1. ELECTRICITY & MAGNETISM

2. Objectives: After completing this module, you should be able to:
Provide evidence that fields exist between objects exerting forces on each other even thogh the objects are not in contact

3. Magnetism
Since ancient times, certain materials, called magnets, have been known to have the property of attracting tiny pieces of metal. This attractive property is called magnetism. N S
Bar Magnet N S

4. Magnetic Poles S N
Iron filings
The strength of a magnet is concentrated at the ends, called north and south “poles” of the magnet. N S E W
Compass
Bar magnet
A suspended magnet: N-seeking end and S-seeking end are N and S poles.

5. Magnetic Attraction-Repulsion
Magnetic Forces: Like Poles Repel
Unlike Poles Attract

6. Magnetic Field Lines
We can describe magnetic field lines by imagining a tiny compass placed at nearby points. N S
The direction of the magnetic field B at any point is the same as the direction indicated by this compass.
Field B is strong where lines are dense and weak where lines are sparse.

7. Magnetic Field The area in which magnetic forces act
The magnetic field is strongest near the poles

8. Field Lines Between Magnets
Unlike poles N S
Attraction
The magnetic fields combine to form a stronger field between the magnets when unlike poles are near each other and a weaker field when like poles are near each other
Leave N and enter S N
Repulsion
Like poles

9. Properties of a Magnet Attract or repel other magnets
When allowed to swing freely one end will point magnetic north
Attract iron

10. But in a magnet or a metal, we can line up to become magnetic
MAGNETISM
Invisible force of “push” or “pull” by an object with this property
Hi! We’re e- (electrons)!!! We usually speed around the outside of the nucleus
In these atoms, each e- is going its own way
Wagon does not move; forces are not lined up
Wagon moves; forces are lined up
But in a magnet or a metal, we can line up to become magnetic
Lined up atoms/ electrons=Domain

11. Inside a magnet -The smallest particle of an element is an atom
-Atoms contain positively (protons) and negatively (electrons) charges particles
Spinning electrons produce magnetic fields
In magnets, the spinning electrons are aligned in domains that are in the same direction

12. MAGNETS Materials whose atoms can be aligned
Elements that can be magnetic
Fe: Iron soft iron loses magnetism easily
Co: Cobalt used to harden tools
Ni: Nickel used to make jewelry
Other magnets:
Compass
Earth

13. MAGNETS Domains Have domain (lined up atoms)
Have polarity (characteristic of magnetism) North-seeking pole (“normal”) South-seeking pole (“reversed”)
Cannot have only 1 pole *** magnetic poles cannot be isolated***
Like poles repel; Opposite poles attract

14. MAGNETIC FIELDS
An area where the force exists; area where force is felt
Magnetic field lines
Leaves north pole & enters south pole
Lines closer together = stronger field
NOTICE
Strongest at the poles
Field lines start at the NORTH pole and travel towards the SOUTH pole

15. Temporary Magnets
Some materials like steel or iron can be easily magnetized, but lose their magnetism quickly. A magnet that easily loses its magnetism is called a temporary magnet

16. Earth is a Magnet
A compass will point to magnetic north because a compass needle has a magnetized needle that spins freely.

17. Destroying Magnets
When the magnetic domains are forced out of alignment, magnets will be destroyed. This can happen by heat or even a violent strike to a magnet with a hammer

18. ELECTROMAGNET Electromagnetism
A magnet with a field produced by an electric current
Electromagnetism
a moving charge (electricity) produces a magnetic field
More coils of wire= more current = stronger magnet
Bigger battery/stronger current = stronger magnet
What’s going on? An electromagnet is a magnet that can be turned on and off. In this experiment, the battery is a source of electrons. When you connect the wire to the battery, the electrons flow through the wire. If there is not a complete circuit, the electrons will not flow. Electrons behave like little magnets and when they flow through a wire, they create a magnetic field, which turns the nail into a magnet that can pick up paper clips and staples!

19. Solenoids
The magnetic field produced by a current has three distinct characteristics:
the field can be turned on/off
have its direction reversed
have its strength changed.
Solenoid: A coil of wire with a current. The two ends act like magnetic poles
A solenoid with a ferromagnetic core is an electromagnet

20. ELECTRIC FIELDS
A force field that fills the space around electrical charges
Electrical field
two charges are separated
vectors (lines of force) point towards negative charges and away from positive charges
strength of field (magnitude)= distance between two charges
closer particles = stronger field

21. CONDUCTORS
A material, usually a metal, through which electrons can flow
good conductor electrons able to move freely within the atoms of the material
poor conductor or insulator electrons are not free to move about the atoms of the other material

22. ELECTRIC CIRCUIT
A path that allows electrons to flow from negative to positive

23. ELECTRICITY  MAGNETISM
Electric currents cause magnetism
How can you tell? Compass needle moves when near electrical current - creating an magnetic field

24. MAGNETISM  ELECTRICITY
Moving magnet can generate electricity
How can you tell? Electromagnetic induction
moving a magnet in and out of a coiled wire created an electrical current without a battery

25. Increasing the Strength of electromagnets
1. increase the current in the solenoid
Add more loops of wire to the solenoid
Use a stronger ferromagnetic material