The Physics of Electricity and Magnetism

Making a Magnet

9-12 Science Std: Phys 5h, 5j

First, a quick review about magnetsMagnets are usually metals or ceramic

•They come in many shapes

•Horseshoe magnets

•Flat magnets that can go on a refrigerator

•Bar magnets

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First, a quick review about magnetsBut these magnets all have some things in common…

•They all attract things that contain iron

•Nails, paper clips, etc

•They are most strongly attracted to the ends of the magnets – called the poles of the magnet•There are 2 poles – called the North Pole and the South Pole

•Opposite poles attract, same poles repel

•Lines of force (magnetic field) surround the magnet going from north to south

First, a quick review about magnetsAnd you have heard of electromagnets…..

•Wrap some wire around a nail and put current through it…

•And you get a magnet just like a bar magnet with a north and a south pole…

•But how does a bunch of electrons moving through a wire make a magnetic field?

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How does this work?Scientists in the late 1700’s started working on this…

•They thought that electricity and magnetism worked together somehow

•But no one had an idea how they worked together

•So they didn’t know where to start….

How does this work?Then in 1820, an experiment was done…..

•Hans Oersted did an experiment with a wire and a compass

•He held a wire next to a compass and ran a current

through it

How does this work?Then in 1820, an experiment was done…..

•When the current was turned on….

•The needle of the compass turned away from pointing

towards North

How does this work?Then in 1820, an experiment was done…..

•When the current was turned off

•The needle went back to pointing to North

•Disc 19 Demo 8

How does this work?Why did the compass needle move?

•When an electrical current flows through a wire

•A Magnetic field is created by the moving electrons that wraps around the wire

How does this work?Why did the compass needle move?

•Here is a video demonstration showing the magnetic field around a wire…..

•Disc 19 Demo 9

Lets look at the magnetic field….Which way does the magnetic field go?

•From the video we

saw that the iron filings

made a circle

around the wire

Lets look at the magnetic field….Which way does the magnetic field go?

•We also saw how the iron filings take

shape around a coil of wire…

Lets look at the magnetic field….But why does the magnetic field have these shapes?

•When the current goes through the

wire

•A circular magnetic field wraps around the wire using

the Right Hand Rule

Lets look at the magnetic field….What is the Right Hand Rule?

•Imagine your pencil is a wire carrying an electrical current

•Now picture the current going from the bottom of the pencil to

the top….

Lets look at the magnetic field….What is the Right Hand Rule?

•Now take your right hand

•And wrap it around the pencil with your thumb pointing in the direction

the current is going

Lets look at the magnetic field….What is the Right Hand Rule?

•Your fingers are wrapped in the direction of the magnetic field

Lets look at the magnetic field….What is the Right Hand Rule?

•We can see this better in the video

demonstration using a wire and a

compass….

•Disc 19 Demo 7

So now lets try it ourselves…..Using the Right Hand Rule…

•If we have a wire like the one here…

•And the current is flowing from top to

bottom….

•Which way is the magnetic field going

to go?

So now lets try it ourselves…..How about this one….

•If we have a coil of wire…..

•And the current is flowing from top to bottom….

•Which way is the magnetic field going to go?

•Disc 19 Demo 10

•So this will look just like a bar magnet!

Important things to remember…•Electrical current makes a magnetic field

•The more the current, the stronger the magnetic field

•The direction of the magnetic field is shown using the Right Hand Rule

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Important things to remember…

•Current through a coil of wire makes an electromagnet

•Electromagnets are just like regular magnets

•They have north and south poles

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