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Unformatted text preview: Version 093 – Exam 4 – chiu – (57460) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A length of wire whose total resistance is R is made into a loop with two quarter-circle arcs of radius r 1 and r 2 and two straight ra- dial sections as shown in the figure above. A very long solenoid is positioned as shown, go- ing into and out of the page. The solenoid consists of N turns of wire wound tightly onto a cylinder of radius r and length d , and it carries a counterclockwise current I s that is increasing at a rate dI s dt . Choose the correct statements. The direction of the current is in the fan- shaped loop is Ia) clockwise Ib) counterclockwise The direction of the magnetic field at C due to the larger arc with radius r 2 is IIa) into the plane IIb) out of the plane The direction of the net magnetic field at C is IIIa) into the plane IIIb) out of the plane 1. Ib, IIa, IIIb 2. Ia, IIa, IIIb correct 3. Ia, IIb, IIIb 4. Ib, IIb, IIIb 5. Ib, IIb, IIIa 6. Ib, IIa, IIIa 7. Ia, IIb, IIIa 8. Ia, IIa, IIIa Explanation: Ia: Since the solenoid B field is out and increasing, Faraday’s law implies that B ind within the loop is into the plane. So the induced current is clockwise. IIa: The direction of the magnetic field at C due to the current segment of larger arc at C is into the plane. IIIb: The direction of the net magnetic field at C is along the direction of the dominating field. The dominating field is contributed by the small arc. The corresponding B field is out of the plane 002 10.0 points A pulse of electromagnetic radiation propa- gates with v = ( , , c ) . The electric field is E = ( 1 , 1 , ) N/C. Which is the correct magnetic field vector? 1. B = (− c, c, ) T 2. B = ( c, c, ) T 3. B = (− 1 , − 1 , ) T Version 093 – Exam 4 – chiu – (57460) 2 4. B = (− 1 /c, 1 /c, ) T correct 5. B = ( 1 /c, 1 /c, ) T 6. B = ( 1 , − 1 , ) T 7. B = (− c, − c, ) T 8. B = ( c, − c, ) T Explanation: The correct answer should satisfy both con- straints (1) ˆ E × ˆ B = ˆ k (2) E = c B The reader should verify for themselves that both equalities are satisfied by the solution. 003 (part 1 of 2) 5.0 points In the figure shown above, the magnetic field is uniform and out of the page inside a circle of radius R, and is essentially zero outside the circular region. The magnitude of the magnetic field is changing with time; as a function of time the magnitude of the magnetic field is ( B + bt 3 ), where B = 1 . 5 T, b = 1 . 4 T / s 3 , r 1 = 0 . 036 m, r 2 = 0 . 53 m, t = 1 . 3 s and R = 0 . 17 m. Please choose the correct pair of state- ments....
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This note was uploaded on 05/22/2011 for the course CHEM 302 taught by Professor Mccord during the Spring '10 term at University of Texas.
- Spring '10