Magnetism

Physical Science

Mr. Holmes

• Loadstones are:

• natural magnets found in ground

• contain iron ore (magnetite)

• earliest use as simple compass because it will align north-south

• Man-made magnets: most are made from iron, steel, nickel, cobalt

•  Magnetic substances are materials that are attracted to a magnet

Theory of magnetism most elements electrons spin opposed to one another and magnetic forces cancel each other out but in magnetic substances this spinning motion reinforces each other (domain theory)

• Law of magnetic poles– a magnet has the greatest strength at the

poles (little or no strength in middle)– ends are called poles (free ends)– hang bar magnet from ring stand – the bar

end pointing north = north pole

• Law of magnetic pole – like poles repel, unlike poles attract

Force of attraction or repulsion depends on strength of magnets and distance between poles

• Magnetic field – region around a magnet in which magnetic effects are observed, which is produced by the motion of the electric charge.

•  Lines of force – closed arc from north to south pole, never cross, most concentrated at poles

Making a magnetstroke bar of magnetic material in one

direction with a magnet (re-aligns domains)

use electricitybring magnet nearby (if soft iron)

How to demagnetize a magnetheatcontact (pass magnet alternating direction)hammering

Electromagnets

• When electric current passes through a wire – a magnetic field is produced in the space surrounding the wire

• (electromagnet = placing soft iron bar in center of coil of wire with electricity passing through it)

3 things needed to make electromagnet:soft iron bar (core)coil of insulated wiresource of electric current

• How to change strength of electromagnetvarying the number of turns of wire around

core increasing the currentvarying the thickness of corechange core material (if use wood = no

electromagnet, use cobalt = strength increased 170 times, but if you use iron = strength increased 1000 times)

۩ Electromagnet summarymagnetic field around straight wire that carries

currentbending wire into loops causes each loop to act as

a separate magnetadding more coils increased strength of

electromagnetincreasing number of electrons through wire

increases strength of electromagnetlarger and thicker iron core provides more magnetic

domains = increases strength of electromagnet

Useful Vocabulary

• Static electricity

• Volts

• Amps

• Ohmns

• V=I x R

• Electricity

• Circuits

• Parallel

• Series

• Alternating Current

• Direct Current

• Insulators

• Conductors