Final answer:
The magnetic field inside a current-carrying coil can be increased by enhancing the current through the coil, inserting an iron core, or increasing the number of loops in the wire coil; therefore, all the listed factors contribute to a stronger magnetic field.
Step-by-step explanation:
The magnetic field inside a current-carrying coil increases with several factors.
If the current is increased, the magnetic field strength also increases due to the higher flow of charge carriers which produce a stronger magnetic field. Similarly, when an iron core is inserted into a coil, it becomes magnetized and strengthens the overall magnetic field due to the coil.
This process is known as magnetic induction, where the material inside the coil amplifies the magnetic field due to the alignment of its magnetic domains. Furthermore, increasing the number of loops in the wire coil absolutely leads to a more substantial magnetic field, as each loop contributes to the field inside the coil, and more loops mean more additive contributions.
Therefore, the correct answer to which factors can increase the magnetic field inside a current-carrying coil is all of the above: current increase, the insertion of an iron core, and an increase in the number of wire loops.