1. what can you do with Magnetic Field and where does it come from!
W10D1
November 1, 2010
what can you do with Magnetic Field and where does it come from!

2. This week Mostly magnetism and effects on and from currents.
There is a new WA posted and another may be added at any time.
Quiz on Friday
Next examination is looming! keep up with the work.

3. PROBLEM Redux – review direction issue.
Magnetism
PROBLEM Redux – review direction issue.
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

4. Assume B into the page
vB is to the left F
But q is negative and force
will go the other way.
Which is what we want!
B is as assumed! +

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

6. 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

7. magnetic Field of a wire carrying a current
Not the same B!!

8. two wires again D

9. Some useful Equations not derived in the text
Field a distance r from a wire
Field at the center of a loop
of wire with N turns
Field inside a solenoid with n
turns per unit length

10. talk about torque
Current Loops in Magnetic Fields

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

12. 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

13. 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

14. N Turns of Wire
t=NiABSin(q)
N Turns

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

16. motor
MANY TURNS
OF WIRE
Motors are usually AC

17. generator