Magnetism Notes AKA Ch 21 Super Fun Magnet Info. N S.

Magnetism Notes

AKA Ch 21 Super Fun Magnet Info

N

S

How to show magnetic fields in 3-D

Magnetic Field

Earth’s Magnetic Field

Magnetic Reversal

Magnetic Pole Wandering

http://www.ngdc.noaa.gov/geomag/GeomagneticPoles.shtml

Magnetic Field Strength

• The really interesting thing is this: ever since Gauss first measured the strength of the field, it has been dropping. Over the 170 years or so since the first measurements, the main field has decayed by some 8 or 9% and this has led to all sorts of speculation as to whether we are heading for some big geomagnetic event, like a reversal.

When a charged particle enters a When a charged particle enters a magnetic field, an electric force is magnetic field, an electric force is exerted on it. If a charged exerted on it. If a charged particle moves at an angle to a particle moves at an angle to a magnetic field, the magnetic force magnetic field, the magnetic force acting on it will cause it to move acting on it will cause it to move in a spiral around the magnetic in a spiral around the magnetic field linesfield lines..

The Aurora Borealis in the Northern HemisphereThe Aurora Borealis in the Northern Hemisphere

And the Aurora Australis in the Southern HemisphereAnd the Aurora Australis in the Southern Hemisphere

Magnetic Field Around a Wire• If electrons are flowing, they create a

magnetic field in a circular pattern around the path.

Magnetic Domain

Do magnets ever lose their magnetism? 

1) Via heat

2) Via a demagnetizing magnetic field

3) Via shock

Electric Motor

An electric motor, is a machine which converts electrical energy into mechanical (rotational or kinetic) energy.   

A current is passed through a loop which is immersed in a magnetic field. A force exists on the top leg of the loop which pulls the loop out of the paper, while a force on the bottom leg of the loop pushes the loop into the paper.

The net effect of these forces is to rotate the loop.

Motors…not too hard to build.

http://www.youtube.com/watch?v=mHD_2qYwr_Y

Electromagnet (Magnetism from Electricity)

An electromagnet is simply a coil of wires which, when a current is passed through, generate a magnetic field, as below.

A Simple Electromagnet:

Magnetic Levitation (Maglev)

Magnetic field, Current, and Force are all perpendicular to each

other….

• Draw three lines that are perpendicular to each other:

Defining Magnetic Field Direction

Magnetic Field vectors as written as B

Direction of magnetic field at any point is defined as the direction of motion of a charged particle on which the magnetic field would not exert a force.

Magnitude of the B-vector is proportional to the force acting on the moving charge, magnitude of the moving charge, the magnitude of its velocity, and the angle between v and the B-field. Unit is the Tesla or the Gauss (1 T = 10,000 G).

Right Hand Rule

Try to fit your hand to this diagram….

Try this one out:Where is the force pointing?

Try these for practice:

Formulas

F = B I l sin θ

What happens if the particle is negatively charged like an

electron?• http://homepages.ius.edu/kforinas/phys

lets/magnetism/magnetH.html

Now, take some time for the ones on your worksheet

Warm-up 4/301. Tell your neighbor what you think the

answer should be:

2.How would the answers be different for an electron?

What happens if you cut a magnet in half?

A) it becomes demagnetized

B) you get a separate south pole and a separate north pole

C) you get monopoles

D) you get two magnets