# Electric generators

1. Apr 1, 2010

### nbsmith

I know that the iron core of a solenoid will result in a higher magnetic field than a hollow core when a current is running through it.

I'm wondering if the reverse is true. Will an iron core result in a larger current when the solenoid is exposed to a changing magnetic field?

I want to create a simple generator where one or two electric coils are rotating between some magnets and I am wondering if having an iron core will create a larger current.

Any explanation as to why would be appreciated too.

Thanks.

2. Apr 3, 2010

### cyclopath

Let's see here. We have the following from Ampere's law:
B = mu NI/h
Solving this for the current, we get:
I = Bh/(N mu)
Where mu depends on the core material. Using iron (or most other metals) this value will be greater than mu_nought = 1/(4pi x10^-7) ~ 1.2566650×10^-6.
The movement of the core inside the solenoid causes a changing magnetic field ($$\hat{B}$$) which causes an induced current (I). As such, the current depends on the changing magnetic field, as well as the permeability of the space inside (our mu.) As mu_iron > mu_hollow, where mu_hollow=mu_nought, we will get a smaller induced current using an iron core from the same changing magnetic field, $$\hat{B}$$. This would mean changing the position of the core inside of the solenoid by the same amount and at the same rate.

So, if the changing magnetic field is the same in both trials (one with a hollow solenoid, one with an iron core) we get a larger induced current using a hollow core as a result of the smaller permeability value. As such, we will get a smaller induced current when using an iron core as a result of its larger permeability value.

3. Apr 6, 2010

### Syrtd

Since there is the above exposition, I'll just add in simpler language also that the added resistance of the iron core, if the solenoid is formed of uninsulated wire so there is contact, will add to the resistance of the system and therefore reduce current flow per "V=P/I."

This rarely has any purpose to be considered since most solenoids are insulated... but... life happens.