Introduction to the Introduction to the Electric MotorElectric Motor

Electric Motors are based on Magnets, Electromagnets and

The Law of Magnetic Poles.

Electro MagnetElectro Magnet

Permanent MagnetPermanent Magnet

Every Magnet has Every Magnet has Two polesTwo poles

Even an electro-magnetEven an electro-magnet

Magnets obey the Law Magnets obey the Law of Magnetic Polesof Magnetic Poles

Like Poles Repel andLike Poles Repel andUnlike Poles AttractUnlike Poles Attract

Magnetic Force On A Current – Magnetic Force On A Current – Carrying Conductor Carrying Conductor

The magnetic force (F) a conductor The magnetic force (F) a conductor experiences is equal to the product of its experiences is equal to the product of its length (L) within the field, the current I in length (L) within the field, the current I in the conductor and the external magnetic the conductor and the external magnetic field B. field B.

Magnetic Force is Proportional to: Magnetic Force is Proportional to:

Length of the conductorLength of the conductor

Current Current

Magnetic FieldMagnetic Field

Magnetic Field Around a Current Carrying Conductor

The force on a currentThe force on a current--carrying carrying conductor in a magnetic fieldconductor in a magnetic field: :

When a currentWhen a current--carrying conductor is placed in a carrying conductor is placed in a magnetic field, there is an interaction between the magnetic field, there is an interaction between the magnetic field produced by the current and the magnetic field produced by the current and the permanent field, which leads to a permanent field, which leads to a forceforce being being experienced by the conductor:experienced by the conductor:

Fleming’s left-hand ruleFleming’s left-hand rule

The directional relationship The directional relationship of I in the conductor, the of I in the conductor, the external magnetic field and external magnetic field and the force the conductor the force the conductor experiencesexperiences

I

F

B

Motion of a current-carrying loop in a Motion of a current-carrying loop in a magnetic fieldmagnetic field

N SL R

I

F

F Rotation

Commutator (rotates with coil)

brushes

Vertical position of the loopVertical position of the loop::

N S

Rotation

Electric MotorElectric Motor

An electromagnet is the basis of an An electromagnet is the basis of an electric motor electric motor An electric motor is all about magnets and An electric motor is all about magnets and magnetismmagnetism: : A motor uses A motor uses magnetsmagnets to to create motion. create motion. Opposites attract and likes repelOpposites attract and likes repel. . Inside an Inside an electric motor, these attracting and electric motor, these attracting and repelling forces create repelling forces create rotational motionrotational motion. . A motor is consist of two magnets.A motor is consist of two magnets.

Parts of the MotorParts of the Motor

Armature or Rotor (electro-magnet) Armature or Rotor (electro-magnet)

Commutator Commutator

Brushes Brushes

Axle Axle

Permanent Magnet Permanent Magnet

DC power supply of some sortDC power supply of some sort

Motor IllustrationMotor Illustration

ArmatureArmatureThe armature is an The armature is an electromagnet made by electromagnet made by coiling thin wire around coiling thin wire around two or more poles of a two or more poles of a metal core.metal core. The armature has an The armature has an axleaxle, , and the commutator is and the commutator is attached to the axle. attached to the axle. When you run electricity into When you run electricity into this electromagnet, it creates this electromagnet, it creates a magnetic field in the a magnetic field in the armature that attracts and armature that attracts and repels the permanent repels the permanent magnetsmagnets. . So the armature So the armature spins through 180 degreesspins through 180 degrees..To keep it spinning, you have To keep it spinning, you have to change the poles of the to change the poles of the electromagnet.electromagnet.

Commutator and BrushesCommutator and Brushes

Commutator is simply a pair of plates Commutator is simply a pair of plates attached to the axleattached to the axle. . These plates provide These plates provide the two connections for the coil of the the two connections for the coil of the electromagnetelectromagnet. . Commutator and brushes work together to Commutator and brushes work together to let current flow to the electromagnet, and let current flow to the electromagnet, and also to flip the direction that the electrons also to flip the direction that the electrons are flowing at just the right momentare flowing at just the right moment. .

The contacts of the commutator are attached to The contacts of the commutator are attached to the axle of the electromagnet, so they spin with the axle of the electromagnet, so they spin with the magnetthe magnet. . The brushes are just two pieces of The brushes are just two pieces of springy metal or carbon that make contact with springy metal or carbon that make contact with the contacts of the commutatorthe contacts of the commutator..

Spinning ArmatureSpinning Armature

Example of MotorExample of Motor

Your Simple Motor

Timing the on/off cycle for your Armature

This is the Commutator for your Motor