What factors of an electromagnet affect the strength of the magnetic field?
One of them is how many coils go around the electromagnet.
also the amout of current flow< and the type of core material.
An electromagnet will maintain a charge as long as current continues to flow through it. Strengthening the charge is a matter of changing, or adjusting the components that enable the charge to flow. There are many ingredients that affect electromagnet strength. The length and width of the magnetic field, the amount of resistance the current encounters, the pulling power of the magnet itself, all determine how strong your electromagnet will be.