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Test3-Turner - Arb Kellen Homework 15 Due Oct 6 2004 4:00...

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Arb, Kellen – Homework 15 – Due: Oct 6 2004, 4:00 am – Inst: Turner 1 This print-out should have 13 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 2) 10 points A positively charged particle enters a mag- netic field, as shown in the figure below. What is the initial direction of deflection? + + + + + + + + + + B in k j i ^ ^ ^ 1. ˆ F = - ˆ 2. ˆ F = + ˆ k 3. ˆ F = +ˆ correct 4. k ~ F k = 0, no deflection 5. ˆ F = - ˆ k 6. ˆ F = +ˆ ı 7. ˆ F = - ˆ ı Explanation: Basic Concepts: Magnetic Force on a Charged Particle: ~ F = q~v × ~ B Right-hand rule for cross-products. The force is given by ~ F = q~v × ~ B . ~ B = B - ˆ k · ~v = v (+ˆ ı ) q > 0 Therefore ~ F = q~v × ~ B = q v B h (+ˆ ı ) × - ˆ k ·i = q v B (+ˆ ) . 002 (part 2 of 2) 10 points A positively charged particle enters a mag- netic field, as shown in the figure below. What is the initial direction of deflection? B 45˚ k j i + θ ^ ^ ^ 1. ˆ F = +ˆ 2. ˆ F = - ˆ ı 3. ˆ F = - ˆ 4. k ~ F k = 0, no deflection 5. ˆ F = + ˆ k 6. ˆ F = - ˆ k correct 7. ˆ F = +ˆ ı Explanation: ~ B = B 2 [(+ˆ ı ) + (+ˆ )] ~v = v (+ˆ ) q > 0 Therefore ~ F = q~v × ~ B = q v B 2 (+ˆ ) × [(+ˆ ı ) + (+ˆ )] = q v B 2 - ˆ k · . 003 (part 1 of 1) 0 points Given: A long straight wire and a wire loop in the same plane. The long wire has a current flowing in the direction shown. The wire loop is moving in the direction shown.
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Arb, Kellen – Homework 15 – Due: Oct 6 2004, 4:00 am – Inst: Turner 2 I v wire loop wire straight The current in the loop is flowing 1. There is no current in the loop. 2. clockwise. correct 3. counter-clockwise. Explanation: Using the right hand rule, in the fol- lowing figure, and taking into considera- tion the direction of the magnetic field, we find that the direction of the current flow- ing in the loop is as shown in the figure. × × × × × × × × × I v i B 004 (part 1 of 4) 0 points Consider two long parallel wires which are perpendicular to the plane of the paper ( i.e. , the x - y plane. See figure). Both wires carry the same current, I . Wire #1 intersects the plane a distance a above point O and wire #2 intersects the plane a distance a below point O . Point C is equidistant from both wires and is a distance a from point O . a a a a O C D wire #2 wire #1 45 45 x y I II III IV O The direction of the magnetic field at C is 1. out of the plane. 2. in quadrant I. 3. in quadrant IV. 4. in the positive y direction. 5. in the positive x direction. correct 6. in quadrant III. 7. in the negative y direction. 8. in quadrant II. 9. into the plane. 10. in the negative x direction. Explanation: B 2 B 1 O C wire #2 wire #1 From the figure above, we can see by sym- metry that the y components of the magnetic fields cancel, leaving only the component in
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Arb, Kellen – Homework 15 – Due: Oct 6 2004, 4:00 am – Inst: Turner 3 the positive x direction.
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