1. Magnets and Magnetic Fields

2. Magnetic Field Lines Never will intersect with each other or cross Always directed away from the north pole and towards the south pole of a magnet Strongest field where the lines are closest together

3. Magnetic Force on a Current An electric field in a wire moves the electrons through the wire and generates a current The moving electrons react to the presence of an external magnetic field: o F = Force (N) o I = current (A) o L = length of wire within the magnetic field (m) o B = Magnetic Field Strength (T) o  = Angle between the current and the magnetic Field

4. Right-Hand Rule (a) To determine the direction of the force that a current-carrying wire experiences when placed in an existing magnetic field: o Thumb = direction of current o Pointer finger = direction of field o Middle finger = direction of force

5. Sample problem: A 12.5 cm long wire with a current of 0.505 A is placed in a uniform magnetic field of strength 0.850 T. If the current is running towards the right, and the magnetic field is directed into the page (away from you), what is the force it experiences (magnitude and direction)?

6. Magnetic Force on a Moving Charge Currents are made of many, many multiple moving charges. Single charged particles that are moving ALSO experience a force: o F = Force (N) o q = charge (C) o v = velocity of the moving charge (m·s -1 ) o B = Magnetic Field Strength (T) o  = Angle between the charge’s path and the magnetic Field

7. Right-Hand Rule (b) Same as the rule for a current-carrying wire in a magnetic field, with the following modification: The “current” becomes the direction of the moving positive test charge

8. What happens when… A charged particle enters a magnetic field? In what direction is the force? What does the path become?

9. Ørsted’s Discovery

10. Magnetic Field Strength Tidbits of Tesla-related trivia The field strength of the Earth at its surface is ~ 10 -4 T A wire carrying 2000A produces a magnetic field of 8 x 10 -5 T 5 m from the wire!

11. Force BETWEEN two current-carrying wires L = length of the wires (m) r = distance separating the two wires (m) I = current in the wire  0 = magnetic permeability of the vacuum Assumption is that the wires are parallel to each other

12. Magnetic Field Patterns Around 2 wires with currents in the SAME direction: