A ve0d b ve0dt c ve dt y the integral area under

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Unformatted text preview: tart?? +Q0 d t -Q0 What is the total charge induced on the bottom surface of the conductor? A.. A B. C. D. E. 17 +Q0 ­Q0 0 Positive but the magnitude unknown Negative but the magnitude unknown BB WHY ?? WHY ?? +Q0 -Q0 +Q0 +Q E E=0 E -Q0 WHAT DO WE KNOW ??? E must be = 0 in conductor !! Charges inside conductor move to cancel E field from top & bottom plates Charges inside conductor move to cancel E field from top & bottom plates 19 Calculate V y Now calculate V as a function of distance from the bottom V ( y ) = − E ⋅ dy ∫ conductor. 0 d +Q0 y E t y -E0 d E=0 t V -Q0 21 What is ∆ V = V(d)? A) ∆ V = E0d B) ∆ V = E0(d – t) C) ∆ V = E (d + t) y The integral = area under the curve BB Back to Preflight 10 Back to Preflight 10 BB What have we learned? C0 = Q0/V0 = ε0A/d If charges are the same Q1 = Q0 V0 = E0d V1 = E0(d – t) 50 40 Preflight Results 30 20 10 0 What do these results tell us about how C1 is related to C0 ?? Back to Preflight 10 Back to Preflight 10 BB Same V: What is Q1 interms of Q0? Leave as exercise! We can determine C from either case same V (preflight) same Q (lecture) E0 = Q0/ε0A C depends only on geometry !! Same Q: V0 = E0d C0 = Q0/E0d V1 = E0(d – t) C1 = Q0/(E0(d – t)) C0 = ε0A/d C1 = ε0A/(d – t) Energy in Capacitors BANG BANG 31 cross-section a4 a3 Calculation Calculation A capacitor is constructed from two conducting cylindrical shells of radii a1, a2, a3, and a4 and length L (L >> ai). a2 a1 metal What is the capacitance C of this device ? metal • Conceptual Analysis: Q C≡ But what is Q a n d wh a t is V? T h e y a re no t g ive n? ? V • Important Point: C...
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