How to use transformers to create an electromagnet?

[Stephenk53]

I want to make a powerful electromagnet using a transformer, to start I wish to to make a weak magnet using it then work up from there to ensure I make little to not mistakes since I am inexperienced with engineering. I was planning on using a transformer I got from a power supply. I have taken the power supply fully apart but if you think it would be easiest to start with a dismantled power supply, I have some of those as well.

So what could I use to power it?

What are possible problems I could face to make it and how?

 

[.Scott]

It is actually pretty easy to turn a power transformer into an electromagnet.
Here is a link: http://www.instructables.com/id/Microwave-Electromagnet/
Note that the source of the transformer does not have to be a microwave oven as described in that article.