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Answers to Readers' Questions on Physical Science:

Electromagnetism

The following 122 comments and questions have been sent in. They are listed according to date.

List of first 10 items

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How does the diameter of the core affect magnetic strength?

Question

October 30, 2009

How does the diameter of the iron bar(core) affect the strength? How does the length of the iron bar affect the strength? What is the difference between wrapping wire, spread over 6 inches on a bar versus wrapping the same length of wire 3 layers deep spread over 2 inches?

The explanation of electromagnetism by Ron Kurtus is the best I have read. I have read many.

Frank - USA

18600

Answer

The diameter of the wire windings around the core affects the strength of the electromagnet the most. If the core isn't large enough for the number of windings and the amount of current flowing through those windings, the field can saturate the core and result in a reduction of magnetic strength.

An electromagnet gets its magnetic force from the electrons passing through the wire. Thus, the more windings there are the greater the magnetic power.

Since is is simple to set up, it would be worthwhile to experiment with some of these configurations.

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How does current make a magnet?

Question

July 11, 2009

how does current make a magnet?

aruna - India

18013

Answer

When DC electricity goes through a wire, it creates a magnetic field. Wrapping the wire around a piece of iron will align the atoms in the iron, creating an electromagnet.

A permanent magnet is different. It is a material that does not need current to cause the magnetism.

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Science project using electromagnetism

Question

January 5, 2009

Hi my name is britt. for my science project im trying to use electromagnetism. I was just wandering if you could give me some pointers on it. Also could you maybe give me a couple ideas about it. it would be appreciated grately. love britt
p.s. i have to have sources from different places. so plz write back.

Britt - USA

17058

Answer

A very simple experiment is to make a small electromagnet by wrapping an insulated wire around a large nail or iron rod. You power it with a battery and turn the electricity on by a switch or even touching wires together. You can demonstrate how you can control the magnetism in lifting up iron paperclips or small nails and then dropping them someplace else.

You can also stick a permanent magnet to the electromagnetic nail when the power is off. If you connect the battery the correct way, you can then make the magnet jump away from the electromagnet.

Loudspeakers use electromagnetism to vibrate the cone and make sound. If you can get a small loudspeaker from an old radio or even buy an inexpensive one from Radio Shack, you can do experiments causing the cone to move or vibrate.

I hope these ideas help you in your project.

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Making electromagnets repel

Question

August 16, 2008

I HAVE A PATENT PENDING. I ALSO HAVE A PUBLICATION.
QUESTION: I WANT TO KNOW,IF POSSIBLE,HOW TO GET TWO ELECTROMAGNETS,PULSATING "DC" TO REPEL ONE ANOTHER,AS LIKE POLES OF PERMANENT MAGNETS DO.

I HAVE READ:A)BY SWAPPING THE POLARITY OF "DC" SOURCE VOLTAGE,TWO LIKE POLES WILL REPEL. B)BY WRAPPING THE WIRE AROUND THE IRON CORE WITH COILS IN THE OPPOSITE DIRECTION,LIKE POLES WILL REPEL .

I WOULD LIKE TO KNOW ABSOLUTELY;HOW TO? PLEASE RESPOND WITH EXACTNESS AND CERTAINTY.

JAMES - USA

16364

Answer

Depending on the direction of the Direct Current (DC), two electromagnets can be made to repel just as permanent magnets with the same pole facing each other.

You can determine the pole of an electromagnet by the direction of the windings or the direction of the current. Use the "right hand rule" by wrapping your right hand around the electromagnet. Your fingers are in the direction of the current from (+) to (-) and your thumb points in the direction of the north seeking pole.

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What is the best material for an electromagnet core?

Question

June 19, 2008

I find some websites say iron cores are great for electromagnets and others say lead cores are great for electromagnets. I was wondering what is the BEST material for an electromagnet core.

- USA

16121

Answer

I have never heard of lead being used as an electromagnet core. You want a material that can become magnetized.

For a DC electromagnet, Magnetite or Ferrous-Ferric Oxide (Fe3O4)is considered very good. For an AC electromagnet, a soft iron or no core at all would work, depending on the use of the electromagnet.

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Retaining magnetism

Question

February 26, 2008

i need to know the name of the material which can act as such type of an electromagnet which can be magnetised by current supply and when the current is drawn off it will retain magnetism for just a couple of minutes

anuroop - India

15437

Answer

Soft iron loses its magnetism in an electromagnet when the current is turned off, but steel and nickel-steel will hold the magnetism. Note that the current must be DC for the atoms to be aligned and the steel to retain its magnetism.

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What are disadvantages of electromagnets?

Question

February 17, 2008

my message is what is dis-advantages about electromagnets?
please answer my question because this is for my report in physci100

queene chil - Philippines

15368

Answer

A disadvantage of electromagnets is that they require electricity to become magnetized. If there is no electricity available, they are not useful to pick up items.

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Why is household AC not good for electromagnet?

Question

December 29, 2007

Why is using household AC current not good in an electromagnet?

- USA

15034

Answer

The reasons it isn't a good idea for students to use household AC current in an electromagnet are that you can get a serious shock if you are not careful, and that the wires can quickly overheat and either short out or even cause a fire.

If done properly, household AC can be used for an electromagnet. For example, the electromagnets used in junk yards to pick up cars uses high voltages and currents, similar to household voltage.

I will add this material so that students do not try using AC.

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How to magnetic trains stay at the same level?

Question

December 8, 2007

Some trains ran on a track which suspends the train using a magnetic force.How does the track stop the train sinking below the platform when people get on the train and make it heavier?

Mei - United Kingdom

14936

Answer

Magnetic levitating (maglev) trains have electromagnets on the underneath of the train that repel those on the track. As the train gets heavier, indicators cause more current to be applied to the electromagnets to lift the train and keep it at a constant level.

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People who have studied the electromagnet

Question

November 5, 2007

please name some people who have studied the electromagnet, and what they have found

- USA

14712

Answer

British electrician, William Sturgeon invented the electromagnet in 1825.

A few years later Joseph Henry made a more powerful version of the electromagnet.

Samuel Morse used the electromagnet in his invention of the telegraph machine.

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