high schoool science project

[jtheobald@xxxxxxxxxxxxxxxx]

Hello,
This is the first site that offered any information that I might 
have the chance of understanding. I am very intrested in magnets but 
don't know where to start. My physices teacher in high school showed 
me a device that most similarly remindes me of a selinoid valve. the 
device was built with a coil attached to a base with an extension 
cord sodesrd to the 2 ends of the coil. A cylindrical ferrous core 
was placed in the center. When pluged into an electrical source it 
was able to suspend a metalic ring in the air. it also could launch 
the ring into the air if placed around the core and then plugged in.

My questions are:
1. How can i calculate the upward force of the magnetic feild?

2. How can i calculate the power required to lift the metalic
ring a specific distance.
3. Lastly, if the total power in watts renmains constant for any 
electromagnet, will a power source with a higher voltage and 
very low amperage, or lower voltage and higher amperage 
produce a greater magnetic feild?