Magnets and Magnetic Fields

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What do you know about magnetism?

Electricity and magnetism are related!

Modeling independent work compare notes

Magnetism Readings

Turn and talk

…Partner closer to the door What is a magnetic field?

…Partner farther from the door What causes a magnetic field?

Magnetism Readings

Turn and talk

…Partner closer to the door What is a magnetic field?

A magnetic field is an area around a moving charge that exerts a force

on other moving charges / other magnetized objects.

…Partner farther from the door What causes a magnetic field?

Magnetic fields are creating by moving charges / current.

Magnetism Readings

Turn and talk

Compare and contrast electric fields and magnetic fields.

Magnetism Readings

Turn and talk

Compare and contrast electric fields and magnetic fields.

Electric fields are areas around stationary charges that can exert a force on other charges. Magnetic fields are areas around moving charges that can exert a force on other moving charges / magnetized objects.

Magnetism Readings

Types of MagnetsMagnetic fields are created by moving electric charges … where are the charges??

Types of MagnetsMagnetic fields are created by moving electric charges … where are the charges??

Electromagnets◦ Magnetic field created by electric current◦ Can be turned on/off◦ Examples: junk yard cranes, components of motors,

transformers, generators, speakers, etc.

Types of MagnetsPermanent MagnetsThe charges are the spinning electrons of the atoms!

◦ All objects have spinning electrons, and each spinning electron has a mini-magnetic field around it

◦ Usually, each mini-magnetic field points in a random direction

◦ In a permanent magnet the mini-magnetic fields are aligned

non-magnet magnet

Types of MagnetsPermanent MagnetsThe charges are the spinning electrons of the atoms!Examples:

◦ Fridge magnets◦ A compass needle◦ The Earth!

Types of MagnetsTurn & TalkPartner with longer last name…

◦ Compare and contrast permanent magnets and electromagnets

Partner with shorter last name …◦ Identify an example of a permanent magnet and an

electromagnet

Magnets are Cool! North (+) Pole and South (-)

Pole Opposite Attract Likes Repel

N

S

S

N

N

S

N

S

We can NEVER pull apart magnetic dipole. When we cut magnet in two we end up with two smaller dipoles. If we keep on cutting, more magnets will be produced, EACH with north and south pole.

Let’s Break A Magnet!NS

S SN N

S NS N S NS N

Magnetic monopoles have never been detected.

We can NEVER pull apart magnetic dipole. When we cut magnet in two we end up with two smaller dipoles. If we keep on cutting, more magnets will be produced, EACH with north and south pole.

Let’s Break A Magnet! NS

S SN N

S NS N S NS N

Magnetic monopoles have never been detected.

Just for fun …

Ever wonder why fridge magnets don’t seem to have poles … they do!

Earth’s A Magnet!The poles received their names because of the behavior of a magnet in the presence of the Earth’s magnetic field. The pole of a magnetic needle that points to the north of the Earth is called north pole. So, magnetic pole which is in the geographic north is magnetically south pole.

Earth's magnetic field has flipped many times over the last billion

years.

Don’t freak out:

NS

NS

The Magnetic Field

The direction of the magnetic field at any location is the direction in which the north pole of the compass needle points at that

location.

A magnetic field is said to exist at a point if a compassneedle placed there experiences a force.

Field Lines of Bar Magnet

Magnetic field lines don’t start or stop.

There are no magnetic charges (monopoles)

But don’t be confused if you see pictures on the right (technically wrong, but

commonly drawn)

Magnetic Field Lines

+-

– Arrows give direction to which a north pole will orient

– Density gives strength– Looks like dipole!

Which diagram shows the correct field lines of a bar magnet?

(1) (2) (3)

Question

Field lines do NOT stop abruptly

Field lines should always

point south

Place a magnet on a sheet of notebook paper and trace its outline.

Move a compass around the magnet, and sketch the field lines (where the north needle points)

Magnetic Field Lines activity

Include definition, picture, and where appropriate, variable and units and releavant equations.

electric field magnetic field charge current permanent magnet electromagnet resistance potential potential energy power work force

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