1. Magnetic Fields and Magnetic Force
SPH4U

2. Magnetism
Magnetism is an action-at-a-distance force: a magnet creates a magnetic field in the region around it.

3. Magnetic Field
The magnetic field, represented by , is measured in Tesla (T).
The Earth’s magnetic field has a magnitude of approximately 25 – 65 mT.

4. Magnets
Magnets have two poles: North and South. Like poles repel; opposite poles attract.

5. Magnets
Magnetic field lines are drawn out of the North pole and into the South.

6. Permanent Magnets
Ferromagnetic materials (such as iron) are made of tiny magnetic domains that can be induced to align.

7. Electromagnets
A magnetic field can also be generated by moving charge (Oersted’s Principle).

8. Right Hand Rules
The direction of the magnetic field can be determined by Right Hand Rules #1 and 2.

9. Right Hand Rule #1
Point your thumb in the direction of conventional (positive) current flow. Your fingers curl in the direction of the magnetic field lines.

10. Right Hand Rule #2
Curl your fingers in the direction of conventional (positive) current flow around the loop(s). Your thumb points toward magnetic North.

11. Magnetic Force Magnetic fields therefore exert force on moving charge:
speed of charge
angle between velocity vector and magnetic field
charge
magnetic field

12. Magnetic Force
The direction of the force is given by Right Hand Rule #3:
Point your thumb in the direction of the conventional current and your fingers in the direction of the magnetic field.
Your palm pushes in the direction of the magnetic force.

13. Practice
What is the direction of the force on the conductor below?

14. Practice What is the direction of the force on the conductor below?
Left

15. Example
An electron travelling at 4.0 x 106 m/s enters a 0.20 T [into the page] magnetic field as shown below. What is the magnitude and direction of the force on the electron?

16. Example

17. Example
The direction of the force is [down].

18. More Practice “Magnetic Field Mapping Activity” Textbook Questions