Magnetic Fields Produced by CurrentsFebruary 14, 2007

Moving Charges Produce Magnetic Fields “moving charges” = “current”

Right hand rule for currents (RHR-2):

Thumb in direction of current, fingers curl in direction of B-field.

I

r

B0

2

IB

r

Long, straight wire

I2

L

r

RHR-1:

Fingers along BThumb along vPalm shows F

12 sin( )I LBF (eqn 21.3 in book)

I1

0 11 2

IB

r

Example: Two Wires (opposite directions)

I2

L

RHR-1:

Fingers along BThumb along vPalm shows F

12 sin( )I LBF (eqn 21.3 in book)

I1

0 11 2

IB

r

Example: Two Wires (same direction)

r

Loop of Wire (N=1 turn)

RHR-2

Thumb along current IFingers curl along B

0

2

IB N

R

Loop with N Turns: Current I

B

Adding Loops of Wire (same radius)

0

2

IB

R

X 1X 2X 3X 4

0

2

IB N

R

Loop with

N Turns

The Solenoid

0BL

IN

Nn

L

I I

Similar (but not exactly the same) to adding N turns of wire with equal radius:

B

But let’s just call

0B nI B-field through solenoid

L