Download - Electric Generators and Motors 1 Electric Generators and Motors

Electric Generators and Motors 1

Electric Generators Electric Generators and Motorsand Motors


Introductory QuestionIntroductory Question

If you connect an ordinary electric If you connect an ordinary electric motor in a circuit with a lightbulb, motor in a circuit with a lightbulb, is there a chance that spinning the is there a chance that spinning the motor will cause the lightbulb to motor will cause the lightbulb to light up? light up?

A.A. YesYes

B.B. NoNo


Observations about Electric Observations about Electric Generators and MotorsGenerators and Motors

A generator requires a mechanical A generator requires a mechanical powerpower

A generator provides electric powerA generator provides electric power A motor requires electric powerA motor requires electric power A motor provides mechanical powerA motor provides mechanical power Generators aren’t common in daily Generators aren’t common in daily

lifelife But motors are widely usedBut motors are widely used


4 Questions about Electric 4 Questions about Electric Generators and MotorsGenerators and Motors

How can a moving magnet produce How can a moving magnet produce electricity?electricity?

How can electricity produce a How can electricity produce a moving magnet?moving magnet?

How can a motor operate on DC How can a motor operate on DC power?power?

How can some motors use aluminum How can some motors use aluminum rotors?rotors?


Question 1Question 1

How can a moving magnet produce How can a moving magnet produce electricity?electricity?


Generating ElectricityGenerating Electricity

A changing magnetic fieldA changing magnetic field produces an electric fieldproduces an electric field and can induces current in a conductor.and can induces current in a conductor.

Moving magnets have changing Moving magnets have changing magnetic fieldsmagnetic fields and can propel currents in coils,and can propel currents in coils, so that mechanical power becomes so that mechanical power becomes

electrical power.electrical power.


An AC GeneratorAn AC Generator

An AC Generator resembles a An AC Generator resembles a transformertransformer except that it has no primary coilexcept that it has no primary coil and instead uses a spinning magnetand instead uses a spinning magnet to induce currentto induce current

in the secondary coil.in the secondary coil. Magnet spin rate setsMagnet spin rate sets

AC frequency (60 Hz).AC frequency (60 Hz). Magnet strength andMagnet strength and

coil turns set voltage.coil turns set voltage.



How can electricity produce a How can electricity produce a moving magnet?moving magnet?


An AC MotorAn AC Motor

An AC Generator resembles a An AC Generator resembles a transformertransformer except that it has no secondary coilexcept that it has no secondary coil and instead uses a spinning magnetand instead uses a spinning magnet to extract power fromto extract power from

the primary coil.the primary coil. AC frequency (60 Hz)AC frequency (60 Hz)

sets magnet spin rate.sets magnet spin rate.


Introductory Question Introductory Question (revisited)(revisited)

If you connect an ordinary electric If you connect an ordinary electric motor in a circuit with a lightbulb, motor in a circuit with a lightbulb, is there a chance that spinning the is there a chance that spinning the motor will cause the lightbulb to motor will cause the lightbulb to light up? light up?

A.A. YesYes

B.B. NoNo



How can a motor operate on DC How can a motor operate on DC power?power? Can a motor consist only of permanent Can a motor consist only of permanent

magnets?magnets? Are permanent magnets an endless Are permanent magnets an endless

source of energy?source of energy?


A Permanent Magnet A Permanent Magnet Motor?Motor?

A motor comprised only of permanent A motor comprised only of permanent magnetsmagnets will move as like poles repel and opposites will move as like poles repel and opposites

attractattract and then settle down at minimum potential and then settle down at minimum potential

energy.energy. Unless something alters its poles, that motor Unless something alters its poles, that motor

will never move again.will never move again. Electromagnets operating on DC power Electromagnets operating on DC power

behave like permanent magnets, so DC behave like permanent magnets, so DC alone can’t keep a motor turning for long.alone can’t keep a motor turning for long.


A DC MotorA DC Motor

Switches can reverse a motor’s polesSwitches can reverse a motor’s poles so that a DC motor with switches can work!so that a DC motor with switches can work! The simplest switch system is a commutator,The simplest switch system is a commutator, which reverses the magnetic poles whenever which reverses the magnetic poles whenever

the motor approaches minimum potential the motor approaches minimum potential energy.energy.

Its commutator allowsIts commutator allowsa DC motor to turna DC motor to turnendlessly.endlessly.



How can some motors use aluminum How can some motors use aluminum rotors?rotors? Aluminum is nonmagnetic, so how can Aluminum is nonmagnetic, so how can

it work?it work?


The Lorentz ForceThe Lorentz Force

A charge moving through a magnetic A charge moving through a magnetic fieldfield experiences the Lorentz force, experiences the Lorentz force, a force that pushes it perpendicular to its a force that pushes it perpendicular to its

velocityvelocity and perpendicular to the magnetic field:and perpendicular to the magnetic field:

Lorentz force = charge· velocity· magnetic Lorentz force = charge· velocity· magnetic field· sine(angle)field· sine(angle)

where the “angle” is that betweenwhere the “angle” is that betweenthe velocity and the magnetic field.the velocity and the magnetic field.


Induction and Lorentz Induction and Lorentz ForceForce

When a magnetic field moves past a When a magnetic field moves past a conductor,conductor, it induces current in that conductorit induces current in that conductor and that current experiences the Lorentz force.and that current experiences the Lorentz force.

The current and conductor experience a The current and conductor experience a forceforce that pulls them with the moving magnetic field.that pulls them with the moving magnetic field.

A moving magnet tends to drag metals with A moving magnet tends to drag metals with it.it.

This effect can be used to make a motor.This effect can be used to make a motor.


AC Induction MotorAC Induction Motor

Stationary AC electromagnets can produce Stationary AC electromagnets can produce a magnetic field that circles a conducting a magnetic field that circles a conducting rotor.rotor.

Currents induced in that rotorCurrents induced in that rotor experience the Lorentz forceexperience the Lorentz force and are pushed along with the rotating field.and are pushed along with the rotating field.

The rotor spins almost as fast as the field The rotor spins almost as fast as the field circles.circles.

This system is known as an AC induction This system is known as an AC induction motor.motor.


Summary about Electric Summary about Electric Generators and MotorsGenerators and Motors

Generators using moving magnets to Generators using moving magnets to turn mechanical power into electrical turn mechanical power into electrical powerpower

Motors use moving magnets to turn Motors use moving magnets to turn electrical power into mechanical powerelectrical power into mechanical power

Induction motors depend on the Induction motors depend on the Lorentz force to allow electromagnets Lorentz force to allow electromagnets to spin a nonmagnetic metal rotor.to spin a nonmagnetic metal rotor.

Download - Electric Generators and Motors 1 Electric Generators and Motors

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