A Kingdom for a Magnetic Field!

1. A Kingdom for a Magnetic Field! W9D3 October 27, 2010

2. Next few days • Today • QUIZ • Some Magnetic Forces Forces • Unit on Forces • Don’t forget the WA that is due Sunday night. • Study Session Monday.

3. Let’s Click • A charged particle enters a uniform magnetic field and follows the circular path shown in the drawing. • The charge on the particle is: • A Positive • B Negative • C Neutral • D North • E South

4. What happens when a charge enters a magnetic field that is perpendicular to its velocity?

5. Look at the direction of the force and the velocity

8. PROBLEM • An electron at point A in the figure has a speed v0 of 1.4 x 106 m/s. Find • the magnitude and direction of the magnetic field that will cause the electron to follow the semicircular path from A to B and • the time required for the electron to move from A to B. m=9.1E-31 Kg e=1.6E-19 C

9. Off Angle P

10. Force And Wires The magnetic force on the moving charges pushes the wire to the right. Why??

12. Same Thing but angular:

13. Consider TWO wires • The two wires will • A Attract • B Repel • C Neither of the above • D Insufficient Information I I xxx xxx xxx xxx v F X B

14. Let’s talk about torque Current Loops in Magnetic Fields

15. Current Loop What is force on the ends?? Loop will tend to rotate due to the torque the field applies to the loop.

16. pivot The Loop (From the top) OBSERVATION Force on Side 2 is out of the paper and that on the opposite side is into the paper. No net force tending to rotate the loop due to either of these forces. The net force on the loop is also zero,

17. The other sides t1=F1 (b/2)Sin(q) =(B i a) x (b/2)Sin(q) total torque on the loop is: 2t1 Total torque: t=(iaB) bSin(q) =iABSin(q) (A=Area)

18. Application: The motor • If the conductor is a loop, the torque can create an electric motor.

20. Unit #12 Start your engines

21. STOP