Magnetism

Magnetism• The Greeks discovered a mineral that had a peculiar property

• It attracted metals, they found it in a place called Magnesia so they called it magnetic!

• Magnetism – refers to properties and interactions of magnets• Can be made of iron, cobalt, or nickel

Magnetic Force• Not only do magnets attract metal objects, they also exert a force on each other

• Magnetic force – the attraction or repulsion felt between magnets

Magnetic Field• A magnet is surrounded by a magnetic field which exerts the magnetic force

• Objects made of iron or another magnet are within the field it will react• The field can be shown with lines of

force or magnetic field lines

Magnetic Poles• Magnetic Pole – area of a magnet where the magnetic force exerted is the strongest• North and South poles• North pole will point “North” like

a compass• Field lines always connect from

north pole to south pole

Magnetic Poles

Magnetic Poles

Earth’s Magnetic Poles• Earth’s magnetic poles are opposite of what you would think!

• The N end of a compass needle points north…which means…

•The north pole of Earth is the south pole of Earth’s magnet!

Magnetic Domain• Magnetic Domain – groups of atoms aligned with magnetic poles• In a magnet, all magnetic domains are aligned

Isolated poles?!• Can we break a magnet in two?

• Sure we can! But what happens to the poles?

• There will still be a north and south pole!

Electricity and Magnetism• Sometimes it helps to be lucky…• In 1820 a Danish physics teacher was demonstrating electric circuits• He had left a compass nearby the circuit and noticed as electricity was

flowing, the compass was deflected• He hypothesized that an electric current must produce a magnetic field

Right Hand Rule• Moving charges flowing through a wire create a magnetic field

• The field forms a circular pattern around the wire• Direction of field depends on the current• The strength of the field depends on the strength of the current

Right Hand Rule• The right hand rule helps determine the direction of the magnetic field• Current = I•Magnetic field = B

Electromagnets• Electromagnet – a temporary magnet made by placing a piece of iron inside a current-carrying coil of wire• Temporary because they only

work while current is flowing

Magnets Make Music• Speakers work because of electromagnets!• Information is read from a CD• That information varies electrical

current through a coiled wire• The electromagnet that is created is

attracted or repelled by a fixed magnet within the speaker• The causes vibration which creates

sound!

Galvanometer• Galvanometer – a device that uses an electromagnet to measure electric current• Often used for gauges in a car• The greater the current the stronger

the electromagnet• The needle will push against a spring

to align with the poles of a permanent magnet

Electric Motors• Electric motor – device that converts electrical energy into mechanical energy◦ Electric motor contains an

electromagnet that can rotate freely inside a permanent magnet

◦ When current flows the electromagnet produces a magnetic field

Electric Motors• By flipping the flow of the current the poles of the electromagnet are switched and the coil can continue to rotate

•In some motors a communicator flips the flow of the current

• The greater the electric current the faster it will spin

Question…• So we’ve seen that using an electric current and a magnet we can create a running motor

• What if we turned the current off and turned the wire coils ourselves?

Electromagnetic Induction• Electromagnetic induction – producing an electric current by moving a loop of wire through a magnetic field

Generator• Generator – produces electric current by rotating a coil of wire in a magnetic field

Switching Direction• As the coil turns inside of a fixed magnet, the current will switch direction• This results in AC electric current!

Power Plants• In order to generate power for you home and for cities power companies use massive generators

•Turbine – a large wheel pushed by water, wind, or steam

Direct vs. Alternating Current• Two forms of electric current• Direct current (DC) – flows only in one direction in a wire• Batteries• Alternating Current (AC) – flows in 2 directions and alternates direction

in a regular way• Outlets in your home• 60 Hz in N. America

Transformers• No…not Optimus Prime

• Transformer – a device that increases or decreases voltage of an alternating current

Transformers

Transformers• Step-up transformer• Secondary coil has more turns• This increases the voltage• Ex. Primary coil is 60V if the

secondary has 2 times the turns the secondary voltage will be 120V• 60V x 2 = 120V

• Step-down transformer• Secondary coil has fewer turns• This decreases the voltage• Ex. Primary coil is 120V and

secondary has half as many turns the secondary voltage will be 60V• 120V x ½ = 60V

Alternate Forms of Energy Hydroelectricity – creating electricity from moving water

Alternate Forms of Energy Solar Energy – using the sun’s energy to create electricity

Alternate Forms of Energy Wind Energy – Using wind turbines to produce energy