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

2. Next few days Today Unit on Forces
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
Magnetism

6. Magnetism

7. Magnetism

8. PROBLEM
An electron at point A in the figure has a speed v0 of 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
Magnetism

9. Off Angle P
Magnetism

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 I I B Repel
C Neither of the above
D Insufficient Information I I
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.
Magnetism

16. 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,
pivot
Magnetism

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)
Magnetism

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