What can increase the strength of the magnetic field from an electromagnet?

The strength of the magnetic field generated by an electromagnet can be enhanced by both increasing the applied voltage and increasing the number of loops of wire in the coil. When the applied voltage is increased, more current flows through the wire, which in turn generates a stronger magnetic field according to Ampère's Law. Additionally, increasing the number of loops or turns in the coil adds to the total amount of wire through which the current flows, effectively increasing the magnetic field strength. Each loop contributes to the overall magnetic flux, resulting in a cumulative effect, leading to an even stronger magnetic field.

Thus, option D perfectly captures both methods to enhance the magnetic field, making it the correct choice. This understanding is crucial in various applications of electromagnets, such as in medical equipment, where precise control of the magnetic field can impact functionality and safety.