Magnets

And Magnetic Fields

Review

• Just like Electricity, magnets work in FIELDS.

• Fields are drawn with VECTORS

• Review:Up, Down, Left and Right

Review

• With Magnetism, we will need to look at vectors in 3-D.

• How do we draw a vector arrow going into the page?

• What would a real arrow look like going away from us?

Review

• Kind of like this:

• So we draw it like this:

Review

• What would a real arrow look like coming directly toward you?

Review

• Like this:

• So we draw it like this:

Magnetism

• Magnetism works in a field, like Electricity.

• We use B for the magnetic field variable.

Magnetism

• Magnets work a lot like a PROTON and an ELECTRON.

• Imagine a bar of metal with all the PROTONS on one end and the ELECTRONS on the other.

+ + + + + + + + +

- - -- - -- - -

Magnetism

• The left side is positively charged, right side negatively charged and the field would look like this:

+ + + + + + + + +

- - -- - -- - -

Magnetism

• If this were a magnet, there would be a North and South pole instead. Field looks the SAME

+ + + + + + + + +

- - -- - -- - -

N S

Electricity and Magnetism

• Electricity and Magnetism are “chained” together.

E & M

• Whenever you have an ELECTRIC CURRENT, there is a MAGNETIC FIELD too, and vice versa.

• One is always quite larger than the other.

E & M

• Ever had a power cord to close to a TV screen?

• The distortion is from the Magnet Field around the cord.

E & M

• Example: Current vs. Magnetic Field in a power cord

LARGE current SMALL magnetic field

E & M

• Other Examples:• High Voltage Power lines

Big V Small B• MRI Machine

Huge V Medium B• Refrigerator Magnet

Medium B Tiny V

Magnetic Fields

• How do we know what the Magnetic Field looks like around a wire with current in it?

Magnetic Fields

• There are some rules to help us.

• They are called Right Hand Rules.

Step 1: USE YOUR RIGHT HAND!!

Right Hand Rule #1

• What does a magnetic field, B, look like around a wire?

• Grab some wire with your RIGHT hand

I

Right Hand Rule #1

• Make sure your thumb is going in the same direction as the current is!

I

Right Hand Rule #1

• Your 4 fingers are lined up with the magnetic field. It goes in a circle around the wire.

I

Right Hand Rule #1

• A field diagram would look like this:(Remember the vector arrows)

Front Top Bottom

I

II I

Right Hand Rule #2

• What happens if we play with an electric cord in a magnetic field that was already there?

Right Hand Rule #2

• We’ll set it up like this:

I

N (+)

S (-)

Right Hand Rule #2• Even without the wire, the magnets have a

field already:

N (+)

S (-)

B

Right Hand Rule #2• So what happens when the power is turned

on? The wire starts moving! But what direction??

N (+)

S (-)

B

I

Right Hand Rule #2• Right Hand Rule #2 tells us in what direction

the wire will be pushed…

N (+)

S (-)

B

I

Right Hand Rule #2• STEP 1: USE RIGHT HAND!!!

N (+)

S (-)

B

I

Right Hand Rule #2• Index Finger points with B.

N (+)

S (-)

B

I

Right Hand Rule #2• Other three point with I

N (+)

S (-)

B

I

Right Hand Rule #2• Stick your thumb out. That’s the direction of

the force (the way the wire will go).

N (+)

S (-)

B

I

Practice

• The 2nd Right Hand rule will take some getting used to:

• #1- Index finger with B

• #2- Other three with I

• 3#- Thumb gives you the answer