PHY 91880 Midterm 3 Exam 2020

Version 046/AACDC – midterm 03 – turner – (93000) 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 An infinitely long straight wire carrying a current I1 = 37 A is partially surrounded by a loop as in figure. The loop has a length L = 31.5 cm, a radius R = 11.1 cm, and carries a current I2 = 29.7 A. The axis of the loop coincides with the wire. R L I1 I2 Calculate the force exerted on the loop. 1. 311.146 2. 1247.4 3. 593.321 4. 566.24 5. 1691.62 6. 261.6 7. 509.09 8. 274.081 9. 1129.34 10. 3132.88 Correct answer: 1247.4 μN. Explanation: Let : I1 = 37 A, I2 = 29.7 A, L = 31.5 cm = 0.315 m, and R = 11.1 cm = 0.111 m. The central wire creates field ~B = μ0 I1 2  R counterclockwise . The curved portions of the loop feels zero force since ~l × ~B = 0 there. The straight portions both feel I2~l × ~B forces to the right, amounting to ~F = I2 2 L μ0 I1 2  R = μ0 I1 I2 L  R to the right k~F k = μ0 (37 A) (29.7 A) (0.315 m)  (0.111 m) = 0. N = 1247.4 μN .