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Left Hand Rules. by Richard J. Terwilliger. Left Hand Rule. st. Left Hand Rule. 1. Left Hand Rule. B. Click on a. i. N. LEFT HAND RULE. S. rd. 3. nd. 2. F. Left Hand Rules. Created by Richard J. Terwilliger July 2001. Left Hand Rule. st. Left Hand Rule. 1. Left Hand Rule.

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slide1

Left Hand Rules

by

Richard J. Terwilliger

slide2

Left Hand Rule

st

Left Hand Rule

1

Left Hand Rule

B

Click on a

i

N

LEFT HAND RULE

S

rd

3

nd

2

F

Left Hand Rules

Created by

Richard J. Terwilliger

July 2001

slide3

Left Hand Rule

st

Left Hand Rule

1

Left Hand Rule

B

i

N

S

rd

3

nd

2

F

Left Hand Rules

slide4

st

1

Left Hand Rule

e

e

e

e

e

e

Magnetic Fields

around current bearing wires

slide5

st

1

Left Hand Rule

e

e

e

e

e

e

Thumb points in the direction of electron flow.

Fingers curl around the wire in the direction of the magnetic field.

slide6

N

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

slide7

N

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

slide8

N

The magnetic field above the wire points into the page.

slide9

N

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

slide10

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

slide15

Out of the page is shown by a dot

X

Into the page is shown by an X

slide16

X

Out of the page is shown by a dot

X

Into the page is shown by an X

X

slide17

X

Out of the page is shown by a dot

X

Into the page is shown by an X

X

slide18

e

e

e

e

e

e

LEFT

Grasp the wire with your hand

The current flow is now to the left

slide19

e

e

e

e

e

e

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.

slide20

e

e

e

e

e

e

X

X

X

X

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.

slide21

e

e

e

e

e

e

The current flow is now to the left

X

X

X

X

The thumb points in the direction of electron flow,

the fingers curl around the wire in the direction of the magnetic field.

slide22

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.

slide23

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

CORRECT

WRONG

slide24

?

CORRECT

WRONG

Is the diagram at the left correct?

X

X

X

X

X

X

The diagram is…

slide29

Loops

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

slide30

negative

Loops

The electrons flow from the negative terminal of the battery

slide31

positive

Loops

through the wire and back to the positive terminal.

slide32

Loops

through the wire and back to the positive terminal.

slide33

Loops

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

slide34

We use the

Left Hand Rule

to determine the direction of the magnetic field.

nd

2

Loops

slide35

Left Hand Rule

nd

2

for

Loops

Coils

and

The arrows show the direction of electron flow.

Fingers curl in the direction of the magnetic field

slide36

Grab the loop with your

Left Hand Rule

LEFT HAND

nd

2

for

Loops

Coils

and

slide37

Left Hand Rule

nd

2

for

Loops

Coils

and

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

slide38

Left Hand Rule

nd

2

for

Loops

Coils

and

Your thumb now points

S

NORTH

N

slide39

S

N

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

slide40

S

N

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

slide41

N

S

N

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

slide42

N

N

N

S

N

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

slide45

We also use the

Left Hand Rule

to determine the magnetic field around a coil.

nd

2

Coils

slide46

To demonstrate the

Left Hand Rule

we’ll start by building an electromagnet.

nd

2

Coils

slide54

Next attach a potential source

(battery)

to the wire.

slide60

The

Left Hand Rule

is used to determine the direction of the magnetic field.

nd

2

slide62

Left Hand Rule

nd

Your thumb points to the end of the coil

2

NORTH

Grasp the coil with your left hand curling your fingers around the coil in the direction of electron flow.

N

for loops and coils

slide63

Left Hand Rule

nd

2

S

N

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

for loops and coils

slide64

?

S

N

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

slide65

S

N

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

slide66

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

slide70

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

slide73

Use the

Left Hand Rule

to determine the NORTH end of the coil.

nd

2

slide77

You thumb points to the

NORTH

end of the coil.

N

slide78

We now know the

SOUTH

end of the coil.

S

N

slide79

and the

MAGNETIC FIELD LINES

around the coil.

S

N

slide82

?

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

slide83

We do know that

NORTH

is on the bottom of the coil

?

NORTH

slide84

Using the

Left Hand Rule

determine which is the negative terminal.

A

or

B

?

nd

2

A

B

NORTH

slide85

Grab the coil with your

Left Hand

so you thumb points

NORTH

?

A

B

NORTH

slide88

The

Electrons

must come from

B

?

A

B

NORTH

slide89

The

Electrons

must come from

B

?

A

B

NORTH

slide90

Therefore is the

NEGATIVE TERMINAL

B

?

A

B

NORTH

slide92

Left Hand Rule

rd

3

Now the

slide93

There are 3 partsto the

3 parts

3

Left Hand Rule

rd

3

slide94

one

An external magnetic field.

rd

3

Left Hand Rule

slide95

NORTH

SOUTH

to

rd

3

Remember that the magnetic field goes from

Left Hand Rule

slide96

two

Either a charge moving across the magnetic field.

rd

3

Left Hand Rule

slide97

rd

3

two

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

Left Hand Rule

slide98

three

Force

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

rd

3

Left Hand Rule

slide99

rd

3

I will now show you how to apply the

Left Hand Rule

slide100

SOUTH

SOUTH

Point your fingers

slide101

Or the same direction as the

MAGNETIC FIELD

SOUTH

slide103

And the

FORCE

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

-i

SOUTH

FORCE

slide104

rd

3

Let\'s try it with our example

Left Hand Rule

slide105

rd

3

First point your fingers of your left hand

SOUTH

Left Hand Rule

slide106

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

rd

3

B

B

Left Hand Rule

slide108

Force

rd

3

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

-i

B

Left Hand Rule

slide109

Force

rd

3

So the force acting on the wire is

UP

-i

B

Left Hand Rule

slide110

rd

3

Let’s try another example

Left Hand Rule

slide111

N

S

rd

3

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

Left Hand Rule

slide112

N

rd

3

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

S

Left Hand Rule

slide113

Left Hand Rule

N

rd

rd

3

3

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

S

Left Hand Rule

slide114

N

rd

3

Using your left hand point your fingers

SOUTH

S

Left Hand Rule

slide115

N

rd

3

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

S

Left Hand Rule

slide116

N

rd

3

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

S

Left Hand Rule

slide118

N

Current Flow

Magnetic Field

Negative electron flow

Points at south

S

Force

Out of palm

slide119

N

S

N

S

A current bearing wire is place between two bar magnets.

What is the direction of the force on the wire?

slide120

N

S

N

S

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

slide121

N

S

N

S

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

slide122

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

N

S

N

S

slide123

We can now use the

rd

Left Hand Rule

3

to find the direction of the force on the wire.

N

S

N

S

slide124

Point the fingers of your

Left Hand

in the direction of the magnetic field, south.

N

S

Fingers point south

N

S

slide125

current flow

N

S

Fingers point south

N

S

Your thumb points in direction if the negative current flow.

slide126

current flow

Force on wire

N

S

Fingers point south

N

S

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

slide127

Force on wire

N

S

N

S

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

slide128

Force on wire

N

S

N

S

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

slide129

Have fun using the

Left Hand Rule

rd

3

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