1. What we’ll need for today…
Magnets (bar and horseshoe)
Iron filings
Compasses
Two wires, 4 batteries in series, light bulb
Electromagnets (solenoids)

2. James Clerk Maxwell
Michael Faraday
Electromagnetism

3. Magnets: What do you know?
Think pair share

4. Magnets – Key Points
Have poles (N and S) rather than + and – for charges
Like poles repel; Opposite poles attract
Produce a magnetic field: B
similar to gravitational field: g
and electric field: E
Magnetic Flux refers to the density of field lines
The Tabletop Explainer…

5. Magnetic Field (B) Vector quantity (arrows)
Points in direction a compass would point
Runs from North to South
Allows for FM: Magnetic Forces (the reason a compass needle moves!)

7. Where does the electro come in?
Current carrying wire….

8. Current carrying wire…
A static distribution of charges produces an electric field
Charges in motion (an electrical current) produce a magnetic field

9. 1st RHR A moving electric charge produces a magnetic field
Thumb: Direction of Current
Fingers: Curl in direction of magnetic field

10. What happens then…..
If we have a whole bunch of current carrying wire wrapped tightly?

11. Electromagnets
Arranging wire in a coil and running a current through produces a magnetic field that looks a lot like a bar magnet

12. Solenoid (electromagnet)
The 2nd RHR:
Fingers: Direction of current through solenoid
Thumb: Points to north pole
Cross section:

13. Magnetic fields inside a solenoid
B = µo I n B: Magnetic Field Strenth (Tesla T) µo : Permeability of free space = 4π x 10-7 T·m/A I: Current (Amperes A) n: Loops per meter = N/l N: total loops l: length

14. Example
A hollow solenoid is 25 cm long and has 1000 loops. If the solenoid has a diameter of 4.0 cm and a current of 9.0 A what is the magnetic field in the solenoid?

15. 3rd RHR Applies to: Charges moving in a magnetic field
A current carrying wire in a magnetic field

16. Cross Product
Cross product: Vector product of two vectors. Gives a new vector that is orthogonal (perpendicular) to both

17. 3rd RHR
Direction: Thumb: current/particle motion Fingers: Magnetic Field direction Force: Palm (positive); Knuckle (negative) Mass spectrometer

18. 3rd RHR
For a charge moving in a magnetic field, a magnetic force is applied to it. FM = q v x B (cross product) For us… FM = qvBsinθ q: charge v: velocity B: Magnetic Field strength θ: orientation

19. Example A proton is fired into a magnetic field as follows: Find/show:
It’s path FM
Radius of it’s path

20. 3rd RHR
For a current carrying conductor, the magnetic force is as follows: FM = B I l sin θ If the conductor is perpendicular to the magnetic field: FM = BIl B: Magnetic Field strength (T) I: Current (A) l: length of conductor (m) θ: orientation

21. 3rd RHR
For a current carrying wire in a magnetic field, a magnetic force is applied to it. FM = B I L sinθ B: Magnetic Field strength I: current L: Length of wire in magnetic field θ: orientation