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Unformatted text preview: charged conductors:
+Q y d σ
εo E x -Q What is σ ??
A = area of plate Second, integrate E to find the potential difference V
d d 0 V = − ∫ E ⋅ dy d 0 V = − ∫ (− Edy) = E ∫ dy = 0 Q
εo A As promised, V is proportional to Q !! 12 Q
V Qd / ε o A C= ε0 A
d C determined by
Physics 212 Lecture 7, Slide 12
Physics Question Related to Preflight
Initial charge on capacitor = Q0 BB d
+Q1 Insert uncharged conductor
Charge on capacitor now = Q1 d t
- Q1 How is Q1 related to Q0 ??
A. Q1 < Q0
B. Q1 = Q0
C. Q1 > Q0
14 Plates not connected to anything CHARGE CANNOT CHANGE !!
Physics 212 Lecture 7, Slide 13
Physics Where to Start??
d t BB - Q0
What is the total charge induced on the bottom surface of the conductor? A.
E. 17 +Q0
Positive but the magnitude unknown
Negative but the magnitude unknown Physics 212 Lecture 7, Slide 14
Physics WHY ??
E - Q0
- Q0 WHAT DO WE KNOW ??? E must be = 0 in conductor !! Charges inside conductor move to cancel E field from top & bottom plates 19 Physics 212 Lecture 7, Slide 15
Physics Calculate V
y Now calculate V as a function o...
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