some microphones work just like mini-speakers in reverse

sound waves cause coil to move current

Dynamic Microphone

Coil

B. Electric GeneratorElectric Generator

mechanical energy electrical energy

armature is rotated between magnet poles

magnetic field induces a current in the wire coil

MOTORGENERATOR

B. Electric Generator Hydroelectric Dam

PE of lake water is converted to KE

mechanical KE turns the generator shaft which creates electrical energy

C. DC & ACDirect Current (DC)

current flows in one direction dry cells

Alternating Current (AC) current reverses its direction

at regular intervals electrical outlets

D. TransformerTransformer

increases or decreases AC voltage primary coil AC produces a magnetic field that

induces AC in the secondary coil voltage ratio = ratio of turns in each coil

D. TransformerStep-up Transformer

increases the voltage more turns power plants

Step-down Transformer decreases the voltage fewer turns household appliances

(hairdryers, etc.)