1. Magnetism & Electromagnetic Induction

2. What causes magnetism? Electrons in motion create a magnetic field.
Electrons move in current, and also within individual atoms
ALL magnetism comes originally from the movement of charged particles.

3. Magnets Magnets have “polarity” There are two types of magnets:
Always two poles: north and south
Comes from magnetic domains
Like poles repel and unlike poles attract.
There are two types of magnets:
Permanent magnets – domains are always aligned
Temporary magnets – formed when iron-bearing metals are brought near a magnetic field and their domains temporarily align

4. The Magnet Man… Nikola Tesla
Inventor and electrical engineer
Widely famous for his work on AC circuits
Pioneered wireless energy transfer to power electrical devices as early as 1873
His unfinished “Wardenclyffe Tower” Project was meant to supply industrial power wirelessly on an international basis
Fought with Edison for years, over AC vs. DC
Tesla vs. Edison

5. Magnetic Fields
Match the diagrams with the magnetic fields below.

6. Magnetic field - the space around a magnet over which the magnetic force exists
The more field lines, the stronger the magnetic field
Field lines ALWAYS point from north to south
Magnetic Field strength is measured in Teslas (T)

7. Direction of Magnetic Field
The direction is the same as where the north pole of a compass points when it is placed in the magnetic field.
So, field lines come out of the magnet at its north pole and enters at its south pole.
Magnetic field lines are most concentrated at the poles (the field is stronger at the poles)
Remember… opposites attract, likes repel!

8. Draw the magnetic field lines below.

9. Draw the magnetic field lines below.

10. Electromagnets
Electromagnets – devices that use electric current to produce a concentrated magnetic field
Iron in a coil of current carrying wire will become an electromagnet.
Temporary magnets
Some uses: telephone relays,
levitation, magnetic cranes,
sorting metal, MRI

11. Electromagnetism
Christian Oersted discovered that electric current in a wire creates a magnetic field.
Current, moving in a straight
wire, produces a magnetic
field surrounding the wire.
We can see this with a compass...
But, since the field goes around the wire, how do we know which way it goes?

12. The Right Hand Rules (RHR)
Rules to help you determine magnetic field direction, using your RIGHT hand.
First RHR – current in a straight wire
Grasp the wire with your right hand.
Thumb is in the direction of the positive current.
Fingers circle the wire and point in the direction of the magnetic field (circular).

13. We Use Two RHRs: (there are actually three)
First RHR: current in a straight wire
Grasp the wire with your right hand.
Point thumb in the direction of the current
Fingers circle the wire and point in the direction of the magnetic field (circular)
Second RHR: current in a coiled wire
Grasp the coil with your right hand.
Curl fingers around the loops of wire in the direction of the current
Thumb points toward the NORTH pole of the electromagnet

14. 1st RHR
Note: current traveling in opposite directions in a wire, will have magnetic fields in opposite directions

15. 2nd RHR

16. More on Electromagnetism
Loops of wire produce stronger electromagnets than straight wire
The more loops of wire, the stronger the field
Thicker wire produces a stronger magnet

17. Using the RHRs Use right hand rules to draw the magnetic field lines.
The “dot” means current is coming out of the page
The “x” means current is going into the page

18. Electromagnetic Induction
Faraday’s Discovery:
Faraday found he could induce current by moving a wire in a magnetic field.
If the wire moves up through the field the current moves in one direction.
If the wire moves down through the field the current moves in the opposite direction.
If the wire moves parallel to the field lines no current is produced.
Electromagnetic Induction: the process of inducing current in a wire due to the relative motion of the wire and/or the magnetic field

19. Electromagnetic Induction
Observing Faraday’s Experiment:
Faraday’s Experiment 1
Faraday’s Experiement 2

20. Electric Generators Convert mechanical energy to electrical energy
How it works:
Mechanical energy turns an armature
armature: wire wrapped around an iron core in a magnetic field
The induced voltage causes current to flow.
A generator at work

21. Electric Generator
The strength & direction of induced current changes as the armature rotates
Induced current is maximum when the wire loops move through the strongest areas of the magnetic field

22. Alternating Current (AC) Generators
The direction of the current switches back and forth at some frequency
The faster the coil turns, the faster the directions changes, so the higher the frequency.
Let’s Look

23. Is it AC or DC? Wall plugs provide AC, batteries provide DC
Electricity transmission systems (grids) are AC, but operate on different frequencies
Five in the U.S. alone
Why you can’t plug your stuff directly into the wall in Europe
High-Voltage DC can connect AC systems running on different frequencies

24. Motor vs. Generator What’s the difference?
Motor: Electrical to Mechanical Energy
Generator: Mechanical to Electrical Energy
Can sometimes be used interchangeably, like in a vehicle
Motor when accelerating – battery provides energy to run motor
Generator when braking – inertia used to recharge battery

25. Transformers Used to change AC voltage
Very efficient (little energy lost to heat)
How they work:
two coupled coils are attached using a metal bar (usually a ring or “U”)
the coils have different numbers of loops
One is the primary coil
The other is the secondary coil

26. Types of Transformers: Step-Up or Step-Down
More turns (loops) in the SECONDARY coil
The secondary voltage is greater than the primary voltage
Step-Down:
More turns (loops) in the PRIMARY coil
The primary voltage is greater than the secondary voltage