Lenz's Law in action with different length magnets

In summary: F=mg) would be greater for the longer magnet. Additionally, the length of the magnet may also affect the amount of electrical current generated within the conductor, further contributing to the difference in rate of falling. This can be explained by Lenz's Law, which states that an induced current will flow in a direction to oppose the change in magnetic field that caused it. In summary, the difference in rate of falling between the 15cm and 3cm bar magnets can be attributed to the extra weight and length of the 15cm magnet, as well as the effects of Lenz's Law on the amount of electrical current generated within the conductor.
  • #1
magnetics
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Hi,
I was doing an experiment with Neodymium magnets and a long copper pipe (3cm internal diameter) to see Lenz's Law in action. At first I used a long bar magnet (about 15cm long) and there was little resistance to the magnet falling through the pipe. It was only slightly slower than a non-magnetic object. I then used a bar magnet of the same material and diameter that was only 3cm long and this magnet fell about 5 times slower. It took around 5sec to fall through the pipe compared to around one second for the 15cm magnet.

Can someone please describe why there is such a difference in the rate of falling (including using maths)?

It must have to do with the amount of electrical current each magnet generates within the conductor (copper pipe) and the extra weight of the longer magnet since F = mg.

Thank you.
 
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  • #2
magnetics said:
Can someone please describe why there is such a difference in the rate of falling (including using maths)?
<The fall of a strong magnet inside a conducting pipe is damped by the gradually increasing and opposing magnetic force that

the pipe wall exerts on the magnet. If the pipe is long enough, the magnet eventually reaches a constant terminal

speed. The braking force on the magnet arises from circular eddy currents, also known as Foucault currents. These eddy

currents are generated in the pipe by the e.m,f, induced in the pipe by the time-varying magnetic flux that the falling magnet

produces.>

For details see <http://www2.fisica.unlp.edu.ar/materias/FEIII/OLD/2012/AJP000193.pdf> [Broken]
 
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  • #3
I would say that the extra weight of the long magnet was the major factor for the difference
 

1. How does Lenz's Law explain the behavior of different length magnets?

Lenz's Law states that when a magnetic field is induced by a changing magnetic field, the direction of the induced field is always such that it opposes the change that produced it. This means that when a magnet is moved towards a conducting material, such as a copper wire, the resulting induced current will create a magnetic field that opposes the motion of the magnet. The length of the magnet affects the strength of the induced current and therefore the strength of the opposing magnetic field.

2. Why do longer magnets create a stronger opposing magnetic field?

The length of a magnet determines the number of magnetic field lines that are present. When a magnet is moved towards a conducting material, the changing magnetic field induces a current in the material. This current, in turn, creates a magnetic field that opposes the motion of the magnet. The longer the magnet, the more magnetic field lines are present and the stronger the induced current and opposing magnetic field will be.

3. How does the strength of the magnetic field affect the behavior of different length magnets?

The strength of the magnetic field directly affects the strength of the induced current and the opposing magnetic field. A stronger magnetic field will induce a stronger current, leading to a stronger opposing magnetic field. This means that a longer magnet with a stronger magnetic field will create a larger opposing force than a shorter magnet with a weaker magnetic field.

4. Can Lenz's Law be applied to magnets of all shapes and sizes?

Yes, Lenz's Law can be applied to magnets of all shapes and sizes. The law is based on the principles of electromagnetism and applies to any situation where a changing magnetic field induces a current. This includes situations with magnets of varying lengths, shapes, and strengths.

5. How is Lenz's Law used in real-world applications?

Lenz's Law has many practical applications, including in generators and motors. In generators, the motion of a magnet near a copper wire induces a current that can be converted into electrical energy. In motors, the interaction between the magnetic fields of two magnets creates motion. Lenz's Law also explains the braking effect in eddy current brakes, where a magnet moving near a conducting material creates an opposing magnetic field that slows down the motion of the magnet.

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