1. Foundations of Physical Science
Unit 3: Electricity and Magnetism

2. Chapter 10: Magnets and Motors
10.1 Permanent Magnets
10.2 Electromagnets
10.3 Electric Motors and Generators

3. Learning Goals Describe the properties of a permanent magnet.
Describe the forces that magnets exert on other.
Explain why materials like iron and steel are attracted to magnets.
Explain why a compass points north.
Build an electromagnet.
Analyze how electric current affects the strength of the magnetic field in an electromagnet.
List three ways that the strength of an electromagnet can be increased.
Compare permanent magnets and electromagnets.
List several applications of electromagnets.
Explain electromagnetic induction.
Describe how electric motors and generators work.

4. Vocabulary electromagnet electromagnetic induction generator magnet
magnetic field intensity
magnetic force
permanent magnet
south pole

5. Permanent Magnet
A material that keeps its magnetic properties, even when it is not close to other magnets
alnico
ferrite
lodestone
Bar magnets
Refrigerator magnets
Horseshoe magnets

6. Ferromagnets
Materials that are attracted to nearby magnets but do not show magnetism otherwise
“Domains” become aligned in the presence of a permanent magnet
iron
steel
nickel
cobalt

8. Properties of Magnets Have two opposite poles. north south
Magnets exert forces on each other.
Forces depend on the alignment of the poles.

9. Magnetic Forces & Electrical Forces
Similarities
Objects attract and repel
Act between objects that are not touching
Strength of force depends on distance between the objects
Differences
Electric charges produce electrical forces
Magnetic poles produce magnetic forces
Magnetic forces cannot be isolated

10. Magnetic Forces Break a Magnet
Each half still behaves as a complete magnet
Even a piece 1 atom thick has two poles
Atoms are magnets!
A north magnetic pole never exists without the company of a south pole, and vice versa
The north and south poles of a magnet are like the head and tail of the same coin

11. Discovery and Use of Magnetism
Lodestone: magnetic properties
Greeks created the compass
Chinese created the “south pointer”
By 1200 explorers from Italy were using the compass to guide ocean voyages beyond the site of land
By the 1400 the Chinese were using compasses to travel to Africa
The compass led to the interactions amongst cultures!

12. How does a compass work?
The origins of the terms “north pole” and “south pole” of a magnet come from the direction that a magnetized compass needle points
Pointing north  north pole
Pointing south  south pole
The north pole of the compass needle must point north because it is attracted by the south pole of another magnet. Where is this other magnet???

13. How does a compass work? It is EARTH!!!!
Compass needle swings toward the geographical north pole
…or the magnetic south pole!

14. The Magnetic Field The force between two magnets
Every magnet creates an energy field, called the magnetic field, in the space around it
The field exerts forces on any other magnet that is within its range, the magnetic force

16. Michael Faraday Born in 1791 London book-binder turned scientist
Invented early motors using electromagnets

17. Magnetic Field Around a Current-Carrying Wire
A magnetic field is produced by:
A single moving charge
A current of charges
Demonstrated with compasses around the wire

19. Magnetic Field Around a Current-Carrying Wire
More loops means more magnetic field intensity
Current-carrying coil of many loops = strong magnetic field intensity

20. Electromagnet A magnet created when electric current flows in a wire
The simplest electromagnet uses a coil of wire, wrapped around iron
Because iron is magnetic, the magnetic field is concentrated in the current in the coil

21. Electromagnets
Can switch north and south pole by reversing the direction of the current
Advantage over permanent magnets
Right Hand Rule

23. Electromagnet A common sight in junk yards
Strength is limited by overheating of the current carrying-coils
The most powerful ones omit the iron core and use superconducting coils

24. Increase Strength: Electromagnet
Increase the current
Increase the voltage (add a battery)
Add more turns of wire around the nail (but this increases resistance & generates more heat)

25. Forces in an Electromagnet Depend on…
Amount of electric current in the wire
Amount of iron or steel in the core
The number of turns in the coil

26. Electric Motors
A device that uses a current-carrying coil forced to rotate in a magnetic field
Electrical Energy  Mechanical Energy

27. Using Magnets to Spin a Disk
Use a single magnet to attract and repel magnets in a rotor by flipping its poles.

28. Using Electricity to Reverse the Magnet
Commutator: the switch that reverses the poles

29. Electromagnetic Induction
If you move a magnet through a coil of wire, then electric current is created
The moving magnet induces electric current to flow
The current stops if the magnet stops moving

31. Electromagnetic Induction
Voltage is caused, or induced, by the relative motion between a wire and a magnetic field
No battery or other voltage source is needed
The greater the number of loops of wire moving in a magnetic field the greater the induced voltage
Current is proportional to the number of loops

32. Faraday’s Law
The induced voltage in a coil is proportional to the number of loops multiplied by the rate at which the magnetic field changes within those loops

33. Generating Electricity
Generator: a combination of mechanical and electrical systems that converts kinetic energy into electrical energy
Power plans use generators
The magnetic field alternates north to south as the disk spins-thus, generators produce AC

34. Generating Electricity
A power plant generator contains a turbine that turns magnets inside loops of wire to generate electricity.

35. Motors and Generators Motor: Generator:
Electrical energy: input
Mechanical energy: output
Generator:
Mechanical energy: input
Electrical energy: output
Both devices transform energy from one form to another