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# A bar magnet is positioned near a coil of wire, as shown in Figure P20.15. What is the direction of the current in the resistor when the magnet is moved (a) to the left and (b) to the right?

## a. rightb. left

### Discussion

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##### Christina K.

Rutgers, The State University of New Jersey

##### Marshall S.

University of Washington

##### Aspen F.

University of Sheffield

### Video Transcript

Okay. Uh, so you have, Ah, bar magnet here is the North Pole is the South Pole. Uh, and you have a whole coiled machinery going on here. All right, So, um, we know that Ah, maybe a few lines point from go from north to south like that. So when the magnetic field, when the when the magnet is moved to the left. What's happened? What's happening is that magnetic field lines, since they go from north to south were initially pointing along the right of the coil on. And so since the magnet is moved, magnetic field strength decreases. It's moved away from the coil. What's happening is that the coil wants to it. Oh, opposed this change. And so it will induce more magnetic field to the to the right. Um and so you have an induced. And so you have no increase in the You have an induced current to the right because of this. Okay, uh, so, uh, that's what happens when it moves away. And then when it moves towards the magnetic field, but your toe worth the corn, what you have is that, um, the, uh, magnetic field to the right of the wire is increasing. So to oppose this change Ah, there will be a current induced in the opposite direction. So, um, in part A, you have a current from left to right and part B. We have a current, um, from right, two left, and that's it.

New Mexico State University
##### Christina K.

Rutgers, The State University of New Jersey

##### Marshall S.

University of Washington

##### Aspen F.

University of Sheffield