I got two different answers last time so I l ask again.| Suppose a very long str

Question

I got two different answers last time so I l ask again.|

Suppose a very long straight wire were held perpendicular to the plane of the page such that it intersects the page at point D. Additionally, suppose the wire was being moved toward the top of the page. Would the current through the wire flow into the page, out of the page, or not at all? Into the Page Out of the page No current would flow Suppose instead that the wire were moved toward the left side of the page. Would the current through the wire flow into the page, out of the page, or not at all? Into the Page Out of the page No current would flow

Explanation / Answer

In (a) Consider the area to be the rectangle formed by the initial position of wire and final position. Or, it is basically the area swept by the wire moving towards the top of plane. The area vector of this area element is towards left. But magnetic filed is directed towards the top of the plane. Thus, magnetic flux or (phi=ec{A}.ec{B}=0)

Thus, the change in flux is also zero. Thus no current through the wire.

In case (b), the area element is towards top of the plane thus flux and change in flux as wire moves will be non zero.

the current in the wire flows in such a direction such that the force which results on the wire due to the current and the magnetic field opposes the motion of wire.

Now, force on the wire is given by (F=Lec{I} imesec{B})

we have that force should be towards right as the wire is moving towards left. magnetic field is towards the top of plane. Thus, current should be into the page according to right hand rule.

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