Brass Pendulum and Lenz's Law

A potential difference is induced across the brass pendulum, and the current flows such that it opposes the motion of the pendulum (due to Lenz's Law).

Brass is not a magnetic material, so the magnet is not slowing down by attracting the brass (as shown by the fact that the pendulum with slits in is not slowed down). However, when the pendulum with slits in is swung through the magnetic field, the eddy currents (which cause the pendulum to slow) are not so free to move within it. Thus Lenz's Law does not have as much effect; the current does not flow as much, so the motion is not opposed as much.

This demonstrates Lenz's Law, and why a laminated core is more efficient in a transformer.

Category:

Science & Technology

Tags:

• lenz's law
• electromagnetic induction
• transformers

[Dogslax3333]

I thought this was stopped by an Eddy Current? maybe I'm wrong

[phydotsi]

@Dogslax3333

No, you're right. Please have a look through the video description - I mention eddy currents there. The effect of Lenz's Law is reduced by the slits in the brass, as the eddy currents are not as free to flow; when the eddy currents are limited, the pendulum swings for longer.

[elrddm]

@CrusstyJugglers Eddy currents generate internal friction which convert energy into heat. The brass pendulum should have a measurable increase in temperature.

[CrusstyJugglers]

I know conservation of energy laws won't be broken in this experiment, but can somebody explain why? Some kind of electrical energy being generated?

[vedantganeriwala]

hi! i tried a slightly different experiment.

i used a pendulum with an iron bob.

i measured the time period of the pendulum.

and then i used a bar magnet and allowed the pendulum to oscillate directly above the bar magnet. the oscillation was in the direction of north south of the bar magnet i.e. along the bar magnet. the mean position the same as the equatorial axis of the magnet. i found that the time period with the magnetic field decreases, pendulum oscillates faster. why does this happen?

[kfstevens2370]

cool demo! thanks