2
$\begingroup$

I performed an experiment where I connected a magnet to the end of a spring with the north side on the bottom. The magnet at the tip of the coil was aligned to pass through a column of coils of about 900 copper coils. The column of coils has the top coil connected to an extension wire which is connected to a variable resistor. The bottom coil is connected to an extension wire which is connected to the other port of the variable resistor, creating a series circuit. enter image description here Now, what I found intersting is that when I increase the resistance of within the circuit, the damping of the oscillations became greater. Now, this is contrary to what is most logical, since an increase in resistance causes a decrease in the current induced within the coils as a result of the change in the magnetic field relative to the coils (Lenz's law). These I think are known as eddy currents. But the questions still remains, how can an increase in resistance within the coils possibly cause more damping if it is decreasing the current opposing its motion as it enters the coil column.

enter image description here enter image description here enter image description here enter image description here enter image description here enter image description here enter image description here

$\endgroup$
  • $\begingroup$ In extreme case of infinite resistance, there will be no induced current, thus no damping. It is contrary to the logic. Do you have the experiment data, damping as a function of resistance? $\endgroup$ – wwwjjj Aug 25 '18 at 11:12
  • $\begingroup$ @wwwjjj I didn't calculate the values for damping as such, but I do have the experimental data for the change in force and induced emf over time. I will work on calculating the damping coefficients. How do I upload screenshots in the comments section of the page though? $\endgroup$ – Oussama Safi Aug 25 '18 at 11:22
  • $\begingroup$ You can edit the question, then add graphs. It would be nice if you can show the position/force/emf-time curves (same intial condition), for a wide range of different resistances. $\endgroup$ – wwwjjj Aug 25 '18 at 11:26
  • $\begingroup$ I apologise if it took me too long to repsond with the graphs $\endgroup$ – Oussama Safi Aug 30 '18 at 10:47
0
$\begingroup$

Damping implies losses.

If the coil is an open circuit, the current is zero. No losses.

If the coil is shorted, the current could be high, but the resistance could be very low, so the losses could be low as well - close to zero, if a coil was a superconductor.

From the above, it follows that, for a given setup, there must be some coil load resistance, which will cause maximum losses and, therefore, maximum damping.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.