1. Aim: How can we explain the 3 rd left hand rule of magnetism? Do Now: How will the current flow? To the left

2. 3 rd Left-Hand Rule  Used any time you have a charge moving through a magnetic field.  When current is placed perpendicular to magnetic field, a force will be produced on the wire.

4.  Place thumb in direction of current, and fingers pointing in direction of magnetic field. Your palm will point in the direction the force pushes.

5. Current N S Which direction is the force? Up

6. Describe the motion of the moving charge  To figure out the force on a positive charge, use the right hand (or opposite from negative charges)  This is how Jay can smash particles together  http://www.youtube.com/watch?v=bEvLK 11jdJ8  The resultant of the velocity and the force can produce circular motion

7. Remember…  Moving charges create magnetic fields.  Your left-hand rules  These concepts revolutionized the world

8. Force on a Current Carrying Wire F = I l xB F = I l xB F = force (N) I = electron flow (A) l = length of wire (m) B = Magnetic Field strength (Tesla = T = N/Am) **The x is a cross product – this means the wire and field must be perpendicular to use this formula

9. Example Problem The current flowing in a 2.0 m wire is 100 A. The wire is placed in a magnetic field of 3.0 x 10 -3 T such that it is oriented perpendicular to the field. Calculate the force experienced by the wire. F = I l xB F = 100 A(2.0 m)(3.0 x 10 -3 T ) F = 0.6 N

10. Force on an Electron An electron entering a magnetic field experiences a force similar to that on a wire (proton would go in the opposite direction). Since F = I l B and I = q/t Then, F = q l B/t,and l /t = v Then the force on any charged particle is F = qvB

11. Mass of an Electron Since a particle is free to move, upon entering a magnetic field, it will constantly change directions in response to the force so, it goes in a circle x x x x x x x x x e-e- x x x x x x x x x p

12. Mass of an Electron Because the electron moves in a circular path the force can also be considered a centripetal force, so F = qvB = mv 2 /r Therefore, q/m = v/Br  1897: charge to mass ratio (q/m) was determined by J.J. Thomson  1909-1913: charge of an electron was determined by Millikin with his oil drop experiment  Mass of electron was then determined with q/m

13. S N Axis of rotation What will happen? Fingers – field Thumb – current Palm – force x x x x x The wire will spin This is a motor

14. Electric Motor Converts electrical energy to mechanical energy Motor Demo

15. S N Axis of rotation What will happen? Fingers – field Palm – force Thumb - current x x x x x Current will be generated This is a generator

16. Generator Converts mechanical energy to electrical energy Generator Demo

17. AURORAS  Known as the northern lights  Electrons from violent storms on the Sun enter the Earth’s magnetic field  The electrons collide with gases in the Earth’s atmosphere  Color depends on the type of atoms and molecules struck Proton Aurora Forms from Reconnection Event This is what is happening This is what you see