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# Any expert at Magnetism out there?

## Any expert at Magnetism out there? - Physics Forum

### Any expert at Magnetism out there? - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

#1
01-09-2006, 04:22 AM
 rAgAv Guest Posts: n/a
Any expert at Magnetism out there?

I want to know how a magnet which is in the shape of a hollow
cylinder,behaves.(i.e which will be the north-pole and which will be
the
south pole.)
The height of the cylinder is about 15cm, and the radius r1 is 2.5cm
and r2 is 10cm.

In order to make an electro-magnet of the same dimentions, where should
the wire-wrapping start?Where should the terminals of the wire connect
(i.e AC current or DC current?)

What should be the nature of the material of the electro-magnet?
And also the wire.(Give examples)

The power with which the magnet attracts or repels depends on the
electricity input, but how do we measure the magnitude of attraction or
repulsion?Do we have any specific scale for that?

Do we have any material which would prevent the magnet from influencing
the surrounding with its magnetic fields?

Right now i have only these questions, Please answer them, as they
might be useful for my project. The project involves practical things,
practice does'nt help)

Thank you,
rAgAv

#2
01-09-2006, 12:19 PM
 N:dlzc D:aol T:com \(dlzc\) Guest Posts: n/a
Any expert at Magnetism out there?

Dear rAgAv:

"rAgAv" <[Only registered users see links. ]> wrote in message

It behaves about the same as a solid cylinder, but the net field
is proportional to the cross-sectional area involved.

Keep the wraps about three wire diameters back from the ends.
adds less and less contribution to the internal field. Use DC
current. AC will tend to heat your cylinder material, and will
turn this electromagnet into a "degaussing coil".

Core material should be iron, steel for maximum effect. Google
"ferromagnetism".

Lowest resistance to keep from heating the core unduly. Copper.

A couple are in use. The Tesla is (I think) current. You can
measure the deflection of a charged particle beam (electrons).

The container would need to be ferromagnetic, and a few
continuous layers might be necessary. It serves to "redirect the
magnetic flux lines from pole N to pole S" without involving the
entire Universe to do it.

David A. Smith

#3
01-11-2006, 07:12 PM
 Chris Guest Posts: n/a
Any expert at Magnetism out there?

I suggest you buy a school book of physics for 14 -15 year olds and do the
exercises. You could also go to evening classes on the same subject.

This is not a criticism but if you miss out on education, going back to the
begining is necessary if you are to get any where. However, I'm warning you
that the magnetism theory I learned at school is out of date and will soon
be replaced by an entirely different view.

I suggest you get to reading the practical details of construction first and
that is where to start.

Normally you just need a soft iron rod (soft is a meterlurgical term so ask
for that in the metal shop) with thick (16 guage) enamelled copper wire
wound round in a regular helix. Go from one end to the other looping the
wire round the rod in the same direction and then keeping the direction of
the loops the same wind the second layer over the first.

You do not need many turns, depending on the application the strength of the
magnet depend on currentXnumber of turns so if you use 100 turns (about
right for hand wound magnets) and have a current of 5 Amps (use a regulated
power supply) you will have a field strength of 500 Ampere-Turns.

To get the polarity write the letter S put arrows on the ends of the curve
and the current going that way looking at the end gives you the south pole.

Chris.

 Tags expert , magnetism

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