nagle_phys2020_fa07_lecture12

nagle_phys2020_fa07_lecture12 - Reminders Exam#1...

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1 15 Reminders…. • Exam #1 tomorrow (Tuesday September 24 at 7:30 pm in G1B30). • Please check out your seat assignment online. • There is a CAPA homework due on Friday (shorter). • Reading for last week Sections 17.7 – 17.11 • Reading ahead for this week All of Chapter 18. 16 Clicker Question A parallel plate capacitor is charge up (+Q on one plate and –Q on the other). The plates are isolated so the charge Q cannot change. The plates are then pulled apart so that the plate separation d increases. The total electrostatic energy stored in the capacitor? A) Increases B) Decreases C) Remains constant ----------------------------------------- -Q d QV CV C Q U 2 1 2 1 2 1 2 2 = = = 17 Where is this energy U? Answer = the electric field has energy. Energy density of E-field = . Vol U volume energy = () d A d E d A Vol CV = = 2 0 2 | | 2 1 . 2 1 v ε 2 0 | | 2 E v = Turns out work to charge capacitor is equal to energy stored. 18 What is this device? 19 Supernova instabilities National Ignition Facility at Livermore Lab 20

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2 21 22 What will happen when I put the screwdriver across the capacitor?
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nagle_phys2020_fa07_lecture12 - Reminders Exam#1...

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