Answer:
The strength of the electromagnet depends on the Voltage - electric current flowing through the conducting loop or wires.
By adding batteries an electromagnet can be made stronger but it depends on the relative resistances of the two components. In simple words, its how many currents can the components conduct. This can be done by connecting the batteries in series to increase the voltage across the electromagnet to increase the current. In this case, the strength of the electromagnet is directly proportional to the total sum of the batteries' voltage.
