The Physics of Electricity and Magnetism Magnetic Induction of Current 9-12 Science Std: Phys 5h.

The Physics of Electricity and Magnetism

Magnetic Induction of Current

9-12 Science Std: Phys 5h

It was a very special discovery….When Oersted found that current in a wire made a magnetic field…..

Physics was changed from then on….

It was a very special discovery….But then scientists asked…..

If electricity can make a magnet…

Can a magnet make electricity?

Then in 1831…….Two scientists found a way to do it!

In England

Michael Faraday

And here in the U.S

Joseph Henry

They both found a way to do it at the same time in different places

Before 1831….The only way to make an electric current was..

Dissolving special metals in acids

Which was very expensive and dangerous

But now…..We can make electricity any time, anywhere!

To make Electricity we need:

A magnet

NS

And a piece of

wire.

Wait a second……Didn’t we say before….

To make a magnet we need:

Electricity (a current)

NS And a

piece of wire.

Yes, we did!

Wait a second……In fact, we said….

As long as charged particles are moving…

Like with an electrical current

And the current is going

through a wire

NS

A magnetic field is made using the Right Hand Rule

Wait a second……But now we are saying…..

To make an electrical current……

And you get an electrical

current!

And you use a piece of wire…

NS

You take a magnet

So how does this work…..When we made the magnetic field….

The charged particles were moving…

And they were moving because of an electric field or voltage potential…

Which is an electrical current

So how does this work…..So now to make the electrical current…..

We still need some movement…..

But this time instead of moving the current to make the magnet….

NS

So how does this work…..So now to make the electrical current…..

We still need some movement…..

We move the magnet to make the current!

NS

So how does this work…..When we move the magnet across the wire….

The lines of the magnetic field move past the wire….

As the magnetic field lines pass the wire

It makes a voltage potential in the wire

And the voltage makes an electrical current in the wire

Let’s see this in action….Demonstration time!

On the front desk is a meter called an galvanometer

This is a meter that can measure the amount of current or voltage

And it can show the direction the current is flowing

Let’s see this in action….Demonstration time!

The more the needle moves on the meter…

The more current is flowing in the wire

The direction the needle moves…

Shows which direction the current is moving

Let’s see this in action….Demonstration time!

The ammeter is hooked up to a coil of wire

We use a coil because the more wire – the more current is made

Let’s see this in action….Demonstration time!

Then we take a magnet and move it through the coil of wire…

While the magnet is moving, watch what happens to the ammeter…… N S

Can the amount of current change?Yes it can……

The amount of current depends on…

The amount of wire

A little wire……

Makes a little current

A lot of wire…..

Makes a lot of current

Can the amount of current change?Yes it can……

The amount of current depends on…

The amount of magnetic field

A small magnet

Makes a small current

A big magnet

Makes a big current

N SN S

Can the amount of current change?Yes it can……

The amount of current depends on…

How fast the magnet moves

Magnet moves slowly

You get a small current

Move the magnet fast

And you get a large current

N S N S

Can the amount of current change?Yes it can……

So remember…….

The amount of current depends on:

1. The amount of wire

2. The size of the magnet N S

3. And how fast the magnet moves

So where can we use this?Where are some places we can use this?

To make electricity that

we use at home

But we can also use it to power a

flashlight without batteries

Important Points…..Changing magnetic fields make electric fields

Electric fields are voltages

Electric fields or voltages can be seen by using a voltmeter

Electric fields or voltages can make electrical currents in conductors

Electrical currents in conductors can be seen by using an ammeter or a voltmeter

Homework for tomorrow’s activity:You will need a cell phone

Turn off the cell phone and take out the battery

On the battery you will find 2 numbers:

xxx mAh – This the number of milliamps that your cell phone battery will make for 1 hour (mine is 950 mAh)

xx V – This is the voltage that your cell phone battery makes (mine is 3.7 V)

Bring these numbers to class tomorrow

So if you would like to take a closer look…..

N

S

You can come up and give it a try