by Richard J. Terwilliger

Click on a Created by Richard J. Terwilliger July 2001

around current bearing wires

Thumb points in the direction of electron flow. Fingers curl around the wire in the direction of the magnetic field.

The magnetic field in front of the wire points towards the top of the page.

The magnetic field behind the wire points towards the bottom of the page.

The magnetic field above the wire points into the page.

The magnetic field below the wire points out of the page.

Again, The thumb of the left hand points in the direction of electron flow The fingers curl around the wire in the direction of the magnetic field

The magnetic field in front of the wire is to the left

The magnetic field on the left side of the wire is back into the page

The magnetic field behind the wire is to the right

The magnetic field on the right side of the wire is pointed out of the page

Into the page is shown by an X Out of the page is shown by a dot

Into the page is shown by an X Out of the page is shown by a dot

Into the page is shown by an X Out of the page is shown by a dot

The current flow is now to the left Grasp the wire with your hand

The current flow is now to the left The thumb points in the direction of electron flow, the fingers curl around the wire in the direction of the magnetic field.

The current flow is now to the left The thumb points in the direction of electron flow, the fingers curl around the wire in the direction of the magnetic field.

The current flow is now to the left The thumb points in the direction of electron flow, the fingers curl around the wire in the direction of the magnetic field.

Each of the following diagrams shows a section of wire that has been enlarged. Associated with each wire is the direction of current flow and the magnetic field around the wire. Determine which of the following diagrams are correct.

Does the diagram at the right show the correct orientation of the magnetic field around the current bearing wire?.

Arrows show the direction of negative current flow. Using your left hand, grab the wire with your thumb pointed in the direction of electron flow. Your fingers curl around the wire in the direction of the magnetic field.

Is the diagram at the left correct? The diagram is…

Is the diagram at the left correct? The diagram is…

Electrons flow out of the negative side of the potential source. Negative

Through the circuit and back to the positive side of the potential source. Positive

Therefore the current flow in the green section of wire is down as shown.

Using your hand grasp the wire with your thumb pointing in the direction of current flow.

Your fingers curled around the wire show the direction of the magnetic field.

Notice the magnetic field is going on the right side of the wire

and on the left side of the wire.

Let’s go back and try the problem again.

The diagram shows a compass placed above a current bearing wire.

The compass needle points into the page

What is the direction of the current flow in the wire? Click on your choice above.

The magnetic field above the wire goes into the page as shown by the compass.

Using your hand grasp the wire so your fingers curl over the top of the wire.

Your thumb points in the direction of negative current flow.

The current flow is to the

Negative current flow is to the right.

Let’s review why.

As shown by the compass, the magnetic field above the wire goes into the page.

Grasp the wire with your hand curling your fingers over the top of the wire.

Your thumb shows the current is flowing to the right.

Shown here is a loop of wire connected to a potential source.

The electrons flow from the negative terminal of the battery

through the wire and back to the positive terminal.

We know that when current flows through a wire a magnetic field is formed.

to determine the direction of the magnetic field. We use the

Fingers curl in the direction of the magnetic field The arrows show the direction of electron flow.

Grab the loop with your

Curl your fingers around the loop in the same direction as the electron flow.

Your thumb now points

The magnetic field on the outside of the loop is from the north pole to the south pole

The magnetic field inside the loop travels from the south back to the north

If we place a compass inside the loop it points in the direction of the flux lines

Outside the loop a compass still points in the direction of the magnetic flux lines

I’m back!

Several LOOPS of wire are called a

We also use the to determine the magnetic field around a coil.

To demonstrate the we’ll start by building an electromagnet.

To build an electromagnet or solenoid we start with a cylinder.

We could use one of the cardboard rolls found at the center of toilet paper rolls

If the inside of the cylinder is hollow it is said to have an air core.

The front side of the coil is called the face of the coil.

We will start creating an electrical solenoid by wrapping wire around the core.

Each wrap is a loop of wire.

and all the loops form a coil

Next attach a potential source (battery) to the wire.

The current will flow from the negative terminal

through the wire and back to the positive terminal.

The current flowed up the back of the coil

and down the front side or face of the coil.

Current flowing through the coil creates a magnetic field.

is used to determine the direction of the magnetic field. The

The next few slides will show how to apply the to this coil.

Grasp the coil with your left hand curling your fingers around the coil in the direction of electron flow. Your thumb points to the end of the coil

The magnetic flux lines come out of the NORTH, go around and into the SOUTH.

In what direction would a compass point if placed above the coil?

A compass will point in the same direction as the magnetic flux lines at that point.

Now we are going to replace this coil with another coil that has the wire wrapped around in the opposite direction.

The battery will still be connected with the negative terminal on the left.

Watch closely so you can see the difference.

The current still travels from the negative terminal through the coil and back to to positive terminal.

Notice that the electrons travel up the face of the coil, over the top and down the back

Use the to determine the NORTH end of the coil.

Grab the coil with your

Your fingers will follow the electron flow.

Curl your fingers over the top and down the back.

You thumb points to the end of the coil.

We now know the end of the coil.

and the around the coil.

Let’s try another example.

We’ll start with another coil.

The coil is attached to a potential source but the polarity is unknown.

We do know that is on the bottom of the coil

A B Using the determine which is the negative terminal. A B

A B Grab the coil with your so you thumb points

A B Your fingers now curl in the direction of

A B

A B B The must come from

A B B The must come from

A B Therefore is the B

Now the

There are 3 parts to the

An external magnetic field.

Remember that the magnetic field goes from to

Either a charge moving across the magnetic field.

Or current flow through a conductor that is in the magnetic field.

A force acting on the moving charge or current bearing wire.

I will now show you how to apply the

Point your fingers

Or the same direction as the

Your thumb points in the direction of negative

And the acting on the current bearing wire or moving negative charge is out of the palm.

First point your fingers of your left hand

Notice that your fingers point in the same direction as the magnetic field shown by the symbol

Your thumb points in the direction of negative current flow

And the force acting on the moving charge or current bearing wire is out of the palm.

So the force acting on the wire is

Let’s try another example

Shown here is a current bearing wire placed between the north and south poles of a horseshoe magnet.

The electron flow in the enlarged section of wire is back into the page as shown by the arrows.

We can find the direction of the force on the wire using the

Using your left hand point your fingers

Now, keeping your fingers pointed south, rotate your hand so you thumb points in the same direction as the current flow.

The force on this section of wire is out of your palm or

Out of palm Points at south Negative electron flow

A current bearing wire is place between two bar magnets. What is the direction of the force on the wire?

We know that the magnetic field between the bar magnets is from the north pole to the south pole?

We also know that the current (electron flow) is out of the negative terminal, through the circuit and back to the positive terminal.

Therefore the current flow in the section of wire between the bar magnets is toward the top of the page.

We can now use the to find the direction of the force on the wire.

Point the fingers of your in the direction of the magnetic field, south. Fingers point south

Your thumb points in direction if the negative current flow. Fingers point south

The force on the wire is shown by a vector coming out of your palm. Fingers point south

The force on the wire is shown by a vector coming out of your palm.

Have fun using the