Answer:
d. poles
Explanation:
Magnetic field created by a solenoid:
The magnetic field created by a solenoid is increased by increasing the intensity of the current, by increasing the number of turns and by introducing a piece of iron inside the coil (electromagnet).
Solenoid coil with air core constructed with bare copper wire spirally wound and protected with insulating varnish. If we supply this coil with electric current using any source of electromotive force, such as a battery, for example, the flow of the current that will circulate through the coil will lead to the appearance of a magnetic field of a certain intensity around it.
Solenoid coil to which a metal core such as iron (Fe) has been introduced. If we compare the previous coil with air core with the coil of this illustration, we will see that now the lines of magnetic force are much more intensified as they have become an electromagnet.
