ELECTRIC FIELD SUMMARY
1/26/10
STUDIO
What’s up?
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Reading Assignment – Read all of chapter 18. We
will try to finish all of it (Gauss’s Law) by Friday.
There will be another quiz on Friday covering
through today only.
The next chapter will be on Potential and
Capacitors.
The first exam will follow the conclusion of chapter
19.
Electric Field
The Math
qq0
F k
r2
F
q
F 
k 2
q0
r
A small spherical insulator of mass 4.20 10-2
kg and charge +0.600 µC is hung by a thin
wire of negligible mass. A charge of −0.900 µC
is held 0.150 m away from the sphere and
directly to the right of it, so the wire makes an
angle θ with the vertical.
A tiny ball of mass m carries a charge of
+Q. What electric field (magnitude and
direction) is needed to cause the ball to float
above the ground?
QE
Q
QE  mg
mg
E
Q
mg
The Map
Weak
Strong
C
The map gives the
DIRECTION of E.
Field Lines begin and terminate on
charges. In this case, the terminating
charges are at “infinity”.
We will study this in the next chapter
Back to Work!
Finish E-Field
Potential
Capacitor
EXPERIMENT