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9. [1pt] The diagram depicts a wire of length L that is suspended from two wire

ID: 1445197 • Letter: 9

Question

9. [1pt] The diagram depicts a wire of length L that is suspended from two wire springs of spring constant k. The system is connected to a direct current source. A magnetic field B, out of the page and perpendicular to the wire, is turned on. Then the current I is turned on; the wire will move to a new equilibrium position. The wire is free to move in 3 dimensions. For each of the following statements answer True, False, or Cannot tell. E.g., if the first statement is true, the second is false, and there is not enough information to answer the rest, enter TFCCC. If the current direction were reversed from that shown on the diagram, the wire would move up to a new equilibrium position. If the direction of the magnetic field were into the page, the wire would move up to a new equilibrium position. If the direction of the magnetic field were parallel to the current in the wire of length L, the wire would move out of the page to a new equilibrium position. If the direction of the magnetic field were down (in the plane of the page), the wire would not move to a new equilibrium position. For the situation depicted in the diagram, the wire will move down to a new equilibrium position.

10. [1pt]
Assume the situation shown in the diagram, with L = 0.420 m, I = 0.200 A, B = 2.75 T (out of the page), and k = 0.585 N/m for each spring.
How far will the wire move to reach its new equilibrium position if the current is turned on?

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Explanation / Answer

The direction of the current is perpendicular to the direction of the magnetic field, and the resulting magnetic force is directed vertically downwards. The wire will thus move down until the magnetic force is balanced by the spring forces. In the equilibrium position the springs will be stretched.