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Unformatted text preview: This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 4) 10.0 points Consider the situation in the figures below, in which there is a uniform electric field in the x direction and a uniform magnetic field in the y direction. In the first diagram, the proton is at rest. x y z B E (at rest) Proton For each example of a proton at rest or moving in the x , y , or z direction, which vector correctly gives the direction of the net magnetic force on the proton at this instant? (The zero vector indicates that there is no magnetic force on the proton.) 1. F B = , ,- F B 2. F B = , , F B 3. F B = , F B , 4. F B = ,- F B , 5. F B = F B , , 6. F B =- F B , , 7. F B = , , correct Explanation: Since the expression for the magnetic force is dependent upon velocity, F = q v × B, the magnetic force is zero because the proton is not moving. 002 (part 2 of 4) 10.0 points Here the proton is moving in the + x direction. x y z B E Proton v 1. F B = , , F B correct 2. F B = , ,- F B 3. F B = ,- F B , 4. F B =- F B , , 5. F B = , F B , 6. F B = F B , , 7. F B = , , Explanation: Recalling the magnetic force expression again, and using the right-hand rule, the mag- netic force points in the + z direction. 003 (part 3 of 4) 10.0 points Here the proton is moving in the + y direction. x y z B E Proton v 1. F B = , , correct 2. F B = , ,- F B 3. F B = , F B , 4. F B = F B , , 5. F B =- F B , , 6. F B = , , F B 7. F B = ,- F B , Explanation: Here the velocity is aligned with the mag- netic field, so the cross product is zero and the magnetic force is also zero. 004 (part 4 of 4) 10.0 points Be careful here. The proton is moving in the + z direction. x y z B E Proton v (+ z ) 1. F B = , , F B 2. F B = , ,- F B 3. F B = F B , , 4. F B =- F B , , correct 5. F B = , F B , 6. F B = ,- F B , 7. F B = , , Explanation: By the right-hand rule, the magnetic force is in in the- x direction. 005 (part 1 of 3) 10.0 points At a particular instant, a proton is traveling in the- x direction, with speed 6 × 10 5 m / s. At the location of the proton there is a magnetic field of magnitude 0 . 18 T in the- y direction, due to current running in a nearby coil. What is the magnetic force on the proton? Start by finding the x component, F B,x . (The charge on the proton is 1 . 6 × 10- 19 C.) Correct answer: 0 N....
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This note was uploaded on 10/25/2011 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas.
- Spring '08