magnetism: forces created by moving electrons that act on … · 2019. 8. 12. · the permanent...

Magnetism: Forces created by moving electrons

that act on magnets.

Magnet: a material that gives off an external

magnetic field, making it possible to apply a force

on other magnets (on moving electrons) from a

distance.

Magnetic Force

• Magnetic poles cannot be isolated.

• All magnets have a

Positive end and a Negative end.

The positive end of a magnet is defined as the side that is pulled

towards the "top" of the Earth.

N

Like a pipe with flowing water.

No matter where you cut it

there is always an "in" end and an "out" end.

Magnetic DomainsAll atoms have the potential to be magnetic due to the magnetic properties of spinning electrons.

– In magnetic elements, each atom behaves like a magnet with north and south poles, all aligned to make a magnetic field.

– In nonmagnetic elements, these magnetic domains are not always aligned, thus resulting in no apparent magnetism.

001 MAGNETS veritasium

Magnetic Field lines point out of the positive end and into the negative end. And they show the direction the positive end of a magnet would be pushed.

Earth’s Magnetic FieldThe metals inside the Earth are flowing which creates moving electrons, which creates a magnetic field.

The North Pole of a magnet is attracted to the Geographic North pole of the Earth (which is actually the south pole of the giant magnet inside the earth.

Magnetic Field

Opposites attract

Magnetic fields result in a force that is either attractive or

repulsive.

Like repel

02 Magnetic Fields dave

When a certain objects are placed in a magnetic field (near a magnet), its microscopic magnets all line up, turning it into a magnet temporarily.

FerromagnetismFerromagnetism: phenomenon where objects placed in a

strong magnetic field become magnetized due to the poles

within their atoms aligning (all e- in same direction).

This is how

nonmagnetic

elements like

iron, cobalt or

nickel can

become

attracted to

magnets.

FerromagnetismFerromagnetism: phenomenon where objects placed in a

strong magnetic field become magnetized due to the poles

within their atoms aligning (all e- in same direction).

This is how

nonmagnetic

elements like

iron, cobalt or

nickel can

become

attracted to

magnets.

Electricity and Magnetism

Moving electric charge (current) can produce a magnetic field.

This means a conductor carrying current will become a magnet.

The greater the current, the stronger the magnetic field that

will be produced.

The direction of the push depends on the direction the electrons

are moving.

Electromagnets• Electromagnet: temporary magnet made by placing a piece

of iron inside a current carrying coil of wire.

Switch open

No current

Nail not magnetic

Switch closed

Current flows

Nail is magnetic

03 Electromagnetism Hymel

04 Electro magnets relativity veritasium

Electric Motor: device that uses the magnetic field created by a

current (electro magnet) to push other magnets.

• Converts electrical energy into mechanical energy.

As the current flows through wires, the wires become magnets which push against the permanent magnets. Causing movement.

Faradays Law

Changing magnetic fields causes the electrons in a wire to be

pushed (emf or voltage is created).

If the wire is NOT a loop, then the electrons will not move or flow,

but they will "feel" the push. (emf)

This push only occurs when the magnetic field exposed to the

wire is changing. If a wire is just sitting next to a magnet the

electrons are not pushed.

Faradays Law IOW

Moving magnets push on electrons

Moving electrons push on magnets.

crash course #34 (short edit)

Even though the electrons are being pushed

by the changing magnetic field, the magnet

does not get pushed back until the electrons

are start to move.

Lenz's Law

If the emf created by a changing magnetic field (Faradays Law) is

allowed to move the electrons (create a current).

Then:

The current will create its own magnetic field which will be in

opposite direction to the original magnetic field.

This opposing magnetic field will push on the magnet opposing

its motions.

Lenz's Law

IOW:

When a magnet (moving closer to a conductor) creates a current.

The current creates a magnet that will push back on the

approaching magnet.

Moving magnets push electrons (create voltage)

Moving electrons push magnets (create magnetic fields)

When magnets move past electrons (or electrons move past magnets), the electrons create a magnetic field that pushes on the magnet, and the magnet creates an electric field that pushes on the electrons.

These forces always oppose the motion that made them in the first place.

Magnets do not push on electrons that are not moving.

Video "10 magnets and copper"

Electric Generator: device that uses the eclectic fields (emf)

created by moving magnets to push electrons.

• Converts mechanical energy into electrical energy.

A generator spinning with no load, has little current in the wires,

therefore the wires do not become a magnet that would push back on the

moving magnets. It is easy to turn a generator with no load.

A generator with magnets moving past wires will only have a resistive

force (opposing magnetic field) if current is allowed to flow through the

wires.

When a load is present, current will flow through the wires and make a

magnetic field that pushes back on the rotating magnets, making it difficult

to turn. (the wire magnets push on the permanent magnets.

A generator can be used as a break.

Video "11 magnetic breaking"

Electric Motor: device that uses the magnetic fields created by

moving electrons to push magnets.

• Converts electrical energy into mechanical energy.

A spinning electric motor has +12 v applied to it pushing electrons

through the wires. This turns the wires into magnets that push the

permanent magnets and make them move.

The now moving permanent magnets go past the wires and generate a

push on the electrons of the wire as they go past them.

The permanent magnets will push the electrons opposite the direction the

+12 v from the power source was pushing. (back emf = negative volts).

This opposite voltage on the electrons of the wire created by the moving

magnets is called back emf. And it greatly reduces the net force on the

electrons so there is less current. +12v and -10v = +2v

When a load slows down the magnets there is less back emf, so there is

more net voltage on the wires and more current. +12v and -4v = +8v

The result of all this back emf-ing is:

GeneratorsIt is easy to turn the shaft of a generator that does not have a load. And the greater the load (more current) the harder it is to turn the shaft of the generator.

MotorsA motor that has no load will not use much electricity. (due to back emf). A motor that slows under load will use much more electricity (more current).

If a voltage forces electrons to move through the wires this will force the magnets (shaft) to turn.

Electric Motor

Moving Electrons push magnets

Most electric motors have a thermal overload breaker. If the motor stalls a lot of current will flow through the wires and cause them to heat up. The thermal switch cuts powers until the motor cools off.

Reset

If the magnets (shaft) is forced to move then voltage will be created in the wires forcing the electrons to move

Generator Moving magnets push electrons

Copper can stop a magnet.Could a magnet stop a copper bullet?

Video: Strongest magnets in the world.

RS #27 magnetism