Electromagnetic Force

Force on a Charged Particle

F= Bqv

F=force (N) B= Magnetic field

q= charge (C) N/Amp∙m or

velocity (m/s) Tesla

EXAMPLE

An electron travels at a speed of 3x106m/s through a magnetic field of 4x10-2 Tesla. How much force is acting on the electron?

F=Bqv

F= (4x10-2T)(1.6x10-19C)(3x106m/s)

F= 1.9x10-14N

Force on a Wire With Current

F=BIL

F- force(N) B- Magnetic Field

I-current(amps) (N/A∙m) or Tesla

L-length(m)

ExampleA wire 1.0m long carries 0.50amps of

current. If the force acting on the wire is 0.2N, what is the magnetic field strength the wire experiences?

F=BIL

0.20N = B(0.5Amp)(1.0m)

B = 0.40 N/A∙m

N S

F =0.20N

B = 0.4N/A∙m

I

Alternating current- Current that reverses direction due to a force and a magnetic field acting on a wire.

*Use right hand rule

N S

B

AC

D

F

Point (A)- Current is outward

Points (B) and (D)- no current, force is parallel to field

Point (C)-Current is into the wire

F

F

F

Graphing Alternating Current

IMax

-I max

0 t

*Commercial frequency is 60Hz so current changes direction 120 times per second!

A

B

C

D

A

B

C

D

Diode- Converts AC to DC by limiting the direction of the current flow

tI

Graphing Direct Current

t

I max

Doesn’t change direction

Generator-Rotating loop in a magnetic field that produce a current. Current changes direction every ½ cycle (AC).

F

F

The current changes direction due to the loop in the wire.

An outside force causes the wire loop to rotate inside a magnetic field.

Motor-Uses a current in a magnetic field to generate a force. This force allows work to be done by the motor.