Magnet falling thru copper tube -- How does the process occur visually?

[notsosmrt]

 

[tech99]

I think it is correct. The current induced in the tube circulates round it and turns it into a single turn solenoid. This produces a vertical magnetic field opposing that of the magnet.

 

[tech99]

I am, however, very interested that the magnet sounds as if it is spinning in the tube.

 

[kuruman]

The magnet is not spinning because there can be no torque acting on it. The sounds you hear is most likely clanking as it hits the sides of the tube. Now for the explanation. Look at the left drawing in the figure below. There are induced currents in the tube (Shown in cross section) that circulate in opposite directions in the segments of the tube above and below the instantaneous position of the middle of the falling magnet at the dotted line. Typical rings of induced current are shown. Above the magnet the flux lines are decreasing as the magnet falls therefore the induced current will flow as shown to reinforce the decreasing "up lines". Below the magnet the flux lines are increasing in the up direction, therefore the induced current will flow as shown to decrease them.

Now look at the right drawing in the figure. The superposition of the magnetic fields produced by the sum total of all the rings above the magnet is equivalent to a "permanent" magnet oriented as shown. Likewise for the total sum of all the rings below. Note that the top equivalent magnet attracts the falling magnet while the bottom equivalent magnet repels it. In short, the induced current in both segments of the copper tube runs in the direction that always opposes the motion of the falling magnet. That's magnetic braking.

 

[tech99]

As the magnet descends, the circulating current rings move down the tube. So I presume there is a small downward component of current, maybe corresponding to the Ohmic losses.