Efficient and Accurate Power Sources for Electromagnets: What Are My Options?

[Alieneater]

Homework Statement

What can I purchase so that I have a constant voltage that is cheap for my electromagnet and you can adjust to how many volts I want? Batteries will run out of power and not give good results. Also is there another easy way to precisely meaure the strength of the electromagnet other than using paperclips?

Homework Equations

none

The Attempt at a Solution

I don't know.

 

[Alieneater]

What I want is a power source other than batteries that won't run out of energy because once the batteries lose power, my results will be wrong.

 

[Alieneater]

Why won't anyone help me!