Basis of DC Motor Action

Magnetic Field Tippler

Field of a Permanent MagnetNorth to south outside the magnet; south to north inside the magnet

N S

Field of an Electromagnetis similar to that of a permanent magnet

N SN S

Oersted Experiment Tippler

Compass on Top of the Wireshows approximate direction of field as the result of current flowing in

the wire

Compass on Bottom of Wirefor current flowing in the same direction as before

Field Around a Current Tippler

Field Around Current-Carrying Wireschematically showing the direction of the field around the wire for

current flowing in the direction shown in the wire

Right Hand RuleFrom http://micro.magnet.fsu.edu/electromag/electricity/generators/

Electromagnet and One Loopshows that the field inside the loop is always in the same direction

N S

Three-Dimension Demonstration

Opposite Poles Attractso if the center magnet is can rotate around its midpoint, it will tend to

line up with the two fixed magnets

N S

N

S

NS

N

Momentum Causes Overshootso the direction of rotation will be reversed by the magnetic attraction

N S

N

S

NS

N

N

SN S

N S NS

And finally stops

N S

N S

N

S

NS

N

N SN S N

S

N S N S

Opposite Poles Attractso the center electromagnet rotates

NS

N S

N SN

If the direction of the current changes just as the electromagnet passes the fixed magnets, like

poles repel causing the electromagnet to continue rotating.

N SN S

N S

N SN

SS

N

S

Rotation Continues

N SN S

N S

N SN

S

N

S

S

N

S

N S N S

The direction of the current can be changed if the ends of the wires brush along the fixed + and – contacts as the electromagnet rotates.

+

_

brushes

rotates

stationary

• Go to motor applet

• http://www.walter-fendt.delph11e/electricmotor.htm