When we increase the current flowing through the coil (use a battery of two or more cells in place of one cell), the magnetic effect becomes stronger. When the number of turns in the coil is increased (the length of the conducting wire increases), the magnetic effect becomes stronger. When a conducting wire is coiled around a rolled sheet of paper and current is passed through the coil, it creates a magnetic field that becomes stronger when we insert an iron nail inside the sheet of paper roll.