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Unformatted text preview: Version One – Homework 4 – Savrasov – 39821 – Apr 16, 2007 1 This print-out should have 8 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. Air Filled Capacitor S 26:02, trigonometry, numeric, > 1 min, fixed. 001 (part 1 of 1) 1 points An air-filled capacitor consists of two parallel plates, each with an area A , separated by a distance d . A potential difference V is applied to the two plates. The magnitude of the surface charge density on the inner surface of each plate is 1. σ = ² ( V d ) 2 2. σ = ² V d 3. σ = ² d V 4. σ = ² µ V d ¶ 2 5. σ = ² µ d V ¶ 2 6. σ = ² V d correct 7. σ = ² V d 8. σ = ² ( V d ) 2 Explanation: Use Gauss’s Law. We find that a pillbox of cross section S which sticks through the surface on one of the plates encloses charge σ S . The flux through the pillbox is only through the top, so the total flux is E S . Gauss’ Law gives σ = ² E = ² V d Alternatively, we could just recall this result for an infinite conducting plate (meaning we neglect edge effects) and apply it. keywords: Capacitance of a Sphere 26:02, trigonometry, numeric, > 1 min, nor- mal. 002 (part 1 of 2) 1 points An isolated conducting sphere can be consid- ered as one element of a capacitor (the other element being a concentric sphere of infinite radius)....
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