Why can not we generate electricity with magnets?

[sach963]

If we can create a magnetic field with a solenoid, why can not we generate electricity with magnets?

 

[Bandersnatch]

Hi sach963, welcome to PF!

Why do you think it can't be done? Have you seen a bicycle dynamo?

 

[DEvens]

We do. The usual way to generate electricity is to move a magnet past a wire in some fashion.

http://en.wikipedia.org/wiki/Electric_generator

But it requires work to do so.

http://en.wikipedia.org/wiki/Lenz's_law
http://en.wikipedia.org/wiki/Conservation_of_energy

To get energy in the form of electrical power requires something to do the work of driving the generator. So there is no free lunch.

 

[Arjun J]

We can It is called electromagnetic induction. Just as we cannot create magnetic fields using point stationary charges, we cannot create electricity with a magnet at rest (We can but it requires that we move a conductor in a specific way near it). For more information try googleing "electromagnetic induction"

 

[sach963]

thank you all for the information.But just one more thing, wiil this cause the weakening of the magnet?

 

[Bandersnatch]

thank you all for the information.But just one more thing, wiil this cause the weakening of the magnet?

No, it won't. You're not extracting energy 'stored' in the magnet, you're extracting energy from the work you're doing using the magnet (like moving it back and forth next to a solenoid).

 

[sach963]

Thanks!

 

[CWatters]

Build your own "shake" powered flashlight..

 

[bland]

We can It is called electromagnetic induction. Just as we cannot create magnetic fields using point stationary charges, we cannot create electricity with a magnet at rest (We can but it requires that we move a conductor in a specific way near it). For more information try googleing "electromagnetic induction"

Relativity is says that you cannot say whether it is the coil or the magnet which is at rest with respect to the other. It's simply a matter of what is more convenient to build.

 

[mfb]

I added a graph. Red is the fraction of electricity power produced via moving magnets (or moving wires in magnetic fields, which is the same), dark blue all other production methods combined (which is just photovoltaics, for ~1%).

 

[aabottom]

And a moving magnet phonograph cartridge generates an electric signal by a magnet that is moved back & forth, up & down by the grooves in a phonograph (Long Play- LP, 45s, vinyl).

 

[Npdot]

And a moving magnet phonograph cartridge generates an electric signal by a magnet that is moved back & forth, up & down by the grooves in a phonograph (Long Play- LP, 45s, vinyl).

Also, there are moving coil phonograph cartridges which generate an electric signal via a coil moved back & forth, etc. by the grooves of a vinyl phonograph record. The coil is moving realtive to the magnetic field of a small magnet solidly afixed to the phonograph cartridge. In this case we visualize the coil as moving and the magnetic field as stationary.

Generally speaking, the physical principle (magnetic induction) and the associated math gives us the same result (the same electric current in the wire) regardless of whether we visualize the wire as moving relative to a stationary magnet field, or the magnetic field moving relative to a stationary wire.

 

[DEvens]

And a moving magnet phonograph cartridge generates an electric signal by a magnet that is moved back & forth, up & down by the grooves in a phonograph (Long Play- LP, 45s, vinyl).

Some phonographs work this way. Some use a piezoelectric crystal. There might be other mechanisms. Some materials change their resistance under changes of stress, for example. I'm not sure if any phonographs use that method.

I do miss my vinyl collection. Why did I ever get rid of it?