In Figure (a), the North end of a permanent magnet is pushed into the loop from

Question

In Figure (a), the North end of a permanent magnet is pushed into the loop from left to right (indicated by the red velocity vector above the magnet). Since the magnetic field is stronger closer to the magnet, the magnetic flux is increasing. Since magnetic field lines point away from the North end of a magnet (indicated by the direction arrows on the blue magnetic field lines), the magnetic flux is produced by magnetic field lines that point to the right. Thus, we have determined item 1 above: the change in flux that is occurring within the loop in Figure (a): increasing flux caused by magnetic field lines pointing to the right. To evaluate item 2 above, you must understand the direction of magnetic field lines produced by a current loop. You can determine this with a variation of Right-Hand Rule #2. Curl your fingers in the sense of the current, and your thumb points in the direction of the magnetic field. Take a moment to verify the magnetic field lines produced by the current loop in Figure (b). Curl the fingers of your right hand in the sense of the current, and your thumb will be point to the left. Thus, the current induced in Figure (a) must flow so as to oppose the change described above. since the rightward flux is increasing, the induced current must keep the flux from increasing. Thus, the right -pointing magnetic field of the magnet is partly cancelled by the left-point magnetic field produced by the induced current. As viewed from the left, this current is counter-clockwise. Use the animation above to verify that in this situation, current flows as indicated in Figures (a) and (b). As another example, consider Figures (c) and (d) above. In this case, the North end of the magnet is being pulled away from right to left. In each case below, select the most appropriate answer. The change in flux is: flux caused by magnetic field lines pointing to the To oppose this change, the induced current must keep the flux from . Thus, the induced current produces a magnetic field that points to the . Thus, as viewed from the left, the induced current is . Suppose that the polarity is reversed in the Figure above so that the south end of the magnet is closer to the loop in each case. The South end is pushed into the loop from left to right. The change in flux is: flux caused by magnetic field lines pointing to the To oppose this change, the induced current must keep the flux from . Thus, the induced current produces a magnetic field that points to the . Thus, as viewed from the left, the induced current is . The south end is pulled away from the loop from right to left. The change in flux is: flux caused by magnetic field lines pointing to the . To oppose this change, the induced current must keep the flux from . Thus, the induced current produces a magnetic field that points to the . Thus, as viewed from the left, the induced current is .

Explanation / Answer

1.) Decreasing
2.) Right.
3.) Decreasing.
4.) Right.
5.) Clockwise.

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