Lenz's Law and Gravity
A mass
pulls the conducting bar through a vertically oriented magnetic field.
In the above picture, a mass falls under the influence of gravity, pulling with it a conducting bar of mass , resistance , and length that sits on a U-shaped piece of metal in a vertically oriented magnetic field perpendicular to the plane of the U, pointing in the positive-z direction. In which direction does the induced current flow?
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1 solution
As the mass M pulls the bar with it, the area of the closed conducting loop through which the magnetic field penetrates increases over time, so the magnetic flux increases in the positive-z direction over time. By Lenz's law, a magnetic field must be induced in the negative-z direction to oppose this. A clockwise current accomplishes this.