1. Electric Generators and Motors 1 Electric Generators and Motors

2. Electric Generators and Motors 2 Introductory Question If you connect an ordinary electric motor in a circuit with a lightbulb, is there a chance that spinning the motor will cause the lightbulb to light up? If you connect an ordinary electric motor in a circuit with a lightbulb, is there a chance that spinning the motor will cause the lightbulb to light up? A. Yes B. No

3. Electric Generators and Motors 3 Observations about Electric Generators and Motors A generator requires a mechanical power A generator requires a mechanical power A generator provides electric power A generator provides electric power A motor requires electric power A motor requires electric power A motor provides mechanical power A motor provides mechanical power Generators aren’t common in daily life Generators aren’t common in daily life But motors are widely used But motors are widely used

4. Electric Generators and Motors 4 4 Questions about Electric Generators and Motors How can a moving magnet produce electricity? How can a moving magnet produce electricity? How can electricity produce a moving magnet? How can electricity produce a moving magnet? How can a motor operate on DC power? How can a motor operate on DC power? How can some motors use aluminum rotors? How can some motors use aluminum rotors?

5. Electric Generators and Motors 5 Question 1 How can a moving magnet produce electricity? How can a moving magnet produce electricity?

6. Electric Generators and Motors 6 Generating Electricity A changing magnetic field A changing magnetic field produces an electric field produces an electric field and can induces current in a conductor. and can induces current in a conductor. Moving magnets have changing magnetic fields Moving magnets have changing magnetic fields and can propel currents in coils, and can propel currents in coils, so that mechanical power becomes electrical power. so that mechanical power becomes electrical power.

7. Electric Generators and Motors 7 An AC Generator An AC Generator resembles a transformer An AC Generator resembles a transformer except that it has no primary coil except that it has no primary coil and instead uses a spinning magnet and instead uses a spinning magnet to induce current in the secondary coil. to induce current in the secondary coil. Magnet spin rate sets AC frequency (60 Hz). Magnet spin rate sets AC frequency (60 Hz). Magnet strength and coil turns set voltage. Magnet strength and coil turns set voltage.

8. Electric Generators and Motors 8 Question 2 How can electricity produce a moving magnet? How can electricity produce a moving magnet?

9. Electric Generators and Motors 9 An AC Motor An AC Generator resembles a transformer An AC Generator resembles a transformer except that it has no secondary coil except that it has no secondary coil and instead uses a spinning magnet and instead uses a spinning magnet to extract power from the primary coil. to extract power from the primary coil. AC frequency (60 Hz) sets magnet spin rate. AC frequency (60 Hz) sets magnet spin rate.

10. Electric Generators and Motors 10 Introductory Question (revisited) If you connect an ordinary electric motor in a circuit with a lightbulb, is there a chance that spinning the motor will cause the lightbulb to light up? If you connect an ordinary electric motor in a circuit with a lightbulb, is there a chance that spinning the motor will cause the lightbulb to light up? A. Yes B. No

11. Electric Generators and Motors 11 Question 3 How can a motor operate on DC power? How can a motor operate on DC power? Can a motor consist only of permanent magnets? Can a motor consist only of permanent magnets? Are permanent magnets an endless source of energy? Are permanent magnets an endless source of energy?

12. Electric Generators and Motors 12 A Permanent Magnet Motor? A motor comprised only of permanent magnets A motor comprised only of permanent magnets will move as like poles repel and opposites attract will move as like poles repel and opposites attract and then settle down at minimum potential energy. and then settle down at minimum potential energy. Unless something alters its poles, that motor will never move again. Unless something alters its poles, that motor will never move again. Electromagnets operating on DC power behave like permanent magnets, so DC alone can’t keep a motor turning for long. Electromagnets operating on DC power behave like permanent magnets, so DC alone can’t keep a motor turning for long.

13. Electric Generators and Motors 13 A DC Motor Switches can reverse a motor’s poles Switches 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 the motor approaches minimum potential energy. which reverses the magnetic poles whenever the motor approaches minimum potential energy. Its commutator allows a DC motor to turn endlessly. Its commutator allows a DC motor to turn endlessly.

14. Electric Generators and Motors 14 Question 4 How can some motors use aluminum rotors? How can some motors use aluminum rotors? Aluminum is nonmagnetic, so how can it work? Aluminum is nonmagnetic, so how can it work?

15. Electric Generators and Motors 15 The Lorentz Force A charge moving through a magnetic field A charge moving through a magnetic field experiences the Lorentz force, experiences the Lorentz force, a force that pushes it perpendicular to its velocity a force that pushes it perpendicular to its velocity and perpendicular to the magnetic field: and perpendicular to the magnetic field: Lorentz force = charge· velocity· magnetic field· sine(angle) where the “angle” is that between the velocity and the magnetic field.

16. Electric Generators and Motors 16 Induction and Lorentz Force When a magnetic field moves past a conductor, When a magnetic field moves past a conductor, it induces current in that conductor it 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 force The current and conductor experience a force that pulls them with the moving magnetic field. that pulls them with the moving magnetic field. A moving magnet tends to drag metals with it. A moving magnet tends to drag metals with it. This effect can be used to make a motor. This effect can be used to make a motor.

17. Electric Generators and Motors 17 AC Induction Motor Stationary AC electromagnets can produce a magnetic field that circles a conducting rotor. Stationary AC electromagnets can produce a magnetic field that circles a conducting rotor. Currents induced in that rotor Currents induced in that rotor experience the Lorentz force experience 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 circles. The rotor spins almost as fast as the field circles. This system is known as an AC induction motor. This system is known as an AC induction motor.

18. Electric Generators and Motors 18 Summary about Electric Generators and Motors Generators using moving magnets to turn mechanical power into electrical power Generators using moving magnets to turn mechanical power into electrical power Motors use moving magnets to turn electrical power into mechanical power Motors use moving magnets to turn electrical power into mechanical power Induction motors depend on the Lorentz force to allow electromagnets to spin a nonmagnetic metal rotor. Induction motors depend on the Lorentz force to allow electromagnets to spin a nonmagnetic metal rotor.