by Ron Kurtus

A total of 673 comments and questions have been sent in. They are listed according to date.

## List of next 10 letters

### Country

Basics of Magnetism Calculate emf for moving wire South Africa

Electromagnetism Hindi student has trouble understanding lessons India

Basics of Magnetism Don't have money for book on magnetism Rwanda

Magnets Increasing strength of magnets USA

Magnetism Lorentz How can I make an electromagnet? Uganda

Magnets How long will magnet strength last? Uganda

Basics of Magnetism Why are magnetic filed lines called imaginary? Tanzania

Magnetic Detection When was magnetism discovered? Ghana

Basics of Magnetism Spinning magnet to create electricity USA

Electromagnetism Types of connections used in electromagnets South Africa

Next 10

First 10 letters

## Calculate emf for moving wire

Topic: Basics of Magnetism

### Question

August 14, 2013

A straight wire with a length of 0,20m moves at a constant speed of 3,3m/s at right angles to a magnetic field of flux density 0,15T. Calculate the emf induced across the ends of the wire.another dimension is 3 m

Mahulo - South Africa

23931

The equation is emf = vLB, where v is the velocity, L is the length, and B is the magnetic flux.

## Hindi student has trouble understanding lessons

Topic: Electromagnetism

### Question

August 14, 2013

I am student of Hindi medium so i can not understant deeply all content

- India

23928

It is often difficult for students from Hindi medium schools to completely understand lessons in English. Many universities in India are now trying to help students to transition from Hindi to the global language.

Hopefully, you can find help in explaining the words in the lessons. I am sure other students in your class have the same problem.

Best wishes for success in your studies.

## Don't have money for book on magnetism

Topic: Basics of Magnetism

### Question

August 13, 2013

Hello.i'm in kigali i need that book on magnetism but i don't have money.i'm poored i can't get money.cos its my favorite course.i beg you pls.thanks

Karuzi - Rwanda

23927

We don't have a book on magnetism available, However, you can go through our free lessons to learn as much as you can.

Best wishes for success in your studies.

## Increasing strength of magnets

Topic: Magnets

### Question

August 11, 2013

do common magnets like you buy at a store, piled up on each other increase in strength by adding more magnets?
please define what a "rare earth" magnet is made from, and can stacking them increase the power?

Lee - USA

23925

Stacking magnets together can increase the strength, although not as much as you would think.

Rare-earth magnets are made of materials that are not commonly found. Neodymium magnets are the strongest and most affordable type of rare-earth magnet. Some small ones are even available in toy stores.

## How can I make an electromagnet?

Topic: Magnetism Lorentz

### Question

July 18, 2013

how can i make an electric magnet

edward - Uganda

23876

You can make an electromagnet by wrapping an insulated wire around a piece of iron, like a large nail. Then you use a DC battery to power the electromagnet. Do not use high voltage AC, because it will cause a short circuit in the wire.

See Electromagnets for an explanation and picture.

## How long will magnet strength last?

Topic: Magnets

### Question

July 18, 2013

how long can the strenth of two magnets put to repel {north to north} on a moving motion last

edward - Uganda

23875

Surprisingly, if you put two magnets of the same pole near each other (like north to north) the strength will last a very long time. The Opposing forces does not seem to degrade the magnets.

## Why are magnetic filed lines called imaginary?

Topic: Basics of Magnetism

### Question

June 22, 2013

why magnetic field are imaginary line and not true line?

mustapha - Tanzania

23800

When you see a drawing of magnetic lines, they are only representations of the flow of the magnetic field. Some call them imaginary, because you really can't see the magnetic field.

## When was magnetism discovered?

Topic: Magnetic Detection

### Question

June 5, 2013

When and where was the idea of magnetism mooted? How was the idea of magnets demonstrated at the initial stages of the "discovery" of magnets?

ATIBODU, Mohammed - Ghana

23748

Apparently an ancient Greek shepherd found a rock called lodestone that attracted iron, about 4000 years ago. Ancient Chinese also discovered properties of lodestone.

For a good rundown on the background, see: History Of Magnets.

## Spinning magnet to create electricity

Topic: Basics of Magnetism

### Question

May 29, 2013

I have a question about magnetism. If you had a 1"width x 1"Height x 4"length magnet and drilled a hole 2"down the length so it's evenly balanced and put an aluminum rod through the hole and then spin this magnet vertically or on the Y axis while moving it through (referring to the Z axis) a coil of magnet wire what type of energy would it generate assuming you are only traveling through the magnet wire coil in one direction. Would this still be ac? Would it still be a sine wave?

c - USA

23732

It is difficult to visualize your configuration. I assume using an aluminum rod is because it is not magnetic.

A sine wave current can be considered an AC signal with a DC component. One reason for grounding an AC circuit is to remove the DC component.

## Types of connections used in electromagnets

Topic: Electromagnetism

### Question

May 29, 2013

what types of connections are used in electromagnets

jaison - South Africa

23731

An electromagnet consists of an iron core that is wrapped with thin insulated electrical wire. That wire can be connected to either an AC or DC electrical source, depending on the use of the electromagnet.

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