I have created a simple electromagnet that is just an iron railroad spike with some thick insulated wire wrapped around it. This is connected to a dodgy, old motorbike battery (I'm thinking of being a decent battery...). I have looked up how you measure the strength, but I'm not sure what is the one I'm looking for. Is it magnetic flux density? If so, I found the formula for teslas: T = N/Am. How can I apply this to my magnet? I can find the Amperes with a multimeter, but I don't know how to find the Newtons... Also, with the metres part, is that the length of iron wrapped in the coil, or just the length of iron all together?