Can I covert magnetic energy to electrical energy?

[Ferdous Hossain]

Hello

Before I start, I would like to clarify that I know Perpetual Motion is not possible & Energy can neither be created nor destroyed, But Can be change from one form to another.

That's exactly my point. If I could convert energy from one to another, then why couldn't I just harness energy from a magnet. A Neodymium magnet(N52) can last roughly for 300 years. Why is it so impossible to get any power from a magnet.

Thank you all...

 

[lekh2003]

Hello

Before I start, I would like to clarify that I know Perpetual Motion is not possible & Energy can neither be created nor destroyed, But Can be change from one form to another.

That's exactly my point. If I could convert energy from one to another, then why couldn't I just harness energy from a magnet. A Neodymium magnet(N52) can last roughly for 300 years. Why is it so impossible to get any power from a magnet.

Thank you all...

Because electrical energy can only be created by a change in magnetic field. The magnet has to be moving in some manner to produce electricity. One method to do this is a water wheel and attaching a magnet to it. This is the concept of hydroelectric energy.

 

[Ferdous Hossain]

Because electrical energy can only be created by a change in magnetic field. The magnet has to be moving in some manner to produce electricity. One method to do this is a water wheel and attaching a magnet to it. This is the concept of hydroelectric energy.

ok. But why the magnetic field have to be a rotating one?
why a still magnetic field can't do it?

 

[lekh2003]

ok. But why the magnetic field have to be a rotating one?
why a still magnetic field can't do it?

I'm not sure. The empirical results showed that magnetic flux generated a current, but not a plain magnetic field.

 

[Dale]

But Can be change from one form to another.

That's exactly my point. If I could convert energy from one to another, then why couldn't I just harness energy from a magnet.

Energy can be converted from one form to another, and it can be converted from magnetic to electrical. However, there is not very much energy in a typical magnet and in order to extract it you must reduce the magnetic field. If the magnetic field is not reduced then no energy has been extracted from it.

The explanation why is fairly straightforward, but it involves vector calculus. So I don’t think that I can do it at a B level, it is I material.

 

[Ferdous Hossain]

Energy can be converted from one form to another, and it can be converted from magnetic to electrical. However, there is not very much energy in a typical magnet and in order to extract it you must reduce the magnetic field. If the magnetic field is not reduced then no energy has been extracted from it.

The explanation why is fairly straightforward, but it involves vector calculus. So I don’t think that I can do it at a B level, it is I material.

My brother have graduated this year. so, he can explain it to me. Please explain it & what did you mean by reducing magnetic field. If there is not much energy in a magnet then, how can it pull things toward it for 300 years?

 

[Dale]

My brother have graduated this year. so, he can explain it to me. Please explain it & what did you mean by reducing magnetic field.

OK, your brother needs to explain Poynting's theorem to you:
$$\frac{1}{2}\frac{\partial}{\partial t}\left(\epsilon_0 \mathbf{E}\cdot\mathbf{E} + \frac{1}{\mu_0}\mathbf{B}\cdot\mathbf{B}\right)+\frac{1}{\mu_0}\nabla \cdot (\mathbf{E}\times\mathbf{B}) + \mathbf{J}\cdot\mathbf{E}=0$$
The magnetic energy is the $\mathbf{B}\cdot\mathbf{B}$ term. The only way to convert energy from the magnetic field to one of the other forms is to reduce it.

If there is not much energy in a magnet then, how can it pull things toward it for 300 years?

Remember that work is not just a force, it is a force times a distance ($W=\mathbf{f}\cdot\mathbf{d}$). So it is not enough just to exert a force for 300 years, it must exert a force on something in the direction that it moves for 300 years. That doesn't happen.

A magnet can exert a force on a piece of iron, and while the iron is away from the magnet it can move towards it and work can be done. As it moves towards the magnet, the magnetic field is reduced (per Poynting's theorem), but once the iron reaches the magnet it stops moving, the work stops, and the reduction of the field stops. In order to do work on the iron again, it must first be pulled away from the magnet via some external force, work is done on the field by the external force, and the field is increased. The 300 year supply of force is not a 300 year supply of energy, the energy needs to be replenished via the external force every time work is done.

 

[russ_watters]

That's exactly my point. If I could convert energy from one to another, then why couldn't I just harness energy from a magnet. A Neodymium magnet(N52) can last roughly for 300 years. Why is it so impossible to get any power from a magnet.

Because it only lasts 300 years if you aren't using its energy up!

 

[Ferdous Hossain]

OK, your brother needs to explain Poynting's theorem to you:
$$\frac{1}{2}\frac{\partial}{\partial t}\left(\epsilon_0 \mathbf{E}\cdot\mathbf{E} + \frac{1}{\mu_0}\mathbf{B}\cdot\mathbf{B}\right)+\frac{1}{\mu_0}\nabla \cdot (\mathbf{E}\times\mathbf{B}) + \mathbf{J}\cdot\mathbf{E}=0$$
The magnetic energy is the $\mathbf{B}\cdot\mathbf{B}$ term. The only way to convert energy from the magnetic field to one of the other forms is to reduce it.

Remember that work is not just a force, it is a force times a distance ($W=\mathbf{f}\cdot\mathbf{d}$). So it is not enough just to exert a force for 300 years, it must exert a force on something in the direction that it moves for 300 years. That doesn't happen.

A magnet can exert a force on a piece of iron, and while the iron is away from the magnet it can move towards it and work can be done. As it moves towards the magnet, the magnetic field is reduced (per Poynting's theorem), but once the iron reaches the magnet it stops moving, the work stops, and the reduction of the field stops. In order to do work on the iron again, it must first be pulled away from the magnet via some external force, work is done on the field by the external force, and the field is increased. The 300 year supply of force is not a 300 year supply of energy, the energy needs to be replenished via the external force every time work is done.

Thank you very much...
Though it was one of my childhood dream to make something like that, now it completely makes sense...

 

[Ferdous Hossain]

Because it only lasts 300 years if you aren't using its energy up!

Thank you very much...