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Unformatted text preview: Daniels, Matthew – Final 1 – Due: Dec 16 2006, 6:00 pm – Inst: Ditmire 1 This print-out should have 46 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points A static uniform magnetic field is directed into the page. A charged particle moves in the plane of the page following a counter- clockwise spiral of decreasing radius as shown. B B Neglect the effect due to gravity. What is a reasonable explanation? 1. The charge is neutral and speeding up. 2. The charge is positive and with a constant speed. 3. None of these 4. The charge is neutral and with a constant speed. 5. The charge is negative and with a con- stant speed. 6. The charge is positive and slowing down. correct 7. The charge is negative and slowing down. 8. The charge is neutral and slowing down. 9. The charge is positive and speeding up. 10. The charge is negative and speeding up. Explanation: We know that when a charged particle moves in a uniform magnetic field with a constant speed, it undergoes a circular mo- tion with the centripetal force provided by the magnetic force, namely m v 2 r = q v B , so we know that the radius is in fact propor- tional to the speed, r = m q B v . Since the particle follows a spiral of decreasing radius, we can judge that it is slowing down. The magnetic force ~ F = q~v × ~ B must be in the direction for the centripetal force- ˆ r (pointed inward) of this particle in counter- clockwise circular motion. Since ~v × ~ B is in the negative ˆ r direction, the particle has a positive charge. keywords: 002 (part 1 of 1) 10 points Which travels most slowly in glass? 1. Red light 2. Orange light 3. Yellow light 4. Violet light correct 5. Brown light 6. Green light 7. Blue light Explanation: n = c v Since violet light is refracted more than the light of other frequencies its index of re- fraction is the highest, making its speed the smallest. In other words, violet light travels slowest in glass. Daniels, Matthew – Final 1 – Due: Dec 16 2006, 6:00 pm – Inst: Ditmire 2 keywords: 003 (part 1 of 1) 10 points When a potential difference of 65 V is ap- plied to the plates of a parallel-plate capaci- tor, the plates carry a surface charge density of 38 nC / cm 2 . The permittivity of a vacuum is 8 . 85419 × 10- 12 C 2 / N · m 2 . What is the spacing between the plates? Correct answer: 1 . 51453 μ m. Explanation: Let : σ = 38 nC / cm 2 = 0 . 00038 C / m 2 , V = 65 V , and ² = 8 . 85419 × 10- 12 C 2 / N · m 2 . s = ² V σ = (8 . 85419 × 10- 12 C 2 / N · m 2 )(65 V) (0 . 00038 C / m 2 ) = 1 . 51453 × 10- 6 m = 1 . 51453 μ m . keywords: 004 (part 1 of 2) 10 points An inductor and a resistor are connected with a double pole switch to a battery as shown in the figure....
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This note was uploaded on 06/23/2008 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas.
- Spring '08