# Interesting thought about simple induction

• Jdo300
In summary, the conversation discusses the basic concepts of magnetic induction, particularly in the case of a stationary solenoid coil with a moving magnet. It is mentioned that when the magnet approaches the coil, a voltage potential is induced, resulting in a current in the windings. The opposite effect occurs as the magnet passes over the coil. The question is raised about what would happen if the coil was open-circuited while the magnet was approaching, but then shorted right as the magnet passed over the coil. It is then discussed that in this case, the energy would be stored capacitively in the windings and the behavior of the coil would be influenced by both inductance and capacitance. The capacitance can be estimated from tables
Jdo300
Hello All,

Was thinking about some of the basic concepts of magnetic induction, in the case of a stationary solenoid coil with a moving magnet crossing the face of the coil. We know that when the magnet approaches the face of the coil and the field increases, that a votlage potential (emf) is induced in the windings, which generates a current, i, in the windings. Also, as the magnet proceeds past the face of the coil, the magnetic field decreases and the opposite voltage potential is induced in the coil and a current is driven in the opposite direction.

Now assuming that I'm on par so far, I have made the assumption in the above example that the coil was either shorted to itself or across a load of some sort so that a current can actually flow when the emf from the magnet is induced into the windings. But what would happen if the coil was open-circuited while the magnet was approaching the coil, but then shorted to itself right as the magnet passed over the face of the coil? Would a current still be generated at that point in time (assuming that the magnetic field has not yet started decreasing). If a current is generated at this point, was the energy stored capacitively in the windings while the magnet was approaching and the coil was open-circuited? Or would nothing at all happen?

Thanks,
Jason O

EDIT: Argh.. Typos!

Last edited:
If the magnet is moving, and the coil is shorted, of course current has to flow. When the coil was open circuited, then the energy was indeed stored capacitively per W = 0.5 * C * V^2. Have I answered your question?

Claude

cabraham said:
If the magnet is moving, and the coil is shorted, of course current has to flow. When the coil was open circuited, then the energy was indeed stored capacitively per W = 0.5 * C * V^2. Have I answered your question?

Claude

Partially. I still have two more questions here. If the energy is stored capacitively in the windings of the coil, then how would one quantify this capacitance? Is it just the parallel parasitic capacitance between the windings? Also, once the winding is shorted with this potential in it, would the current discharge from the coil like a capacitor or would one expect to see the standard inductance behavior in this case? The reason I ask is because in this case, the potential is generated in the coil rather than applied to it from an external source, so I'm curious to know if the capacitive energy would still make the coil behave like a coil or like a capacitor?

Thanks,
Jason O

Jdo300 said:
Partially. I still have two more questions here. If the energy is stored capacitively in the windings of the coil, then how would one quantify this capacitance? Is it just the parallel parasitic capacitance between the windings? Also, once the winding is shorted with this potential in it, would the current discharge from the coil like a capacitor or would one expect to see the standard inductance behavior in this case? The reason I ask is because in this case, the potential is generated in the coil rather than applied to it from an external source, so I'm curious to know if the capacitive energy would still make the coil behave like a coil or like a capacitor?

Thanks,
Jason O

It behaves like a coil with some series resistance and shunt capacitance. At very low frequencies, the capacitance is negligible. The influence of the capacitance becomes more pronounced as freq increases. As far as quantifying the capacitance, it is non-linear and can be estimated from tables published by inductive component suppliers. An online search should turn up something. Is this helpful?

Claude

cabraham said:
It behaves like a coil with some series resistance and shunt capacitance. At very low frequencies, the capacitance is negligible. The influence of the capacitance becomes more pronounced as freq increases. As far as quantifying the capacitance, it is non-linear and can be estimated from tables published by inductive component suppliers. An online search should turn up something. Is this helpful?

Claude

Yes it is, thank you

## 1. What is simple induction?

Simple induction is a method of reasoning in which a general statement or principle is believed to hold true for all instances based on a limited number of observed cases. It is a fundamental tool in the scientific method and is used to form hypotheses and theories.

## 2. How does simple induction differ from deduction?

Simple induction and deduction are two different methods of reasoning. Deduction starts with a general principle or theory and applies it to specific cases, while simple induction starts with specific observations and generalizes to a broader principle or theory.

## 3. Can simple induction be used to prove a theory?

No, simple induction is not a method of proof. It can only provide evidence or support for a theory, but it cannot definitively prove it to be true.

## 4. What are the limitations of simple induction?

Simple induction is based on the assumption that the future will behave like the past, which may not always be true. It also relies on the accuracy and representativeness of the observed cases, which may be limited or biased.

## 5. How is simple induction used in scientific research?

Simple induction is commonly used in scientific research to form hypotheses and theories based on observed data. It is also used to make predictions and guide further experiments and investigations.

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